Is it possible to give a color temperature for light that has been filtered?

At work we have a clean room with yellow light that has been filtered to remove blue and UV components because we process photosensitive materials there.

Now our safety inspector asked me to specify the color temperature used and I am wondering whether it is at all possible to give one for such lighting. My understanding is that color temperature is the spectrum of light emitted by a black object when heated to a certain temperature. And no black object will emit a partial spectrum. But as I am not sure my grasp on the physics is correct I want to know:

Is it possible to give a value and which would it be for white light with the UV to blue bands (everything < 500nm) filtered out?


Is it possible to give a color temperature for light that has been filtered


The color temperature value of a light source refers only to the visual appearance of the source, but does not necessarily describe the effect this source will have on photographs or photomicrographs. Also, color temperature does not take into consideration the spectral distribution of a visible light source.

In cases where a light source, such as a fluorescent lamp, laser, or gas lamp, does not have a spectral distribution similar to that of a black body radiator, its color temperature alone is not a reliable means of selecting suitable filters for color balance corrections. Therefore, although two different light sources may be described as having the same color temperature, exposed photographic emulsions may respond differently to the sources.

When using fluorescent lamps or similar light sources, a per-wavelength comparison of film sensitivity and spectral output is necessary to determine the correct filters for color temperature balance.

So if you are using two measured light sources you add their color in mireds instead of Kelvin.

From Wikipedia: https://en.wikipedia.org/wiki/Color_temperature#Approximation

If a narrow range of color temperatures is considered—those encapsulating daylight being the most practical case—one can approximate the Planckian locus in order to calculate the CCT in terms of chromaticity coordinates.

See AGI's webpage: "All Things Lighting" for an example.


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