Light Bulb CRI_Grades

I was kinda hoping for some reactions after taking the time to compile that post…

Except for Duv and angular tint shift, both of which are extremely important and noticeable.

Edit to add: I don’t think I’ve ever seen bad tint shift in a household bulb because they’re generally quite diffuse, but it’s common in flashlights. Look at the beam from a flip-chip Cree like XP-G3 or XP-L2 in a reflector and see all the rainbow colors.

Duv is harder for companies to keep under control. Because our vision is so sensitive to green light, adding just a bit of green can bump the lumens way up without wrecking CRI, in order to recapture some of the efficiency penalty you normally find with high-CRI LEDs. But doing this also gives the light a green tone (a positive Duv), which deeply annoys a lot of people.

I don’t want to say CRI_Grade is anything more than a color rendering score… But at these strict of levels, I don’t know of any real life bulbs that would have bad Duv or tint shift while scoring good on CRI_Grade.

Whats the advantage of this over something like CQS or TM-30?

About CRI rendering: recently, I started to appreciate the newest CRI measuring method, which uses two values to present overall CRI. Rf (fidelity) is very similar in meaning to Ra (I won’t try to research for the differences now), and the other value is Rg (gamut), which tells, that how much the examined light source is greenish/yellowish (values under 100) or rosy (values above 100).

Rf measures as the same as Ra (range 0-100).
Rg measures from (100 minus Rg’) to (100 plus Rg’), where Rg’ = 100 - Rf

I would use a starting formula something like this:
0.7 × (Rf / 100) × Rf + 0.7 × ((100 - Rf) / 100) × Rg’’ + 0.15 × R9 + 0.15 × R12

Rg’’ is calculated like this: 100 - (abs(100 - Rg) * (100 / Rg’)) - this tells us, how much the light source deviates from the black body line, if compared with other light sources having the same Rf.

So, for example, if an emitter with Rf=90, has an Rg of 93 (could be called very dull or greenish) or 107 (could be called very ill or rosy), has an Rg’’ score of only 30, while light source spot on BBL would have Rg’’ = 100.

The first two Rf based coefficients corrects for the cases, where e.g. Rf = 98 and Rg = 102 -> that is definitely not a bad light source, which would deserve Rg’’ of 0.

Edit: Please ignore above anything I said related to Rg, as of maukka’s clarification.

Speed and simplicity would be the advantage. Can you imagine if I posted all 41 of the TM-30 (or CQS) diagrams and your job was to spot the best ones? Or sort them?

That route crossed my mind, but where are you going to get all that data? It’s hard enough finding CRI data alone. Plus, Rg and Rf aren’t the same sensitivity as CRI, like you noticed, so fixing that is iffy and untrustworthy imho.

Yes, I know, that this is hard to get, but all light sources, which was tested by maukka, have these data.

Like I say, it’s no replacement for reading a data dump if you can (and have it). But it sure is slick as an alternative grading method.

TM-30 Rg describes how saturated colors seem on average. It’s not directly correlated with duv (magenta/green tint).

Here’s a link to TM30-15 Excel calculator which you can use if you have SPD data from a spectrophotometer.

Oh, good to know. Maybe more good examples would be needed here for my better understanding.

Still, basically, anytime I see an Rg above 100 in a measurement, the duv reading is negative and for Rg under 100, the duv reading is positive. Would be good to know, how indirect the correlation can be.

The inherit limitation as you’ve noted is the CRI Ra being limited the 8 pastel colors being tested. With something like TM-30 including a wider and deeper sample base the Rf means a lot more than CRI Ra.

Here’s a couple examples:
Yuji BC duv –0.0024 Rg 96
Optisolis duv +0.0018 Rg 101

I see. Thank you.

Thanks. I use LibreOffice Calc (instead of MS Excel), and it says it can not open those files because “the maximum number of columns per sheet was exceeded”.

But my meter gives me TM-30, Rf,Rg, SPD picture, all that with each reading, so I think I am covered.

The CRI_Grade system mostly fills my need to rank bulbs I have never tested against the ones I have.

Really though, R9 and R12 can be trusted to break away from the pack first, so even if Ra was including R10,11,13,14,15, it wouldn’t change much.

Actually, it seems opposite to me. By including too many samples that average the same, you dilute the significance of R9 and R12, where the real differences are.

Having used a few bulbs that were below the BBL, I’m really not a fan for home/area lighting, if there’s any sunlight or other light sources it makes them look strange and artificial, and they make all other light sources look super green in comparison (even my calibrated computer monitor) which defeats the purpose IMO.

Low-CRI and -duv would be even worse, they look like fluorescents and I’d deal with swapping incandescent bulbs before going back to that, same reason I stick with high-CRI in my flashlights. The lack of much of the spectrum is immediately apparent to me personally.

Reminder that sunlight, fires, etc. (all the light sources we have evolved to be used to) are on or above the BBL. Rosy tint shouldn’t be taken as objectively desirable for all environments, that’s why Nichia for example offers specific tints and spectrum profiles for different types of retail, groceries, etc.

Sunlight is usually a lot higher CCT than any bulbs you can buy. What CCT are you using?
And I’m with you on not being impressed by rosy tints.

Also, on a super interesting note, I have the backlights from 2 PC monitors in that table! “DELL” is my PC, and “HP ENVY” is my wife’s. I opened Notepad to make a white screen, them measured with the meter against the screen.