# Changing the Color Temperature of Light [closed]

Suppose I have a lamp that produces light at 5,5000 k. I need to play around with the color temperature and change it up and down (4,000 k, 6,000 k etc) at will. Based on my research, I believe there are "light filters" available that could change light from one color temperature to another.

My questions are:

• Is there lumen loss when doing so & is there a formula to calculate it?
• If yes, does it matter whether we are attempting to increase the color temperature (say from 5,500 to 6,000 ) or decrease it (say from 5,500 to 4,000 )?
• From a scientific perspective if light is simply electromagnetic waves vibrating at a specific wavelengths how is it possible to transform light from one wavelength to the other? Are the light waves being absorbed by the filter at one wavelength and then being remitted at the other?

## closed as off-topic by Mo_, Bill N, knzhou, Daniel Griscom, YashasOct 1 '17 at 4:06

This question appears to be off-topic. The users who voted to close gave this specific reason:

• "This question appears to be about engineering, which is the application of scientific knowledge to construct a solution to solve a specific problem. As such, it is off topic for this site, which deals with the science, whether theoretical or experimental, of how the natural world works. For more information, see this meta post." – Mo_, Bill N, knzhou, Daniel Griscom, Yashas
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• What kind of light are you using? Is this a light that you might be able to actually change the temperature of (such as an incandescent light bulb)? – Cort Ammon Sep 12 '17 at 16:38
• You might want to look at the background to the GE Reveal technology, like here. They are changing the color of the light - not actually the color temperature, just taking out some of the yellow. But the effect is pretty striking - the light definitely looks "whiter". – Floris Sep 12 '17 at 17:46
• 55000 K is extreme ultraviolet or Röntgen... maybe you wanted to write 5500K, it is yet nice. – peterh Sep 24 '17 at 9:28

Is there lumen loss when doing so & is there a formula to calculate it?

Yes. A filter can only absorb light, not increase it.

The formula is unfortunately not simple. It would relate the absorbtion spectrum of the filtter with the emission spectrum of the lamp, weighted by the (standardized) sensitivity spectrum of the human eye.

From a scientific perspective if light is simply electromagnetic waves vibrating at a specific wavelengths how is it possible to transform light from one wavelength to the other

A lamp doesn't just produce one wavelength. It produces a wide range of wavelengths with different amounts of power in each one (characterized by a spectrum). For an incandescent lamp, the spectrum will span the entire human visible range, and well into the infrared (and a bit into the ultraviolet). This will more-or-less approximate the emission of a black-body radiator with a certain temperature. The color temperature tells us what temperature black-body this lamp most closely approximates.

Your color-temperature conversion filters will reduce the power in some wavelengths while passing power at others to try to make the output approximate the spectrum of some other temperature of black-body. It won't be able to create power at wavelengths where the lamp didn't produce it, and it won't be able take power in at one wavelength and output it at another. There are devices that can do this, but they don't act equally on wide ranges of wavelengths, so they aren't much use for this kind of application.

If your lamp is a fluorescent bulb or an RGB LED system, things get more complicated, and a temperature conversion filter that is meant for incandescent bulbs might not give good results when used with these source, or vice versa.

That said, temperature conversion filters are likely to be available for common cases like trying to make fluorescent light look more like sunlight. This is (or was before digital photography became the norm) a very common filter available for photographers.

Is there a lumen loss?

Filters work by attenuating some wavelengths. The amount of light that comes out of a filter will be less than the amount that went in no matter how you define "amount."

Does [the lumen loss depend on] whether we are attempting to increase the color temperature [...] or decrease it?

Nope. Either way, A filter only works by attenuating some wavelengths.

how is it possible to transform light from one wavelength to the other?

Filters don't do that, but there is another phenomenon called fluorescence that you might want to read about.

Are the light waves being absorbed by the filter at one wavelength and then being remitted at the other?

Photons that are absorbed by a filter are not re-emitted. Their energy increases the temperature of the filter.

Photons that are absorbed by atoms/molecules in a fluorescent substance temporarily raise the energy of electrons in the material. The electrons give up some of that energy by emitting new photons of longer wavelength.