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Thread: Flashlight Tint/Color Reference

  1. #1

    Lightbulb Flashlight Tint/Color Reference

    Flashlight Tint/Color Reference



    Introduction
    I’ve been working on a new technique, photographing the color (aka tint) of light, as projected from flashlights and other sources. These are photos, not of flashlights, beamshots or bounceshots, but of the color of the actual light being projected.

    I want to make choosing a flashlight tint as easy as choosing a color at the paint store. View the profile for a given bulb or emitter and instantly know its color. Then compare 2+ profiles and see (first hand) which is warmer or cooler and by how much. The details are quite abstract, but the results are not. Read on or jump to the Use section to get started. And see post 30 if you start to feel



    Theory
    Have a look at this graphic:



    This is the spectrum of natural color (see note 3), from red to blue, by which we see. Not the color of objects but the color of the light that illuminates objects. Look at a red chair outside at noon, then put the same chair inside, next to a 100 watt bulb. It will look that much more red. The closer to "white" a given light source, the easier it is to see the “true” colors in the space we are viewing.

    LEDs tend toward blue. The older/cheaper an LED is, the bluer it tends to be. The holy grail of LEDs is to be as white as possible. Incans tend toward yellow. The lower the voltage, the yellower they tend to be. The holy grail of incans is to be as white as possible. Looking at the complete spectrum above, there is but one point in the middle, one white that both technologies strive for - balanced white.

    Have a look at the CCT column on the Welch Allyn bulb site:
    http://www.walamp.com/lpd/webstore/s...13984541267753

    CCT (Correlated Color Temperature) is a specific measurement form of Kelvin, in this case, the color temperature of a specific bulb at the standard voltage. See how most of the CCT values are in the 2500-3500 range? Notice how this correlates to the yellow section of the spectrum above. Driven at their spec (not overdriven) voltage, this is the color each bulb is expected to produce.



    Practice
    This isn't like the boiling point of water at sea level or the atomic weight of X element. There is no true white, measured or otherwise. What looks white to people only is, because our eyes (genetically speaking) have been looking at light from the sun for many many years. As much as we try to control this with fancy measures, color comes down to simple perception. And what looks white to one person may not look white to another. So selecting a single point that represents all light sources with a single common scale is tough.

    Have a look at the grid of samples below. Each column is one of three flashlights, selected for their nearly neutral, slightly blue, and slightly yellow properties. Each row is a different Kelvin setting on the camera, the color the camera is expecting to see. The result is a tint, representing of how far off (away) from that setting a light source’s color is. Working from my computer screen (and eyes), 4300K is the most representative of what each flashlight is projecting (see Limitations for more information):




    And here are the same three lights, with straight 4300K calibration and photoshop’d exaggerations on either side:





    Method
    In a dark room, shine the flashlight at an (ExpoDisc covered) lens and move it about, adjusting to completely bathe the Disc in even light while being as intense as possible, then take the picture. 1-3 feet away is best, depending on the width of the beam/hotspot being projected. Light blurs to a single color (because of the ExpoDisc) on the way into the camera. F11 is small enough to reduce blotching while still ‘fast’ enough for easy exposure lengths. Shutter speed is light metered (Av - aperture priority) so profiles [generally] have the same brightness (dim lights appear equal to brighter ones), leaving color as the remaining variable.



    Limitations
    • Measurements are based on samples. Incans may change color with age and certainly change color with voltage. LEDs, while more consistent during operation, vary more from unit to unit. The make/model I have may be newer/older than what you have or are considering. Even two LEDs out of the same batch have differences. Binning/sorting minimizes this, but plus or minus 100 degrees K “sees” even tiny variations. Companies improve their products as supplies improve and costs go down. Some of my samples are new, others are 3-4 years old.
    • 4300K is the setting at which these photographs most closely resemble my real world “this is what I’m seeing” experience, but there are no absolutes. 4300K works with my camera and my computer and this file format (JPEG). Were this on a different system (with a different color space like AdobeRGB) or printed on paper, there would likely be a different “standard.” And even then, there are differences in monitor (CRT vs LCD), its calibration (or miscalibration), platform (Mac vs PC), software, and of course us. I double checked my findings with Mrs Guru, who has extraordinary color perception, but even if all your equipment was the same as all my equipment, you may still see differently (and not be wrong).
    • Knowing the simple color of a light does not necessarily predict its ability to render colors. Just because a light source is balanced (ie white), does not mean it also has blue, green, and red components ample enough to reveal colors as well as the sun. The sun produces a broad mixture of energy, including colors (and of those, only some are visible). Some of the efficiency offered by LEDs, for example, comes from the narrow range of colors they produce (not wasting energy on less useful frequencies).



