Appropriate Illuminant/Observer Choice for WalMart White LEDs at 4000K

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FAQ: "We are working with Walmart on a project where they are outfitting their store with LEDs bulbs 4000K, 90CRI. I know our LabScan XE uses a pulsed xenon lamp but is there an illuminant selection I can choose that will provide me with the same spectral output as these 4000K white LEDs?"

The spectral output of the lamp in the instrument is not an issue in the illuminant selection to match an LED bulb of 4000K color temperature and 90 CRI color rendering index.

The lamp in a colorimetric spectrophotometer just has to be a bulb with a full spectrum white output in the visible spectrum with an optimal output from 360 nm to 780 nm (400 nm to 700 nm acceptable). Tungsten lamps, pulsed xenon lamps, steady xenon lamps, white LEDs - all instrument lamps are acceptable if they meet that criteria. The only instruments that would not qualify would be a tristimulus colorimeter and an LED that is made from multiple colors LED lights (not single white LED).

When you standardize an instrument with a white tungsten lamp, or pulsed xenon, or white LEDs, the spectral output of the instrument lamp is set to known values of 0% reflectance using the black glass and 100% reflectance using the white tile, at every 10 nm across the visible spectrum. This negates any differences in the spectral output of the white lamp source. You then measure your sample to determine it's unique spectral signature relative to the bottom and top-of-scale.

The purpose of the illuminant/observer is to attenuate the color values calculated from the spectral reflectance of the sample to reflect what the sample color would look like under that type of white light.

The CIE has yet to define any illuminants to match LED lamps -   [CIE Illuminants for White LEDs](https://support.hunterlab.com/hc/en-us/articles/203928055-CIE-Illuminants-for-White-LEDs).

The CIE are working on this issue but the wheels turn slowly...

As for selecting an illuminant/observer to match the lighting output of a Walmart store with LEDs bulbs of 4000K, 90CRI, the following would be the standard options for users of color measurement equipment:

Use F11/10 representing a narrow tri-band fluorescent of 4000° Kelvin color temperature.
Use D65/10 representing 6500K color temperature as being a good default choice.

Another alternative would be to contact Walmart and, given that that the CIE has not defined illuminant/observer tables for white LED sources, if they can supply a custom illuminant/observer table for their 4000K LED/10 (spectral 10 nm data), we can help you implement it.

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