" Will Somebody Please Set Me Straight On This?"

Hi Everyone on board -

I think I have a general idea but would like to hear it from somebody who really knows. What does 4300, 6000, 7000 mean when the conversation is about the "color/" or "temp?" (pardon me if I am incorrect on either of these) of the beam of light being produced by an HID bulb or LED, etc. In trying to compare for instance the Oracle and Tactical 35W HID lights, I see that the Oracle uses a 6000 bulb wheras the Tactical uses one at 4300. Is one brighter than the other, does it throw further or is it just that the color of the lightbeam appears different in each one? I think I have grasped it by reading thru some of the various threads here but would like somebody to say it in layman's language for me if that isn't asking a bunch? Thanks to anyone who jumps in here with an answer.................

Light Me Up Scotty..........Terry

The numbers are degrees on the Kelvin scale. Natural daylight (at noon) is approximately 5500K. Values greater than daylight trend towards blue. Value less than daylight trend toward red.

You'll find a decent picture of the white color scale here.

Paradoxically, a higher color temp is actually referred to as a "cooler" tint, not a "warmer" one. I believe bulbs around 4300K are brighter because they are originally manufactured as this color temp, and dyes are applied to the bulbs to make the tint more blue. Naturally, this gets rid of some of the light, making it dimmer. A 4300K bulb will throw more (in the same reflector, of course) than a 6000K or 8000K bulb because there is more light. Also, since many things outside (such as trees and the ground) are greener and browner, a light with more yellow (such as a warmer tint) would theoretically be reflected more by those objects, resulting in more throw.

TOQ said:

Hi Everyone on board -

I think I have a general idea but would like to hear it from somebody who really knows. What does 4300, 6000, 7000 mean when the conversation is about the "color/" or "temp?"

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They are the temperature of a dark body (A lump of metal can be used as a substitute), this body will emit light. A incandescent bulb is usual a bit below 3000, the sun is on a clear day is about 5600. A high temperature (5000+) will look blue and a low temperature (4000-) will look red, but this color cast will depend on the circumstances, our eyes are very good at ignoring it.

HKJ said:

They are the temperature of a dark body (A lump of metal can be used as a substitute), this body will emit light.

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Yup, so dark that it is completely black body (radiator) :nana:

Black body radiator is an idealized object, as many things in physics, but some real objects (e.g. the Sun, HKJ's lump of metal or an incan bulb) have the emission spectrum quite close to it. For other objects, like LEDs, the spectrum is importantly different but to confuse consumers (or use the terms that they may already be familiar with) manufacturers use the notion of the color temperature to describe also the LEDs. It is called the correlated color temperature (CCT) i.e. a temperature of black body radiation that would have a vague "similarity" to what the emitter actually emits.

wapkil said:

Yup, so dark that it is completely black body (radiator) :nana:

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I was a bit to quick with the answer

HKJ said:

I was a bit to quick with the answer

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To be fair, I think it's not completely incorrect. IIRC sometimes a term "gray body radiator" is also used to describe (I think) real objects with the emission close to the black body. So some radiators are actually darker than others

Thanks to all who have responded to my question so far. I happen to prefer a really white light beam so I am thinking that I should be looking in the 5000 to 6000 range to achieve this according to the graph. Looks like the Oracle would be the light of choice for a 35W HID as the Tactical unit is a bit below that range at 4300. I am not going to jump in just yet but am going to wait a bit longer to see if any other mfgrs release a high powered HID light utilizing a bulb in the 5500 range, one that to me would seem almost "perfect" by my standards. Thanks again, I learned something here for sure............

Light me up Scotty............Terry

Mjolnir said:

Paradoxically, a higher color temp is actually referred to as a "cooler" tint, not a "warmer" one. I believe bulbs around 4300K are brighter because they are originally manufactured as this color temp, and dyes are applied to the bulbs to make the tint more blue.

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Not true with HID. In the case of incandescent lamps, blue tinting is used to change the ~3000k intrinsinc output of the lamp to a more "white" appearing ~4000k color. This is what headlamp replacements such as the Sylvania Silverstars use -- a blue filter coating.

