ElectronGuru
Flashaholic
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 :thinking:
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/searchbylamp.tpl?SKU=17345948104771&cart=12413984541267753
http://www.walamp.com/lpd/webstore/searchbylamp.tpl?SKU=17345948104771&cart=12413984541267753
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
- All CPF members may use any profile anywhere within CPF and CPF Marketplace. Please contact me directly before using profiles elsewhere.
- 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!
- 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.
- All colors presented are darker than actual to enhance viewability, so perfect gray here represents perfect white.
- 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
Degrees K color temp explained
Thoughts on colour perception
Spectrographic charts
List of LED flashlights ~4000K
Does Lower LED temp equal better Color Rendition?
Thoughts on colour perception
Spectrographic charts
List of LED flashlights ~4000K
Does Lower LED temp equal better Color Rendition?
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.
:devil:
Last edited: