CRI

[ptonsparky]

What would be considered a high CRI? Retail sales.
How do I know that it actually is what the mfg states? Trust?

 

[bzzt]

90+

That’s usually what is specd on state, federal design

Some manufacturers are big fat liars (ie, anything sold on Amazon)


Sent from my iPhone using Tapatalk

 

[Flicker Index]

Some performance cars have the gear ratios tuned so the top end of 1st gear (like Viper) or 2nd gear falls right at 60 mph to score well on the 0-60 test. A car with transmission set where the shift point lands at 70 mph would do better on the 0-70 test, but worse on 0-60. These differences may or may not be meaningful in real life. CRI differences within a reasonable range are just like that. It's an indication of how accurately standard color swatches are rendered.

CRI values have no meaningful purpose beyond how those samples swatches are rendered. In real world, there are many objects that exhibit selective absorption and fluorescence and what we see is a combination of all the effects. For examples, certain plastics and tonic water exhibits very slight purplish blue tinge under natural light but LEDs are incapable of producing these effects due to their lack of emissions shorter than blue, so paper and fabric brighteners that make things look vibrant under sunlight, incandescent or GSFL can look dinghy under artificial LED lighting even if you're comparing LED whose CRI is 92 against a CFL with CRI of 80. Fitness for retail sale presentation really depends on what you're selling.


I think we can all recall those times when you're watching a YouTube video and you can see the person's skin slowly fading back and forth between greenish and pinking every several tens of seconds. This phenomena has become more common with the proliferation of LED lamp which often returns the flicker level to something comparable or worse than magnetic ballast fluorescent lighting due. This effect is more intensified at higher illumination level when the shutter speed/integration time is less than several complete half cycles.

LEDs are considered low/near zero persistence lighting elements and getting a completely steady requires regulated DC supply and many LED ballasts are not up to par and they often have more light flicker than mid 20th century magnetically ballasted fluorescent technology. (FL lamps are considered high persistence devices). Since power is delivered twice per cycle and lights glow on both polarities, the flicker frequency is 120Hz.

CRI of white light generally only affects the presentation to naked eyes. Cameras can adjust gains on color channels and correct it as if we were to wear tinted glasses, but in these remote commuting days, compatibility with video devices is more important than ever before. The flicker depth has to be low enough even at high frequency in order to remain compatible with both the interlace frequency to avoid "banding" (interlacing
Since your videography device sampling rate/shutter is not phase locked to line frequency, the part of line cycle the lamp is on when the video frame is captured slowly slides around.

As more people work in remote environment, how things look televised is more important than ever before. The attached photo is an example of interaction between electronic rolling shutter and flicker that is carried through into light due to hard switching PWM based dimming employed by the particular LED Ballast.

 

[bzzt]

Some performance cars have the gear ratios tuned so the top end of 1st gear (like Viper) or 2nd gear falls right at 60 mph to score well on the 0-60 test. A car with transmission set where the shift point lands at 70 mph would do better on the 0-70 test, but worse on 0-60. These differences may or may not be meaningful in real life. CRI differences within a reasonable range are just like that. It's an indication of how accurately standard color swatches are rendered.

CRI values have no meaningful purpose beyond how those samples swatches are rendered. In real world, there are many objects that exhibit selective absorption and fluorescence and what we see is a combination of all the effects. For examples, certain plastics and tonic water exhibits very slight purplish blue tinge under natural light but LEDs are incapable of producing these effects due to their lack of emissions shorter than blue, so paper and fabric brighteners that make things look vibrant under sunlight, incandescent or GSFL can look dinghy under artificial LED lighting even if you're comparing LED whose CRI is 92 against a CFL with CRI of 80. Fitness for retail sale presentation really depends on what you're selling.


I think we can all recall those times when you're watching a YouTube video and you can see the person's skin slowly fading back and forth between greenish and pinking every several tens of seconds. This phenomena has become more common with the proliferation of LED lamp which often returns the flicker level to something comparable or worse than magnetic ballast fluorescent lighting due. This effect is more intensified at higher illumination level when the shutter speed/integration time is less than several complete half cycles.

LEDs are considered low/near zero persistence lighting elements and getting a completely steady requires regulated DC supply and many LED ballasts are not up to par and they often have more light flicker than mid 20th century magnetically ballasted fluorescent technology. (FL lamps are considered high persistence devices). Since power is delivered twice per cycle and lights glow on both polarities, the flicker frequency is 120Hz.

CRI of white light generally only affects the presentation to naked eyes. Cameras can adjust gains on color channels and correct it as if we were to wear tinted glasses, but in these remote commuting days, compatibility with video devices is more important than ever before. The flicker depth has to be low enough even at high frequency in order to remain compatible with both the interlace frequency to avoid "banding" (interlacing
Since your videography device sampling rate/shutter is not phase locked to line frequency, the part of line cycle the lamp is on when the video frame is captured slowly slides around.

As more people work in remote environment, how things look televised is more important than ever before. The attached photo is an example of interaction between electronic rolling shutter and flicker that is carried through into light due to hard switching PWM based dimming employed by the particular LED Ballast.

So what is a normally acceptable CRI? Doesn't CRI tend to degrade over time?
Manufacturers I've used are the typical- sylvania, GE, phillips,

 

[James L]

A high CRI would be 100, the highest. That's what you get with incandescent and halogen. When you're talkin about retail, you're always wanting to be as close to that as possible. 95+ if you can

I would think 92 or 93 at a minimum

 

[gadfly56]

A high CRI would be 100, the highest. That's what you get with incandescent and halogen. When you're talkin about retail, you're always wanting to be as close to that as possible. 95+ if you can

I would think 92 or 93 at a minimum

Are you sure about that? I thought the reference was sunlight. Incandescent would be way warmer, about 2300K vs 5000K.