    Notes
    1. All CPF members may use any profile anywhere within CPF and CPF Marketplace. Please contact me directly before using profiles elsewhere.
    2. K stands for Kelvin: The color emitted by a theoretical piece of black material at [given] degrees Kelvin (its temperature). 4300K = 7280.6 ºF. Make iron hot enough and it will glow blue!
    3. Developed to measure the color of hot, glowing objects, the Kelvin scale is very poor at describing the variety of colors now possible with LEDs. There is, for example, no green on the Kelvin scale. Here I use it only to measure the degree/strength of a given color. See post 8 for more information.
    4. All colors presented are darker than actual to enhance viewability, so perfect gray here represents perfect white.
    5. Colors are very much contextual. The background color your CPF profile is set to may effect how the colors appear. Framed in light blue, for example, profiles may appear less blue than they actually are. For highest accuracy, zoom in on a profile or open it up in its own window (right/command-click).



    Extra Reading




    Use
    Here are several familiar (non flashlight) examples to get you started and refer back to later. As you study them (and the profiles below), remember that this is counter intuitive to color rendering ability. Profiles show the 'distance' from white, so the less tinted the source of your light (the closer it is to neutral gray here), the more 'real' the colors of what you are viewing will appear.


























    Last edited by ElectronGuru; 10-28-2009 at 11:26 PM.
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  2. #2

    Default Re: Flashlight Color Temperature Reference


    Bulb & Emitter Profiles














































































    Last edited by ElectronGuru; 05-23-2009 at 10:22 PM.
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  3. #3

    Default Re: Flashlight Color Temperature Reference

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    Flashaholic* Tekno_Cowboy's Avatar
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    Default Re: Flashlight Color Temperature Reference

    Nice Idea :

    I hope this idea catches on. I would be glad to help you add more lights, as I get quite a few through here.

    What would be great is to get someone with a ton of well-sorted led's of the most common bins used in lights, and get them to photo the led's at a given current.
    Due to my current schedule being pretty darn hectic, I will not be accepting new modding projects until things settle down.

  5. #5
    *Flashaholic* greenLED's Avatar
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    Default Re: Flashlight Color Temperature Reference

    Very interesting concept, GE!
    Love seeing this type of innovative ideas on CPF.

    Let me get this straight, these are pics looking into the beam of a light (through the ExpoDisc), right?
    Last edited by greenLED; 05-19-2009 at 10:22 PM.

  6. #6
    *Flashaholic* McGizmo's Avatar
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    Default Re: Flashlight Color Temperature Reference

    What is the color temperature of a green tinted white LED? When a LED is far enough off the planck curve, do you think CCT has much merit?

    Is Green LED warm or cool? (I mean the guy I posted after )
    Build Prices .... some mods and builds (not 4 sale) "Nature can be cruel- but we don't have to be."~ Temple Grandin

  7. #7
    *Flashaholic* greenLED's Avatar
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    Default Re: Flashlight Color Temperature Reference

    Quote Originally Posted by McGizmo View Post
    Is Green LED warm or cool? (I mean the guy I posted after )
    I can be warm and fuzzy, but most of the time, I'm just HOTTT!

  8. #8

    Default Re: Flashlight Color Temperature Reference

    Thanks Guys,

    Quote Originally Posted by Tekno_Cowboy View Post
    I would be glad to help you add more lights, as I get quite a few through here.
    I do only have so many lights and I'd happily add other collections to the lineup. I personally would love adding Ra Lights and more Malkoff's. And of course McGizmo!


    Quote Originally Posted by greenLED View Post
    Let me get this straight, these are pics looking into the beam of a light (through the ExpoDisc), right?
    Correct. The ExpoDisc sits on the front of the lens, and I aim the beam directly through it, into the lens, at the camera sensor. The Disc lets cameras record the ambient color temperature of a room/place for the purposes of calibrating the following shot, by neutralizing/canceling the tint from light sources within that room. Half way through the process, the camera is left with a (normally discarded) image of that tint. This is just a focus on and enhancement of that step.


    Quote Originally Posted by McGizmo View Post
    What is the color temperature of a green tinted white LED? When a LED is far enough off the planck curve, do you think CCT has much merit?
    Great question.

    CCT (K) is linear (two dimensions). Every color measure I can think of (RGB, CMYK, color wheels, etc) is 3+ dimensions, and with good reason. While specific colors translate directly into accurate K values, the opposite is not true - K values do not contain and cannot be translated into specific colors. Here is the greenest light source I have, a simple night light:




    Notice how its K is less than the bluest LED above? I don't have cool matching temp examples, but imagine a pair of lights with the same high K value, one with a green tint and one with a blue tint. And another pair with the same low K value, but one orange and one red. With color, the usefulness of K is as a measure of distance, in this case, showing how far away from neutral (white/gray) a given light source is. In this guide, the color sample itself is the primary tool, the K value only measures a given color's strength (degree of tintedness).

    Edit: Following your question, I've been looking deeper into color rendition. There is some funny thinking going on here. Here's a paragraph from a wonderful article they sheds a bit o light on why:

    Typical phosphor-based white LEDs have color rendering index (CRI) values comparable to discharge lamps (fluorescent and HID lamps). Many people mistakenly believe that a high CRI means high color rendering properties. Actually, the CRI is merely an index of how similar a light source makes colors appear in comparison to a reference source such as incandescent. That's why an incandescent lamp has a CRI near 100. Recent studies show that mixed-color “white” LED systems with a CRI in the 20s can result in higher color preferences than systems with a CRI in the 90s.

