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View Full Version : CCT and LEDs: color filters vs. phosphor coatings


irrig8r
04-27-2012, 10:58 AM
Thoughts about color filters vs. phosphor coating? Which is going to hold up better over time?

Pros? Cons?

http://www.fxl.com/products/document...5231991997.pdf

http://www.fxl.com/products/documents/13034212551271276.pdf

http://www.fxl.com/products/document...1262669491.pdf

One thing I notice in the specs is that these seem to have a minimum voltage input of 10V.

INTEGRA Bespoke Lighting
04-29-2012, 09:39 PM
Hi Gregg. I can explain all of this much better on the phone than I can here, and also a more efficient use of my time. Please give me a call on Monday when you have some time. (my cell would be best)

Regards

steveparrott
04-30-2012, 10:16 AM
Hi Gregg. I can explain all of this much better on the phone than I can here, and also a more efficient use of my time. Please give me a call on Monday when you have some time. (my cell would be best)

Regards

James, I think the whole community would like to hear your thoughts on this excellent question.

steveparrott
04-30-2012, 06:08 PM
In response to this question of using color filters vs. phosphor coatings, a pHD LED development engineer (tops in the field) had this answer:

"Color filters are subtractive. That is they can only remove light generated by the LED. This is an extremely inefficient, and in my view, counter-productive way to achieve a desired CCT (Correlated Color Temperature). It is the light equivalent of cutting off your left arm to lose weight! It is very misleading to suggest that adding color filters accurately adjusts CCT.

It should also be noted that the use of color filters greatly diminishes CRI (Color Rendering Index). CRI refers to how well colors of objects are reproduced compared to standards. The filters enhance the primary colors: Red, Green, Blue, Yellow. But they do this by sacrificing a substantial portion of the other colors by absorbing them! They also sacrifice the efficiency of the LED. According to the definition of CRI all colors of the visual spectrum are taken into account, so the TRUE CRI would be very low since the other colors have been removed; e.g., a Yellow filter throws away some or all of the LED light generated in the Red, Green and Blue part of the spectrum.

It would be vastly superior to use white LEDs of the particular color temperature to generate the desired light. For example, using such (red) filters might make a red flower "pop", but the blue ones would look very dull indeed! The overall scene would sacrifice one color in favor of another, all the while tossing away any semblance of energy efficiency."
The engineer went on to explain (in very complex terms) that the use of color filters actually negates CCT determination. According to the CIE (group that defines CCT), you can only determine CCT when the light source lies near the plankian (black body) locus. All white LED's are (by definition) located near this locus. Light sources that have color tints (such as produced through color filters) are distant from the locus - they're no longer white sources. They may visually approximate a certain CCT, but they will not render colors in the same way as will white sources at that CCT.

INTEGRA Bespoke Lighting
04-30-2012, 06:11 PM
Yep, I would agree 100% with that information.

S&MLL
04-30-2012, 06:16 PM
In response to this question of using color filters vs. phosphor coatings, a pHD LED development engineer (tops in the field) had this answer:

"Color filters are subtractive. That is they can only remove light generated by the LED. This is an extremely inefficient, and in my view, counter-productive way to achieve a desired CCT (Correlated Color Temperature). It is the light equivalent of cutting off your left arm to lose weight! It is very misleading to suggest that adding color filters accurately adjusts CCT.

It should also be noted that the use of color filters greatly diminishes CRI (Color Rendering Index). CRI refers to how well colors of objects are reproduced compared to standards. The filters enhance the primary colors: Red, Green, Blue, Yellow. But they do this by sacrificing a substantial portion of the other colors by absorbing them! They also sacrifice the efficiency of the LED. According to the definition of CRI all colors of the visual spectrum are taken into account, so the TRUE CRI would be very low since the other colors have been removed; e.g., a Yellow filter throws away some or all of the LED light generated in the Red, Green and Blue part of the spectrum.

It would be vastly superior to use white LEDs of the particular color temperature to generate the desired light. For example, using such (red) filters might make a red flower "pop", but the blue ones would look very dull indeed! The overall scene would sacrifice one color in favor of another, all the while tossing away any semblance of energy efficiency."
The engineer went on to explain (in very complex terms) that the use of color filters actually negates CCT determination. According to the CIE (group that defines CCT), you can only determine CCT when the light source lies near the plankian (black body) locus. All white LED's are (by definition) located near this locus. Light sources that have color tints (such as produced through color filters) are distant from the locus - they're no longer white sources. They may visually approximate a certain CCT, but they will not render colors in the same way as will white sources at that CCT.

I concur Steve haha!

David Gretzmier
05-01-2012, 02:31 AM
I think the answer lies somewhere in the different approach of the different LED bulb manufacturing methods out there.

phillips uses a straight blueish white LED with no phosphor coating on the LED lens. This throws a lot of lumens per watt. it then creates a bulb using a plastic "filter" of yellow with a tinge of green to take the blue colored LED to a warmer white. the bulb looks yellow, turn on the power, it looks white. but the yellow absorbes many of the lumens per watt gained.

other manu's seem to be going the other route- take a warm to cool white LED from the factory that has a yellow green phosphor over the LED lens, and then use frosted white for the plastic "filter". the bulb thus looks "normal colored" when off. you sacrifice some lumens per watt on the phosphor, but don't lose so many through a frosted glass or plastic cover.

which is right? time will tell which will give you a better color and efficiency. my guess is both phosphor and yellowed colored plastic will fade over time. and these bulbs are rated to last a LONG time. so a bulb with a color temperature of 2700k today might be somewhat different at 10,000 hours or 30,000 hours. again, time will tell and we will learn as we go. it took decades of improvement to get the incan, halogen, fluorescent, HPS and Metal halide where they are to today.

Duekster
05-01-2012, 04:25 AM
One thing I notice in the specs is that these seem to have a minimum voltage input of 10V.

That is - 20%