Sekonic C-800
The Sekonic Spectrometer C-800 is a full-spectrum color meter that can precisely measure every kind of light including LED, HMI, Fluorescent, and electronic flash. Its high-resolution measuring system featuring a CMOS sensor enables capturing spikes in light source output to provide unsurpassed color measurement accuracy.
It has CRI, TLCI, TLMF, TM-30-18, CRI, and SSI. The meter will give you any lights (x, y) values to measure precise chromaticity coordinates, and you can measure Hue and Saturation.
Each of these indexes are designed to allow you to compare multiple lights against each other.
This information was gathered from this video:
CRI
Based upon the evaluation of 8 colors, using the human eye as the observer. The first 8 colors are what the Ra or CRI score is based on. There are additional colors, R9-R15 which are also there for further evaluation.
Measured from 0-100 85-95 is seen as good over 95 is exceptional
They do have CRI Extended as well, which is a score given on the evaluation on all 15 colors.
The issue with CRI is it's just looking at how a light performs with 8 colors. A manufacturer can game the system so that it looks good for the 8 colors, but does not accurately reproduce all colors.
Most gaffers and DP's who want to look at how accurately a light will reproduce skin tones will look at the following colors:
Ra - This is the average of R1-R8 R9 - Strong Red R13 - Light Yellowish Pink R15 - Asian Skin
If a light has a high CRI (Ra) value and high R9, R13, R15 values, all above 85, that is a good indicator that it will accurately reproduce skin tones. R9 is out of gamut for some digital cameras, but it is still used as a skin tone value to compare lights.
Other specifics to look at:
R10 - Strong Yellow R11 - Strong Green R12 - Strong Blue R14 - Moderate Olive Green
If the above all renders properly as well, you most likely have a light that won't suffer from strong color rendering issues.
The main issue with CRI is it's easy for a manufacturer to get a high score and still have bad color issues with their fixture.
TLCI
Stands for Television Lighting Consistency Index
Uses a 3 chip broadcast camera as the observer. Looks at the first 18 colors of an X-Rite color checker classic chart. It takes into consideration that R9 is out of gamut of some television cameras and therefore may not be the best to use for comparison.
It's measured from 0-100
Its score is evaluated in two ways.
- In a film style production where you will be color grading later
- In a broadcast-style production where you are streaming live.
TLCI assumes a Rec709 colorspace and that digital cinema cameras have very different spectral sensitivities. As a result, this may give you skewed results that may favor one camera over another.
TLMF
Television Luminaire Matching Factor is a companion metric to TLCI that gives you a score from 0-100 on how two lights compare to one another. This uses all 24 patches on the X-Rite Color checker to compare the two fixtures together.
TM-30
Stands for Technical Memorandum-30. Usually, you will see it with an additional dash and number after it, for example, TM-30-18. This is because it's version 18 of TM-30. Most likely will be the score that replaces CRI because of its increased accuracy and the fact that it is much more difficult to build your light to score high while not rendering colors accurately.
Has two values
Rf - Measures color fidelity on a scale of 0-100. A higher score is better.
Rg - Scaled between 60-140 with a score below 100 being less saturated, a score above 100 being more saturated. Closer to 100 means it is more accurate.
A corresponding graph called the Color Vector Graphic will be displayed to show if any colors may be over or under saturated.
Evaluates 99 colors
SSI
Stands for Spectral Similarity Index.
Looks at the spectral distribution and takes measurements and compares it to a measured source. This can be thought of as a confidence factor. It represents how confident you can be that it will render colors accurately.
You can also pick standard light sources and compare them to that.
90-100 is excellent 80-90 being good 70-80 possible problems 0-70 most likely will have color rendering issues.
If any lights score low its a good indicator that it will be difficult to resolve in post. Can help you find lights that will match.