    So a high quality LED is 90% as good as an incan (CRI=90) at rendering color, but how good is the incan and how do you measure that? To your original question, the only reason CCT made sense as a description of incan color is because incans only have one color question, "how yellow is it?" Using CCT to describe the variety and complexity of possible LED colors makes only slightly more sense as bringing black and white film to the Rose Parade.
    Last edited by ElectronGuru; 05-21-2009 at 10:56 PM.
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    Default Re: Flashlight Color Temperature Reference

    Great work.

    I was hoping to bring peace in out time to the LED & incan world.
    LEDs should adopt roughly three 'colors'
    3000K warm white (hey that looks like a mini-mag)
    4500K neutral white (it looks like malkoff will have to change that w to an n)
    6000K cool white


    any chance to verify HIR & HID automotive headlights?
    Last edited by MichaelW; 05-20-2009 at 08:15 PM.
    6.5K diving light, 5K cool-white, 4K neutral-white, 3K warm-white, 2.7K extra warm-white

  10. #10
    *Flashaholic* McGizmo's Avatar
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    Default Re: Flashlight Color Temperature Reference

    Electron Guru,

    Since the LED is not a black body radiator, the further from the Planck curve its tint lies, the further from any relevance assigning a CCT to it would have. As you have stated, CRI is also based on black body radiators and keyed to a specific Kelvin temperature. From what I can gather, the CRI number that is typically given is actually an average of perhaps a dozen or more CRI numbers based on the rendering ability of different bands of light. It is posible to have one LED source that has a CRI of 90 that is based on a CCT of 3500k and it is an average of some CRI numbers that are 100 and some that are 80 let's say. You could have another LED that also has a CRI of 90 but it is based on 5500k and all of its constituent CRI values are all 90. The latter LED would likely be much much more acceptable to folks in most color rendering applications and likely appear closer to white when viewing a white surface with it.

    We experience various tints with these LED sources and of course we want a means of quantifying and qualifying them and sorting them. Unfortunately they vary in a "n" dimensional matrix and we seek a one dimensional assignment of number for them or in some cases a single letter designation. Unfortunately their unique position may be so far from the line we want to place them on that we are wasting our time.

    If you look at data sheets from the LED manufacturers you will often find much more information about the LED's and how the bins are defined. It is clear that you can have obvious variations in tint and color rendering ability from samples within the same bin. The x,y coordinates of the color measure allow for a LED to be plotted with some information beyond the planck curve but even then, two LED's can "earn" the same x/y values yet still be quite different in terms of their full spectrum output and distribution.

    It has been my experience that knowing both the CRI and the CCT it is based on has given me the best "feel" for what to expect from a LED in terms of color when I use the LED to illuminate objects of color.

    Because the industry has been involved in incandescent for most of its history, the inclination is to valuate and qualify the LED using the same means and measures. Things are changing but it seems that the marketing arms of the luminaire manufacturers are more than willing to pass on misleading and insufficient information in terms of identifying their wares. What is a warm white LED? What is a cool white LED? The assumption is based on off white tints ranging from yellow to blue as you get cooler yet the reality may involve tints you have never experienced in an incandescent source?!?!

    I am no expert by any stretch of the term and I don't claim to even have a good working understanding of color and the spectrums of light but with the aid of a spectrometer and integrating sphere, I have seen enough to appreciate the overall complexity of the beast and realize that much is lost in any attempt to simplify these light sources by trying to treat them as a black body radiator. Apples VS Oranges or perhaps even more appropriate Cats VS Dogs.

    I would point out that an integrating sphere integrates while a spectrometer differentiates. Some numbers assigned are based on averaging and integrating whereas other characteristics require a two or three or more dimensional matrix to be well defined and identified.

    To quantify a LED source even by CCT and CRI might be no more illusive than qualifying members of this forum by their weight and age.

    Granted we are much more complicated than a LED but the LED has more dimensions than some of us give it credit for.

    4500k is one number and just what does this tell you? In my youth, there was a magic set of three numbers a male might hear on occasion; 36 24 36. Well that was three times as much information but beyond being recognizable to some as to what these numbers related to, it was still insignificant information on any real meaningful level.

    I feel I have thrown a monkey wrench in your endeavor here but I think you can understand my confusion and concern or at least relate to it.
    Build Prices .... some mods and builds (not 4 sale) "Nature can be cruel- but we don't have to be."~ Temple Grandin

  11. #11
    *Flashaholic* McGizmo's Avatar
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    Default Re: Flashlight Color Temperature Reference

    Electron Guru,
    I want to quote here, some of what I am including in an e-mail response I am sending to you:

    "There are members who speak with authority on the lights and yet it is clear to me that they don't really understand the difference between lux and flux. Once you enter the realm of color, it gets way way more complicated!!

