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Chanon Wangtrirat

ALQI - The sum of CRI (Ra+R9+R12+R15) + SSI + TLCI

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Posted (edited)

Hi! I'm Thomas. 

After I used CRI to measure such thing so long ago with those flos now LEDs. 

I found these measurement of SSI, TLCI, TM-30 too complicated to evaluate light when you just want to buy one, It's too much data use to judge how good light is.

True that SSI has been invented but we are too far from getting such technology like LED to get perfect score or even touch 85 in daylight without using UV chip instead of blue. Which mak SSI score look awkward especially when compare to conventional lightsource like HMI or tungsten. 

BTW SSI invented to use to match 2 lightsources not directly use to evaluated such light quality. It could be use but honestly look awkward to me.

So I came up with something more simple of single number defined quality of light 

ALQI = Average Light Quality Index 
Simply calculated from 
- CRI : Ra, R9(red), R12(blue), R15(skintone)
- SSI : measured with CIE CCT closest to lightsource you measure IE. 5600K (input color temperature on Sekonic C800)
- TLCI Representing camera sensor.
 
Just average 6 measurements and you will come up with ALQI 
 
100 = Perfect
< 70 : Severe Color shift
< 80 : Some Color shift
> 80 : Usable for most photographic task
> 85 : Great for most photographic task
> 90 : Excellent for most photographic task
> 95 : Reference class match
 
Here's some ALQI various sources from my own measurements and internet
 
Direct Sunlight (Thailand) 9.40AM 5600K        ALQI = 99.3
KinoFlo KF55 20W Fluorescent                          ALQI = 83.1
Incandescent 2700K                                            ALQI = 99.3
5000K LED CRI98+                                               ALQI = 91.4
3000K CRI98 LED Chip                                        ALQI = 93.4
Sylvania 3w 2700K generic household.            ALQI = 65.5
MasterPor 5000K Light                                       ALQI = 87.9
1W 3030 CRI98 LED Chip 6000K                       ALQI = 90.5
Nanlite Forza 60B 3200K                                    ALQI = 87
Nanlite Forza 60B 5600K                                    ALQI = 89.2
Nanlite Forza 200 5600K                                     ALQI = 90.6
Fuji XT-20 Xenon Flash                                        ALQI = 95.4
Luminus COB 300W 5600K                                 ALQI = 88.5
Luminus COB 150W 3200KK                              ALQI = 87.1
Litepanel Gemini 1x1 5600K                               ALQI = 87.1
Litepanel Gemini 1x1 3200K                               ALQI = 88.3
Rayzr MC 400 MAX 3200K                                  ALQI = 72.3      
Rayzr MC 400 MAX 5600K                                  ALQI = 86.8
Aputure NOVA P300c 3200K                              ALQI = 91.9
Aputure NOVA P300c 5600K                              ALQI = 92.2
 
 
If you have C-800 in your hand you can help me fill the table of such lightsources. 
Happy rigging!!!!
Thomas
                             
 
Edited by Chanon Wangtrirat

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Lupo Superpanel Dual Color 60 5600K ALQI = 87
Lupo Superpanel Dual Color 60 3200K ALQI = 89.4
LEDGO Altatube 5600K ALQI = 86.8
LEDGO Altatube 3200K ALQI = 90.5
Luxli Taiko 5600K ALQI = 90
Luxli Taiko 3200K ALQI = 94.3
ROTOLIGHT TITANX2 5600K ALQI = 87.7
ROTOLIGHT TITANX2 3200K ALQI = 90.4

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Hmm, I could measure some of the stuff I have here.

But I think in the end we can keep coming up with different numbers forever. It is hard for something to have a good TLCI, but be really bad at R9 or R12.

P

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31 minutes ago, Phil Rhodes said:

Hmm, I could measure some of the stuff I have here.

But I think in the end we can keep coming up with different numbers forever. It is hard for something to have a good TLCI, but be really bad at R9 or R12.

P

I find it easy to differentiate such product apart from "97 TLCI" "97CRI" some of them get these numbers but end up in 80~ range ALQI

Surprisingly Aputure P300C got best here on daylight.