 

[James L]

Are you sure about that? I thought the reference was sunlight. Incandescent would be way warmer, about 2300K vs 5000K.

100% positive about that.
Sunlight is 100 CRI
incandescent light is 100 CRI
Halogen light is 100 CRI

 

[James L]

Here...

 

[gadfly56]

Here...

OK, I see what the screen shots show, but they definitely don't make sense (to me). If you look at the spectrum of each source, they are WAY different.

 

[James L]

OK, I see what the screen shots show, but they definitely don't make sense (to me). If you look at the spectrum of each source, they are WAY different.

CRI doesn't relate to the color of the light output, it relates the how true something looks with light cast on it.

In other words, the color of fruits and vegetables. The color of clothing. The color of furniture, etc.

Does the light render a correct color on the items.

That's why fluorescent tubes can have the same CRI regardless of the color
735 is 70 CRI at 3500k
741 is 70 CRI at 4100k

835 is 80 CRI at 3500k
841 is 80 CRI at 4100k

The color of the light coming out of the bulb or tube doesn't determine CRI

 

[gadfly56]

CRI doesn't relate to the color of the light output, it relates the how true something looks with light cast on it.

In other words, the color of fruits and vegetables. The color of clothing. The color of furniture, etc.

Does the light render a correct color on the items.

That's why fluorescent tubes can have the same CRI regardless of the color
735 is 70 CRI at 3500k
741 is 70 CRI at 4100k

835 is 80 CRI at 3500k
841 is 80 CRI at 4100k

The color of the light coming out of the bulb or tube doesn't determine CRI

OK, I think I see what you're saying. So the claim is that sources with the same CRI will render colors that appear the same relative to each other regardless of color temperature? I did stage lighting design in community theaters for 20 years. I'm not sure I'm buying what they're selling.

 

[wwhitney]

CRI is computed by comparing a light source to a reference light source of the same corrected color temperature (a blackbody radiator for color temperatures < 5000K). The comparison is using just eight standard color samples, and for each sample the reflected light from the subject light source is compared to the reflected light from the reference light source.

One of the criticisms of CRI is that the 8 standard colors underweight the importance of the red end of the light source spectrum. Accordingly California's performance standard JA8 for LED lamps requires both a CRI of 90 or more, and an R9 score of 50 or more. R9 is the test using a saturated red sample.

Color rendering index - Wikipedia

en.wikipedia.org

Cheers, Wayne

 

[gadfly56]

CRI is computed by comparing a light source to a reference light source of the same corrected color temperature (a blackbody radiator for color temperatures < 5000K). The comparison is using just eight standard color samples, and for each sample the reflected light from the subject light source is compared to the reflected light from the reference light source.

One of the criticisms of CRI is that the 8 standard colors underweight the importance of the red end of the light source spectrum. Accordingly California's performance standard JA8 for LED lamps requires both a CRI of 90 or more, and an R9 score of 50 or more. R9 is the test using a saturated red sample.

Color rendering index - Wikipedia

en.wikipedia.org

Cheers, Wayne

I see from the Wiki article you linked to that there are a number of apparent/alleged defects in the CRI methodology. So, pretty complex and still an evolving thing.

 

[Flicker Index]

A high CRI would be 100, the highest. That's what you get with incandescent and halogen. When you're talkin about retail, you're always wanting to be as close to that as possible. 95+ if you can

I would think 92 or 93 at a minimum

Incorrect. It depends on what you're trying to accomplish. Broad spectrum lamps like Chroma 50 are used to try to standardize things in printing industry and collision repair so the presentation of color is consistent from one location to another. You could have something that contains the inaccuracy by the same amount, but one could be flattening it while the other could be overemphasizing it.

So, a 5000K 91 CRI L.E.D. won't be the same, or "better" than the 90 CRI General Electric F40T12/C50.
Read https://designinglight.com/?p=954

Retailing lamps like Promolux ( https://a89b8e4143ca50438f09-7c1706...iginal/promolux-14032-bulletin.pdf?1440191211 ) and the GE Reveal color distorting lamps contain calculated distortion in favor of what's believed to be "pleasant" appearance. these lamps are designed to purposely introduce distortion. Some visual enhancement lamps have CRI in the 60s, yet they produce "desirable" presentation.

 

[Sparky1981]

Just as an FYI most lighting designers now are moving away from CRI in favor of TM-30 Using TM-30 to Improve Your Lighting Design – Illuminating Engineering Society (ies.org)

 

[ptonsparky]

I noticed there were other methods.

High CRI fixtures for the office were 10 weeks out. The owner decide the help would never know the difference if he didn't tell them.

 

[winnie]

The only way to really know what is going on is to compare the spectrum of the light sources.

Things like CRI or color temperature are single value descriptions of the complete spectrum. Like rms voltage or crest factor describe ac waveforms but you need an oscilloscope to see the details that rms hides away.

Jon

 

[James L]

The only way to really know what is going on is to compare the spectrum of the light sources.

Things like CRI or color temperature are single value descriptions of the complete spectrum. Like rms voltage or crest factor describe ac waveforms but you need an oscilloscope to see the details that rms hides away.

Jon

Yes, like the spectrum of a speaker. It plays every hz within a range, but some better than other. And there's a resonating frequency. Not exactly the same, but it works for me

Some lights have missing places in the spectrum, and that has an effect.

A black body, like the sun, incandescent, halogen, are what to strive for. Here's a few images that might help.

BTW, red is REALLY hard to get a good CRI in LED