    On a white wall, I admit that I have my own color temperature preference (based on black body spectrum) but I understand that a LED source of that color temp may or may not be pleasing to my eye. Once you get into illuminating a full spectrum landscape, I need a whole bunch more parameters to identify in describing my preferred light source and much of it is a guess based on limited understanding and not empirical or measured experience.

    In the real world, I have found that in many cases, flux trumps CCT as well as CRI since sufficient light, across the spectrum may be more important than the actual distribution or spectrum itself. Contrast is also critical and it may or may not have color in its makeup; the distribution of intensity (lux) alone may be at issue.

    Ultimately, my need to understand the light source is back seat to actually using the light source. If I can get the source into the ballpark then I can go about viewing the ball park."

    I admit that these comments are just my take on things and I claim no expertise nor do I consider myself appointed or qualified to speak for anyone else. Whatever floats your boat.
    Build Prices .... some mods and builds (not 4 sale) "Nature can be cruel- but we don't have to be."~ Temple Grandin

  12. #12

    Default Re: Flashlight Color Temperature Reference

    A real world frustration often encountered is the described "warm" LED's which in addition to being "warm" are also an unexpected green. I've found this to be a common fault with incan "replacement" bulbs intended for household use.

  13. #13
    *Flashaholic* greenLED's Avatar
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    Default Re: Flashlight Color Temperature Reference

    Quote Originally Posted by ElectronGuru View Post
    Finally! Proof that my conscience is not black.

  14. #14

    Default Re: Flashlight Color Temperature Reference

    Quote Originally Posted by greenLED View Post
    Finally! Proof that my conscience is not black.
    Thought you might notice that


    Quote Originally Posted by MichaelW View Post
    I was hoping to bring peace in our time to the LED & incan world.
    They're both so much fun, I would be seriously if I had to choose just one. Even forgetting results for a moment, it would be half as much cool stuff to learn and get excited about. Perhaps we can at least calm the waters here.


    Quote Originally Posted by MichaelW View Post
    LEDs should adopt roughly three 'colors'
    3000K warm white (hey that looks like a mini-mag)
    4500K neutral white (it looks like malkoff will have to change that w to an n)
    6000K cool white
    With a few exceptions, these labels are coming out of the marketing departments of LED makers and seem to be relative to older LEDs, not the spectrum as a whole. Malkoff and others probably continue the convention to avoid confusion (rightly so) but some meaning is lost in the process. I'm hoping the presence of a new complete scale will help clear some of our confusion that results, seeing how everything looks relative to everything else.

    +/- 1500 is pretty wide for an ideal. I'm hoping to narrow it down to +/- 1000, something closer to 3500-5500. Part of the challenge is that there seems to be an advantage to a slightly yellow tint. I'm not sure there is a similar benefit to a slightly blue one.


    Quote Originally Posted by MichaelW View Post
    any chance to verify HIR & HID automotive headlights?
    I'll see what I can do.
    Last edited by ElectronGuru; 05-22-2009 at 05:12 PM.
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    Flashaholic* Tekno_Cowboy's Avatar
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    Default Re: Flashlight Color Temperature Reference

    McGizmo:

    While I agree that accurately describing the true output of LED's is very complicated, are you saying that the complexity of it makes this attempt to simplify it pointless?
    Due to my current schedule being pretty darn hectic, I will not be accepting new modding projects until things settle down.

  16. #16

    Default Re: Flashlight Color Temperature Reference

    Quote Originally Posted by Gene43 View Post
    A real world frustration often encountered is the described "warm" LED's which in addition to being "warm" are also an unexpected green. I've found this to be a common fault with incan "replacement" bulbs intended for household use.
    I don't know how typical it is, but I've so far found zero green in your M60W MC-E, just the slightest hint (100K worth) of blue. I've yet to see an LED in the < 4000 range in person.


    Quote Originally Posted by McGizmo View Post
    It has been my experience that knowing both the CRI and the CCT it is based on has given me the best "feel" for what to expect from a LED in terms of color when I use the LED to illuminate objects of color.

    Granted we are much more complicated than a LED but the LED has more dimensions than some of us give it credit for.
    Being much closer to the source end of things, hearing your and Gene's perspective adds greatly to our understanding, thank you both.


    Quote Originally Posted by McGizmo View Post
    Once you get into illuminating a full spectrum landscape, I need a whole bunch more parameters to identify in describing my preferred light source and much of it is a guess based on limited understanding and not empirical or measured experience.

    In the real world, I have found that in many cases, flux trumps CCT as well as CRI since sufficient light, across the spectrum may be more important than the actual distribution or spectrum itself. Contrast is also critical and it may or may not have color in its makeup; the distribution of intensity (lux) alone may be at issue.