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Why not just use the TM30-18 Rf scores? With 100 color samples and a very intuitive graphic showing color gamut as well as shift, I think it's pretty hard to beat. It is based on the standard human observer, much like CRI, which can be an issue, but it certainly gives us more information with more data points and is thus harder to cheat. As far as I know, TLCI is based on CCD sensors, so it might not be an accurate predictor of CMOS sensor characteristics. SSI is the only one of the three with a real advantage, being that one can easily change the reference source if they want to match non-Planckian sources like gelled lights or fluorescents.

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I think all of these numbers can only be so helpful. Every camera is different - Everyone talks about how bad skypanels are, but they look really great on the alexa. 

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You're going to get accumulated error by averaging all the scores--which each have their own margin of error--into a single score. The error of one value on it's own is not that big a deal, but you could potentially get a misleading value when they're all factored together. Unless you are ensuring your instruments are calibrated and accurate, this will be a problem.

What is the issue with SSI? It's just that the numbers aren't high enough for LEDS? That's kind of the point, the numbers aren't supposed to favor any one light source--they're just supposed to tell it like it is.

Regardless, I think any single number value will ever tell the full story. Simply look at the spectrum overlaid on top of daylight, and you'll immediately be able to evaluate how the light will perform.

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13 hours ago, Albion Hockney said:

I think all of these numbers can only be so helpful. Every camera is different - Everyone talks about how bad skypanels are, but they look really great on the alexa. 

Yeah that’s exactly why I average this and called “average light quality index” as if you use solely SSI to evaluate it that will render skypanel crappy.

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Skypanel is not that great.

It was presumably engineered to suit Alexa, given the corporate situation surrounding it.

The colour is only one issue; they're also amazingly heavy, a bit flimsy and incredibly expensive.

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3 hours ago, Phil Rhodes said:

Skypanel is not that great.

It was presumably engineered to suit Alexa, given the corporate situation surrounding it.

The colour is only one issue; they're also amazingly heavy, a bit flimsy and incredibly expensive.

It introduced at the time that LED was not that mature, mediocre efficiency and less predictable color back then. I don’t surprise why Arri choose that route back then. It’s more predictable than most light there plus get function like changing color. So yeah it tuned toward alexa. 
it’s  overdue for arri to come up with something better than skypanel(form) fixture.

fact is Mike Wagner who do marketing for ARRI lighting moved to Litegear as CEO.

Also my DIY panel already copy form of litemat for my usage because it’s so lightweight.

BTW, i cant find SSI of skypanel. Could someone measured that?

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On 8/8/2020 at 6:12 AM, Chanon Wangtrirat said:

It introduced at the time that LED was not that mature, mediocre efficiency and less predictable color back then. I don’t surprise why Arri choose that route back then. It’s more predictable than most light there plus get function like changing color. So yeah it tuned toward alexa. 
it’s  overdue for arri to come up with something better than skypanel(form) fixture.

fact is Mike Wagner who do marketing for ARRI lighting moved to Litegear as CEO.

Also my DIY panel already copy form of litemat for my usage because it’s so lightweight.

BTW, i cant find SSI of skypanel. Could someone measured that?

If you want a value that measures how lights look through a camera specifically, that's what TLCI is for.

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2 hours ago, Andy Jarosz said:

If you want a value that measures how lights look through a camera specifically, that's what TLCI is for.

To be a real pedant, TLCI is predicated quite specifically on a broadcast TV workflow. However, I think it's unlikely that any light which scores well on TLCI is likely to be unpredictable in any common use case, unless there's something really unusual involved. 

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All I'm saying is Quasar Bulbs for example have a high TLCI, but they always look a little magenta. Skypanels in tungsten match damn near perfect to tungsten lights on camera. I know you hate skypanels and I agree they are overpriced, they are too heavy, and the numbers don't look that great - but like all arri products they work. 

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4 hours ago, Albion Hockney said:

All I'm saying is Quasar Bulbs for example have a high TLCI, but they always look a little magenta. Skypanels in tungsten match damn near perfect to tungsten lights on camera. I know you hate skypanels and I agree they are overpriced, they are too heavy, and the numbers don't look that great - but like all arri products they work. 

