Excuse the extreme geeking out in this thread. I feel like I am excused since this is the "brew science" section.
I'm suprised I haven't read through this material before. After all, I am a Color Management Specialist at a printing company.
When I first heard about SRM, I immediately realized what the links in this thread
(especially the second one
) say abou the limitations of SRM. In printing terms, SRM most closely resembles how we measure the whiteness of paper. Whiteness is a measure of the reflectance of light at 457nm by a spectrophotometer. In these terms, SRM is merely a factor of how light passes through a beer.
In the printing industry, we have color viewing and measurement standards. We obviously have a much wider range of colors to describe. In general, a three value system is used to quantify numbers. Most people and programs use L*a*b* color space
. I find the CIE LCH system more intuitive. Basically it describes color according to lightness, chroma and hue. Lightness is how light or dark a color is. Chroma is how saturated it is. Hue is the actual color.
To measure beer color correctly one would need to do a flow cell analysis. Sorry no link. I forget what the instrument is called since I haven't used one since my Junior year in college. This instrument is used to measure the pure color of ink. You dillute the ink at a certain rate. You pour it into a system that feeds it into a very thin clear tube. A spectrophotometer then reads the spectral data.
I believe the very same instrument and software could be used to very accurately measure the color of beer. I am willing to bet that a certain large brewery uses a very similar method so their extremely pale lagers all come out the same color. If not, I need to put in my resume!