    Ultimately, my need to understand the light source is back seat to actually using the light source. If I can get the source into the ballpark then I can go about viewing the ball park."
    I'm working on a color rendition test and will include shadows in the criteria. I agree, whatever the measurement is suppose to reveal, there is no substitute for real testing. Now its a matter of building a test with enough variation to challenge the lights, but with enough stability to be a useful comparison.


    Edit: In recognition of the broader meaning of "color", I am removing "temperature" from the thread's title
    Last edited by ElectronGuru; 05-22-2009 at 08:16 PM.
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    Default Re: Flashlight Color Temperature Reference

    I was thinking long term with a 3000K CCT for warm-white LEDs.
    In the future the LEDs will be so bright... that they will be brighter AND warmer than incans. It seems the harder they get pushed [for more light/efficiency] the white point keeps rising-3500K+
    Well what if you want to keep it warm while having your brightness too (without filtering), then you'd be left with leds {note this time frame might be ten years out}

    and a 6000K CCT is usually the most efficient LEDs, they are for people who like bragging rights, or where the situation requires quantity over quality (if you are old and have a yellowing of the eye)

    and 4500K for the rest of us.

    What ever came of this?
    http://www.led-professional.com/content/view/1038/29/
    It is nice that the granularity is smaller. There are 5 bins between 4500-7000 instead of 4, 4 instead of 3 from 3500-4500, and 6 vs. 5 from 3500-2540.
    6.5K diving light, 5K cool-white, 4K neutral-white, 3K warm-white, 2.7K extra warm-white

  18. #18
    Flashaholic* Tekno_Cowboy's Avatar
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    Default Re: Flashlight Color Temperature Reference

    Quote Originally Posted by Tekno_Cowboy View Post
    McGizmo:

    While I agree that accurately describing the true output of LED's is very complicated, are you saying that the complexity of it makes this attempt to simplify it pointless?
    Reading it over again it looks more like you were just providing information to help make the testing more accurate.

    I think I spent a little too much time out in the sun today
    Due to my current schedule being pretty darn hectic, I will not be accepting new modding projects until things settle down.

  19. #19

    Default Re: Flashlight Tint/Color Reference

    A few tips if you are considering your own ExpoDisc:


    Get the Neutral version, not the Warm/Portrait version.

    Getting the size that matches the filter size of your biggest lens means you can use it on all your lenses. But for purposes here, match the size of your intended lens so you can hold the camera/disc with one hand and light with the other. The focal length you choose is not important. I use a 35mm, but a telephoto should work just as well.

    Learn to take perfectly calibrated, indoor, flash-free photos first to familiarize yourself with how it and your camera work together.


    Be sure your camera allows specific Kelvin settings!

    It appears here (Canon) as Color Temp - 5200K:
    http://a.img-dpreview.com/reviews/Ca...anim_menu1.gif

    Cameras confirmed to have this feature
    Canon 10D
    Canon 20D
    Canon 30D
    Canon 40D
    Canon 50D
    Canon 5D
    Canon 5D Mark II
    Nikon D2H
    Nikon D2X
    Nikon D3
    Nikon D3X


    Edit: It may be possible, shooting in raw, to calibrate to 4300K in software after taking the picture, not needing the fancy camera to do it during shooting.
    Last edited by ElectronGuru; 05-24-2009 at 12:05 PM.
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  20. #20

    Default Re: Flashlight Color Temperature Reference

    Quote Originally Posted by MichaelW View Post
    any chance to verify HIR & HID automotive headlights?
    Two HIDs (thanks Brian!) and two car profiles added (one is both), plus the WA 1111
    Last edited by ElectronGuru; 05-24-2009 at 01:13 PM.
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  21. #21
    *Flashaholic* McGizmo's Avatar
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    Default Re: Flashlight Tint/Color Reference

    Electron Guru,
    If I am following this correctly which is no certainty, I would assume that if you took some shots with your camera (lens covered with the ExpoDisc) of an incandescent source and bracket the shots with manual settings of CCT, as you approached the actual CCT of the light source, the recorded image would approach "white" ? Yes? Or does the image approach the spectrum of color one sees at that color temperature?

    Does the manual adjustment of the camera attempt to filter out the tint and give you a white appearing white surface when you have set the color temp correctly for your light source or does the camera attempt to give you an image of a white surface tinted to match the spectrum of a black body, at that kelvin level?
    Build Prices .... some mods and builds (not 4 sale) "Nature can be cruel- but we don't have to be."~ Temple Grandin

  22. #22

    Default Re: Flashlight Tint/Color Reference

    Quote Originally Posted by McGizmo View Post
    I would assume that if you took some shots with your camera (lens covered with the ExpoDisc) of an incandescent source and bracket the shots with manual settings of CCT, as you approached the actual CCT of the light source, the recorded image would approach "white" ? Yes?
    If we were talking about absolutes from the flashlight, yes it would be white. But in the context of computer displays, there is an extra complication. In nature, when more light is added, it just gets brighter. In a computer, white is already max, so the only way to show bright (accurately) is for everything else to get darker. So adding color reduces the brightness of a given sample. To be on the same K scale as the colors I'm showing then, white has to be darkened to gray.

