Ask the Expert Question-and-Answer Archive

by Ron Joseph

June, 2006

FED-STD-595 Matching

Q. Is there a standard to approach to matching surface colors to the FED-STD? Since the color we're intrerested in is a fluorescing material, is natural north sky the best approach?

A. Your email was forwarded to me by Mr. Ron Joseph.

I understand you want to match one the six FED-STD-595B fluorescent patches on page 49 of the standard.

Ideally, a match should be done under the light source(s) which will be used to view the product in normal use. This is particularly important for fluorescent colors since the the Ultra-Violet (UV) content of each light source, which causes the fluorescence, can vary tremendously from one source to the other.

Your mention of "natural north sky" makes reference to North Sky Daylight, or Illuminant-C; I therefore assume that the product will be used in daylight. Please note hat Illuminant-C has been superseded by D65. The problem is not so much the difference between Illuminant-C and D65 which, while measurable, is nothing compared to the differences between real daylights corresponding to various sun positions (time of day and latitude) and atmospheric conditions.

For critical comparisons, I recommend, in order of decreasing preference, to:

a- use a light-booth set at D65;
b- when available, use a spectrometer/colorimeter which has a D65 filter on its lamp;
c- use a spectrometer/colorimeter, with no UV filter, based on a xenon flash lamp;
d- use a spectrometer/colorimeter, with no UV filter, based on a tungsten lamp.
e- If you do not have access to any of the above instruments, make your comparison with natural daylight, facing North, around noon, on a clear day. If the comparison is done inside, open the window so that there is no glass between the sky and the sample (i.e. window glass absorbs UV), and close the room lights.

In "a" and "e" above, the visual inspection has the additional advantage that gloss effects can also be taken into consideration by the person making the comparison, if gloss is important for your application, of course. A gloss meter could also be used to complement any instrument-based color comparison.

Best regards,

Danny Pascale