I should have mentioned this in my other post, but TLCI is not the best metric to evaluate lights on. Like CRI, it can be "gamed" through particular tuning of the light. SSI is my preference.

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The thing with SSI, and all the TM-x stuff, is that it defines similarity to some ideal. Yes, that's more or less what all of them have to do inasmuch as they're targeting cameras which are targeting our eyes which are targeting sunlight. Still, I suspect that people will always want a quality number that isn't relative to a variable. People like CRI because high numbers are good, and interpreting an SSI requires a lot more interpretation, understanding, and frankly subject area expertise.

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1 hour ago, Phil Rhodes said:

The thing with SSI, and all the TM-x stuff, is that it defines similarity to some ideal. Yes, that's more or less what all of them have to do inasmuch as they're targeting cameras which are targeting our eyes which are targeting sunlight. Still, I suspect that people will always want a quality number that isn't relative to a variable. People like CRI because high numbers are good, and interpreting an SSI requires a lot more interpretation, understanding, and frankly subject area expertise.

I would say that is the only way to truly empirically evaluate a light source. I don't want a "colored" number or one that is tailored for any specific capture device, be it a camera or a human eye.

When I hear the Skypanels have low color rendering scores but look great on Alexa cameras, I don't go "what's wrong with the light?" I go "What's wrong with the camera?" As a creative, you want a light to be as unbiased as possible so that your big choices--camera and lens--are consistent and predictable across every shooting scenario. A light that only looks good on one kind of camera is not that, and so the color rendering numbers are suitably low.

If look is important to you, it's in your best interest to want to control the variables as much as possible. Only empirical measurements give you enough information to form these decisions.

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Combining totally different metrics into an average seems like an intrinsically flawed methodology to me. As each of the measurements is looking at different things (so the relationships between each measurement aren't 1:1).

CRI is a common reference, but it uses far too limited a sample size to be of much use. At best it's a coarse measurement and has to be treated as such.

TLCI has a number of detractors (on the basis that it was initially measured using primarily broadcast cameras), however, to-date I've found it the most useful and reliable measurement of the bunch - anything in the 90s (and particularly 95+) seems to work very solidly on single-chip cameras, and never requires any target correction in grading.

SSI I like because it's no nonsense, and simply gives you an exact comparison to a "perfect" black-body radiating reference (tungsten or daylight). And when you overlay the spectral readouts of a particular illuminant over a reference spectrum, you can see instantly the colours in which that particular illuminant is going to be deficient.



 

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17 hours ago, Albion Hockney said:

All I'm saying is Quasar Bulbs for example have a high TLCI, but they always look a little magenta. Skypanels in tungsten match damn near perfect to tungsten lights on camera. I know you hate skypanels and I agree they are overpriced, they are too heavy, and the numbers don't look that great - but like all arri products they work. 

That’s what I encountered too. 

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11 hours ago, Phil Rhodes said:

The thing with SSI, and all the TM-x stuff, is that it defines similarity to some ideal. Yes, that's more or less what all of them have to do inasmuch as they're targeting cameras which are targeting our eyes which are targeting sunlight. Still, I suspect that people will always want a quality number that isn't relative to a variable. People like CRI because high numbers are good, and interpreting an SSI requires a lot more interpretation, understanding, and frankly subject area expertise.

You get my point ^^

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6 hours ago, Chanon Wangtrirat said:

You get my point ^^

What Mark and I are trying to say is that by trying to boil the spectrum of a light down to one number, you're always going to be fundamentally lacking critical information. Averaging these values together just gets you an even less specific, less informative number. If you're a professional, you really shouldn't be looking for shortcuts like that--you should want to know the exact performance of the tools you use so you can make informed decisions about how to use them.

For instance, if you know the camera you're using is biased more towards magenta, than choosing a light that has a a higher spectral content in the green part of the spectrum will result in a more neutral image. That is not a decision you can make based on singular numbers--including SSI, though that is the one that will get you closest.

Think about cameras, different cameras absolutely are more sensitive to different colors than others. That's a part of their "color science." So why is there no singular CRI or TLCI type number for cameras? Because cinematographers test them thoroughly, shooting charts and test subjects under different conditions in order to understand how the camera performs. When the time is taken to do things properly, the shorthand numbers become increasingly useless.

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