Turns out that this stands for color rendering index and one tool you need to figure it out is a spectrometer... but that sounded expensive.
A bit of Googling, however, drops you into this web page (spectralworkbench.org/capture). It's a web based program... nothing needs to be installed, other than a Chrome browser and a USB webcam
This is a web based program that allows you to get power-spectral-densities (sounds fancy! but it's just a program which looks at a spectral line and computes its intensity).
The spectrometer, however, is just created out of a paper template and it is very hard to get repeatable results. A better approach is to use something a bit more stable... in this case wood.
A spectrometer is nothing more than a tiny window slit, a diffraction grating and a view port in a box. The diffraction grating can be made from a DVD. The slit can be made with some metal tape, and the view port can be a USB web cam.
After building a simple box (dimensions don't seem to be too critical, mine is 8" x 2.5" x 2.5"). A slit on one end needs to be created with metal tape (it's in the furnace repair section of a hardware store):
The camera needs to be a close focus. I bought a bore scope (design for inspecting plumbing and such on ebay). Other option is to buy a web cam and take it apart. The lens needs to be refocused for close in work. Google "endoscope usb" and don't pay more that $16.00! (some come with 15 meters of cable which is not needed)
Next challenge is to understand how the specctra relates to CRI