    Here's an example Mag85 (incan) with a measured color temp of 3500K:




    The left half is what the camera sees, with 21 different K settings, starting with 2500K and ending with 4500K (zero plus or minus 10 whole steps). Down the center is a pure gray reference. Side note: you may notice that at 3500, the actual color is still a tiny bit blue. But 3600K is just a tiny bit red. Even 3550K looks a bit off, the true color the light is putting out is between the two values, but K (expressed in 00's) is not precise enough, so we accept it.

    The right half is what happens when the same values are adjusted so that 3500K is near white. But as you can see, as the brightness reaches the computers ability to display pure white, the colors are almost pure white as well (as we approach maximum brightness, colors get washed out and look rather ).

    So to answer your question, as the CCT approaches the value of the light being measured, the image appears gray.


    Quote Originally Posted by McGizmo View Post
    Or does the image approach the spectrum of color one sees at that color temperature?
    The spectrum is there, but as the goal of this approach is to show the tint, the tint is all you see. With a camera, the only way to show the spectrum of color contained in a light source is with a prism or by shining the light source on something colorful and showing which colors render/reflect.


    Quote Originally Posted by McGizmo View Post
    Does the manual adjustment of the camera attempt to filter out the tint and give you a white appearing white surface when you have set the color temp correctly for your light source or does the camera attempt to give you an image of a white surface tinted to match the spectrum of a black body, at that kelvin level?
    From the point of view of the camera sensor, they are the same thing. Cameras recording light are much simpler than what you have to deal with, coordinating the output of a given LED with the perception of the human eye. Since all the camera needs to do is calibrate to achieve white/gray, a black body radiating at 6000K blue is just as easy to coordinate with as an LED radiating at 6000K green. Configuring the camera to match 6000K will neutralize both tints with equal ease.

    Part of the confusion here is that I have introduced white balance disks at the same time as a new technique that mis-uses them. Normally, they are used to erase tint. Figure out what the tint is and calibrate to it, the camera's K moves about to adapt. Here, I have frozen the K setting of the camera, so the tint is what your actually viewing.

    Think of an ExpoDisc like a grey card, except instead of measuring the reflection of light from a given surface, you are measuring light on what would be, its way toward the grey card. As with a grey card, the goal with using a Disc when taking a photo of something is to match the CCT of the camera to the CCT of the ambient light, so the final photograph appears as though the ambient light was white.

    Ironically, most of this came about because of photographic improvements. Back in the dark ages, we used film. Film was calibrated to sunlight and we used it outside all over the place in natural light. It wasn't sensitive enough to take indoor shots without a flash, so indoor shots were calibrated to a single known source, the flash. And even when color was messed up, someone else was doing the developing and often correcting the color for us. Then along comes digital. Suddenly we are doing everything ourselves, but more importantly, we now have the ability to take indoor shots with ambient light. And as it turns out, the CCT of indoor lighting is all over the place, creating this problem. But I can't stand flash photography, so to me, this is a good problem.

    BTW, here's a good primer on photographic white balancing:
    http://www.ronbigelow.com/articles/w...te_balance.htm
    Last edited by ElectronGuru; 05-24-2009 at 01:39 PM.
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  23. #23
    *Flashaholic* McGizmo's Avatar
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    Default Re: Flashlight Tint/Color Reference

    So to answer your question, as the CCT approaches the value of the light being measured, the image appears gray.
    Thanks that is what I figured. Now if there is any residual tint then I would assume this is due to the light source being viewed having its x,y coordinates off of the Planck curve.

    I believe I am following to a reasonable extent what it is you are doing here but I admit I am not clear as to what is being accomplished but no matter.

    With the integrating sphere and spectrometer I have, I can reasonably integrate the light source (as you are doing with your ExpoDisc) and further I can get a CCT for the source as calculated by the equipment. I could then set my camera at the appropriate kelvin number and photograph the light source through a ExpoDisc and capture an off white (or off gray) image. This would indicate a tint variation or deviation beyond a correction for color temperature, I guess. Now I understand that this exercise would have some significance in regards to the particular sample LED I was working with but as to how well this LED represents other LED's of the same bin or resident in fellow flashlights is still debateable.

    I guess another issue here for me is the fact that our eyes do make adjustments as we acclimate to a light source and I have no idea if we adjust both for color temperature as well as tint or not. My guess is that our personal adjustments can vary from individual to individual and it may not be a simple adjustment based on absolutes or the measures we make with our technical equipment (cameras, light meters, spectrometers, etc.). My gut is that we have our own means of white balance adjustment. Once we do adjust for white balance, we are still dependent on the light source and its ability to render the spectrum of colors out there in the field of view. I know that I personally can't correct to the point that I recognize a purple as a purple if the light source is too far off in its red and or blue output levels. At least I don't think I can but I may not have given myself time to acclimate to a light source and then revisit a purple object.