In the case of HID lamps, the color is determined by the materials included inside the lamp, which emit different colors when exicited by an electrical arc. A lamp with a mercury fill-gas alone will tend to emit a bluish white spectral output. Introducing different gases or Salts (Metal halides) can be used to change the color, as different materials tend to emit different colors. There isnt' really any filtering going on.

The reason the 4300k appears the brightest, in genreal, is because the human eye is most sensitive to green light. 4300k lamps have the highest percentage power output in the green portion of the spectrum where our eyes work best. high color temps tend toward more blue, lower color temps tend toward more red. In either case, the lumen output is usually lower.

I think what I heard only applies to car headlights then... Apparently the factories only make car headlights in the 4300K range.
So then do all of the HIDs actually have the same lumens, but some appear brighter? Or do the warmer tinted ones actually output more overall visible light? It has seemed to me that it is the latter, but it seems like you are saying it is the former (then why aren't warmer tinted LED's considered "brighter?").

Mjolnir said:

I think what I heard only applies to car headlights then... Apparently the factories only make car headlights in the 4300K range.
So then do all of the HIDs actually have the same lumens, but some appear brighter?

Or do the warmer tinted ones actually output more overall visible light? It has seemed to me that it is the latter, but it seems like you are saying it is the former

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Lumens = apparent brightness.

The definition of a lumen is optical power (in watts) weighted by the human eye sensitivity to the emitted colors. This is easiest to undersand if you consider that a UV or IR light source, no matter how "bright" in terms of output power will always have a lumen output of 0 because it is invisible to human vision. See: http://en.wikipedia.org/wiki/Luminosity_function/

Various HID lamps should typically have close to the same optical power output as each other. But the eye is more sensitive to some than others, causing there to be a difference in lumen output.

(then why aren't warmer tinted LED's considered "brighter?").

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LEDs do not operate the same way. A bare blue LED for example emits blue light with fairly high efficiency. So it will have the highest amount of optical power output. However, because our eyes are not very sensitive to this blue light, the bare blue LED will have fewer lumens than a blue LED with a phosphor on it (eg a white LED).

Adding a phosphor to this blue LED to make a white LED will reduce optical power output (eg the conversion of blue to other colors in the phosphor has some losses). However up to a certain point this will be more than offset by the human eye's higher sensitivity to the white light than plain blue light.

However, if you attempt to make the white LED warmer by using a thicker layer of phosphor, at some point the conversion losses in the phosphor will beocme a more dominant effect than the efficiency gained by using more yellow-green light that the eye is more sensitive to. This is not necessarily true in other light sources, such as HID. If a perfectly lossless phosphor were to be used in all cases, the warmer LEDs (read: 3500-4500K color temp) would actually appear brightest. But because of the use of lossy phosphors, cooler white LEDs (5500k or so) appear the brightest.

thanks for posting this and thanks to all who replied.

Why are the units of color measurement presented in degrees Kelvin?.. thats a measure of thermal temperature... not color.

Shouldn't units of color be measured on a spectral frequency... Like audible sound=Hertz or radio waves=Mhz. :thinking:

I believe it has to do with the temperature of "black body radiators," which is what others were talking about above. When these "black bodies" certain temperatures, they theoretically give off certain wavelengths of light (sort of like a piece of metal glowing if you heat it up enough).
These lights do not give off one single wavelength, so you can't measure them in nm, like with lasers.

kramer5150 said:

thanks for posting this and thanks to all who replied.

Why are the units of color measurement presented in degrees Kelvin?.. thats a measure of thermal temperature... not color.

Shouldn't units of color be measured on a spectral frequency... Like audible sound=Hertz or radio waves=Mhz. :thinking:

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"white" light generally follows a blackbody distribution. You can see a demo of this with this Java Applet

Temperature of a blackbody radiator, and peak spectral wavelength are directly related to each other by Wien's Law:


b = 2.8977685(51)×10−3 m·K

So for example, at 6000K, the peak wavelength emitted is 480nm (blue). At 3000K, peak emitted wavelength is exactly double at 960nm (IR)

Here are a couple of colour charts to give you an idea of what the different colour temperatures look like.
These are Cree charts so you can also get an idea of what a Cree bin (WC or 5A) means. (I lost all my bookmarks so I cannot link you to the master thread with the charts of all the manufacturers).