    We have evolved in the presence of black body sources but who knows how critical it has been in our survival and resultant in our ability to compensate and make perceptual adjustments. We can put on a pair of tinted sun glasses and in no time no longer be aware of the tint. By the same token, we can use a light source that has an obvious initial tint and yet soon be essentially unaware of it. This is particularly true if we use the light source for viewing a range or real world objects and don't limit our focus to a white wall, for instance.

    Beyond our ability to adjust and compensate, a given light source may still fall sort in its ability to allow us the perception we desire. There may be insufficient illumination in terms of overall lux or there may be insufficient light in specific spectral bands (not enough red from a LED or not enough blue from an incandescent).

    When members of CPF express dissatisfaction in a particular light source and attribute it to tint or the perceived warmth or coolness (color temperature) in some cases this is based on white wall observation but often this is based on real world targets and in either case, the member has the right to be dissatisfied.

    Is there some way that we can identify the nature of a light, a member has yet to see, that will aid them in determining whether the light will meet their needs and standards? This seems to be a worthy goal and I suspect part of the intent, with this thread.

    I appreciate your responses to me here and I don't want to sidetrack you any further than I have already.
    Build Prices .... some mods and builds (not 4 sale) "Nature can be cruel- but we don't have to be."~ Temple Grandin

  24. #24

    Default Re: Flashlight Tint/Color Reference

    With the integrating sphere and spectrometer I have, I can reasonably integrate the light source (as you are doing with your ExpoDisc) and further I can get a CCT for the source as calculated by the equipment. I could then set my camera at the appropriate kelvin number and photograph the light source through a ExpoDisc and capture an off white (or off gray) image. This would indicate a tint variation or deviation beyond a correction for color temperature, I guess.
    Since I included numbers to create my scale, its easy to get caught up in them, but relying on them to this degree is making things overly complicated. If the goal is to precisely calibrate a camera to the projected tint, CCT as expressed in hundreds (00's) is not accurate enough. Capturing a CCT, inputting that value into your camera, and then taking a picture based on that CCT is not as accurate as just using the camera's own fully-internal system. Here's another test: Take a sample of a Mag85 with the camera set to 4300 (top), then calibrate the camera (aka, custom white balance) to the first photograph and take a second sample (bottom).




    Running down the middle of both is another reference gray stripe. Measuring the two areas with Photoshop, there is a 1% variance (toward blue). But with my naked eye, I cannot see a difference between the reference gray and the rest of the bottom half. This, compared to the test in my last post shows that using the camera's built in color system is more accurate than setting the camera to 3500K and doing the same thing.

    The larger point here is that everything I am doing here is about photography, visually recording what the bulbs and emitters are doing. Trying to use this qualitative measure as a quantitative one will quickly exceed the capabilities of the camera. In both cases, any variance from true color is about the limits of the camera/settings, not a deviation of the bulb.


    We have evolved in the presence of black body sources but who knows how critical it has been in our survival and resultant in our ability to compensate and make perceptual adjustments. We can put on a pair of tinted sun glasses and in no time no longer be aware of the tint. By the same token, we can use a light source that has an obvious initial tint and yet soon be essentially unaware of it. This is particularly true if we use the light source for viewing a range or real world objects and don't limit our focus to a white wall, for instance.
    Anecdotally, I would attribute this to the same biological tendency we have to smells or sounds. We are relativistic beings, so adjustment to new 'normal' is necessary if we are to perceive a new 'different'. It would badly suck, for example, if when the sky got twice as bright, we could no longer see traffic signals. Being unable to perceive absolute [anything] is a small price to pay for these abilities.


    When members of CPF express dissatisfaction in a particular light source and attribute it to tint or the perceived warmth or coolness (color temperature) in some cases this is based on white wall observation but often this is based on real world targets and in either case, the member has the right to be dissatisfied.
    I agree. The trouble with numbers is that they are abstract. Just as we understand graphs more completely and easily than a table of numbers, having to imagine what 3300K looks like is also an obstacle to understanding. My hope is that by showing a color, alone and in context with other colors, that we can more easily imagine what it looks like and predict its performance.


    Is there some way that we can identify the nature of a light, a member has yet to see, that will aid them in determining whether the light will meet their needs and standards? This seems to be a worthy goal and I suspect part of the intent, with this thread.
    The problem is actually one of labor. Were it practical, you could just profile every emitter in every light before sale and every customer would know what they are getting. But this is impractical even with a small volume. In your case, if a given bin was narrow enough in color/render variation, we could show sample performance for that bin and people viewing that sample would know what to expect. If not, we would either show the variation possible in a bin (map the lottery) or create our own more accurate bins.
    Last edited by ElectronGuru; 05-25-2009 at 11:31 PM.
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  25. #25
    Flashaholic* ANDREAS FERRARI's Avatar
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    Default Re: Flashlight Color Temperature Reference

    Quote Originally Posted by McGizmo View Post

    There are members who speak with authority on the lights and yet it is clear to me that they don't really understand the difference between lux and flux.
    I agree-CPF has more then it's share of members who are either delusional or have a high level of self-importance.

    ElectronGuru-despite the number of valid concerns about your project I have to applaud your creativity.I always appreciate it when someone comes up with a new concept instead of just doing 'more of the same'.
    My girlfriend said if I bought one more light she would leave me...........I'm sure gonna miss her.

  26. #26

    Default Re: Flashlight Tint/Color Reference

    I confess I get lost every time I read one of these color threads. This is NOT helping with my sense of self-importance.

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  27. #27
    *Flashaholic* Patriot's Avatar
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    Default Re: Flashlight Tint/Color Reference

    Quote Originally Posted by souptree View Post
    I confess I get lost every time I read one of these color threads. This is NOT helping with my sense of self-importance.

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    You're not alone!

    I know this is going to be helpful to me in some way but after the first read through it's mostly above my head. There are obviously one or two base concepts that I'm unable to wrap my brain around. For example I'm looking at the charts and they're telling me what white is but yet I look at the actual web page where the text is and it looks "whiter" to me than any of the chart examples. I'm going to have to go through this all again.

    Thanks for the thread E.G. It looks like you've put a lot of thought and work into it.

  28. #28
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    Default Re: Flashlight Tint/Color Reference

    I just came across this thread and I'll agree it's going to take a while to wrap my head around exactly what is being done here. My interpretation (and correct me if I'm wrong) is that a light is shined at a neutral background (meaning it returns all colors equally), and the camera's Kelvin setting is adjusted in 100K increments until the color of this neutral background appears gray. The Kelvin setting where the background appears gray (grey for those on the other side of the pond) is the CCT of the light source. The best way to determine when the background truly appears neutral would not be by eye, but rather when the red, green, and blue components are equal. In practice this may not always be possible if the light source lies outside the black body locus. In that case, the closest shade of gray must be determined by eyeballing it.

    I really need to take some time to reread this entire thread and digest it before commenting further. I just wanted to make sure I'm interpreting the basic methodology correctly.

  29. #29
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    Default Re: Flashlight Tint/Color Reference

    As much as I decry subjective information, and long for good objective info here on CPF, I am in a quandry about this whole issue about tint/color. I am now thinking that what I see and what others report about what they see, relative to color and tint reflected by an LED or and incan light, is more important than so called objective info as offered by the OP or others. In effect, let my eyes, or your eyes, do the telling. For simple old me, I can go with LEDs in the daytime and incans at night, and so what about CRI and CCT.

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  30. #30

    Default Re: Flashlight Tint/Color Reference

    Quote Originally Posted by Patriot View Post
    Thanks for the thread E.G. It looks like you've put a lot of thought and work into it.
    I thought about it in my head for nearly a year, then developed the actual process over two months. So if you want to understand the theory/process (optional), its going to take a bit to catch up, but I think its worth the trip.



    Quote Originally Posted by jtr1962 View Post
    My interpretation (and correct me if I'm wrong) is that a light is shined at a neutral background (meaning it returns all colors equally), and the camera's Kelvin setting is adjusted in 100K increments until the color of this neutral background appears gray.
    Don't overthink this, its simpler than it looks. The 100K increments are not used in creating the finished samples, that is only explaining the the process behind the results, sort of like "showing my work" in a math class. At no point is reflection taking place. At no point is the color of any object coming into play with these measurements. Here's a view of the physical steps:


    ONE, setup the camera as a target for the flashlight



    TWO, place the expodisc in front of the lens (this is the thing that blurs the light



    THREE, shine the light source at the target (camera)



    FOUR, take the picture


    The light and color of the light is recorded directly by the camera. The disc does not modify the color in any way, it only smoothes it out (makes all parts of the image the same light/dark'ness) so that the sample is easier to view.

    Think of a camera set to 4300K as a pure representation of our eyes perception of color. Once set, anything that looks yellow to the eye will look yellow to the camera and anything that looks blue to the eye will look just that much blue to the camera - and in the resulting photograph. Point the configured camera at light that looks green to you, the photo will be green. The complicated part was getting the camera to mimic the eye. Now that its there, the results *should* be nearly intuitive. We've just got all these numbers confusing everyone.


    Quote Originally Posted by Bullzeyebill View Post
    I am now thinking that what I see and what others report about what they see, relative to color and tint reflected by an LED or and incan light, is more important than so called objective info as offered by the OP or others.
    Our eyes weren't build to measure, they were built to perceive. The camera and photos it produces are accurate perceptions - its the K #'s themselves that are limited to black body representations. I wish I had left Kelvin values off my samples, instead of helping folks relate to what they already knew, the numbers have only confused and obscured what I want everyone to see:

    The color in a sample picture is not constructed. Its what the camera actually sees/records and is all you need to look at to intuitively understand the color of the light that a given light source is producing.


    Anyway, thank you guys for having the courage to speak up. This gives everyone a chance to learn more.
    Last edited by ElectronGuru; 07-19-2009 at 02:16 AM.
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