CRI and bruised skin color rendering

PhotonWrangler

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I had a nasty bruise on the back of my hand recently after accidentally smacking it on something. A day or so later I noticed that it was turning from red to blue-black (normal for bruises). What startled me was how different it looked under the two different LED bulbs in my home office. One of the bulbs makes it look very blue-black, and the other one seems to hide the bruising somewhat.

As the healing process continued and the blue-black areas changed to yellow-green as the hemoglobin broke down, one of the lamps still make my skin look bruised while the other one made it look almost completely healed. As I waved my hand between the two bulbs, the bruise would appear and disappear. It was like a magic trick.

Both of these bulbs are in the 2700k-2900k range. The one that makes it look better is one of the original Philips alien-head lamps (still going strong after several years) while the one that reveals more of the blue-black is a slightly newer Philips "ice cream cone"' bulb. They both produce similar light to my eyes but the CRI is apparently quite different between them, probably the ratio of red to blue wavelengths.

Anyway this seems to point out the importance of CRI for medical examinations. I just didn't realize it made that much of a difference until this happened.
 

KITROBASKIN

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Last school year one of my students who had diabetes would have to get his ketones checked on occasion. The test strip would reveal a certain shade of a brownish color to indicate ketone level. The overhead fluorescent lights in the health room were actually not horrible compared to the Hi CRI Nichia emitter that was on my person.
 

PhotonWrangler

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Last school year one of my students who had diabetes would have to get his ketones checked on occasion. The test strip would reveal a certain shade of a brownish color to indicate ketone level. The overhead fluorescent lights in the health room were actually not horrible compared to the Hi CRI Nichia emitter that was on my person.
Nice. So the result was still a bit more discernible on your Nichia?
 

LEDphile

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Both of these bulbs are in the 2700k-2900k range. The one that makes it look better is one of the original Philips alien-head lamps (still going strong after several years) while the one that reveals more of the blue-black is a slightly newer Philips "ice cream cone"' bulb. They both produce similar light to my eyes but the CRI is apparently quite different between them, probably the ratio of red to blue wavelengths.
There were a couple variants of the old remote-phosphor lamps - was this one of the original dark silver body / yellow head lamps, or one of the slightly newer white body / yellow-green head L-prize lamps?

The original lamp had a CRI around 75 IIRC, while the L-prize lamp had a CRI of 92 (and the newer-style lamps are typically CRI 80 or above)

The overhead fluorescent lights in the health room were actually not horrible compared to the Hi CRI Nichia emitter that was on my person.
The fluorescent lamps in healthcare diagnostic environments are not always the same as you'll find in an office environment, precisely because of how important the color rendering can be for diagnostics. There's a good chance that the exam room was using 90CRI lamps instead of the more typical 80CRI tubes.
 

TPA

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I still remember back when Littlite came out with their first LED lamps, they used white LEDs plus red LEDs to get decent color rendering. I'm kind of surprised this isn't implemented more since it's simple and cheap.
 

PhotonWrangler

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There were a couple variants of the old remote-phosphor lamps - was this one of the original dark silver body / yellow head lamps, or one of the slightly newer white body / yellow-green head L-prize lamps?

The original lamp had a CRI around 75 IIRC, while the L-prize lamp had a CRI of 92 (and the newer-style lamps are typically CRI 80 or above)
The remote phosphor lamp is the original type with the silver body. It's the one that makes people say "That's a light bulb?!" So yes it's the lower CRI version.
 

degarb

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Greeting Photon Wrangler! I am overjoyed that you bruised yourself and found this out, lol🤣. I have been saying this for years. A low cri of the correct color works better than a high cri of a wrong color temperature. The skin is somewhat transparent and different colors bring out different details, layers, etc.

It's kind of like a tuned antenna for the frequency desired and tuning out unwanted frequencies, is more desirable than an untuned antenna.

We white people, prefer lights that emphasize healthy red blood vessels and not our dead skin layer or green or blue veins. Especially our dark circles under our eyes. But in medicine this is not always the goal, nor is this the goal in other color inspection fields or tasks.

I used to have a blue bathroom that the former owner put one coat over peach with a fair number of hidden streaks, ghosts and tiny skips. I used her bad paint jobs to judge my lights. I could walk into the room with a 7 lumen red and all the peach misses would jump out, but they were hidden in normal fixed lighting and hard to find with high intensity white lights. - - Inspection of color (tiny difference) was a big part of my job.

I even went as far as gathering all available paint chips from Lowes, HD, Ace, and the paint store, glued them on a pizza box with each color on top of each other with the least difference in color. I would use this as the way to test different lights, cri, intensity, and Kelvin.

The result of the pizza box test (also had a rainbow spyglass so I could see how lights lacking spectrum worked for discerning color difference) seemed to support more scientific assessment that human color sensitivity is not only influenced by cri, but intensity, gamut Area Index (saturation).

My 4000k metal halides do a very good job beauty and saturation for my color inspection, but in the spectrophotometer you see narrow bands and chunks missing. Nevertheless all colors on the paint charts had subtle discrimination, although they are like 65 cri.

A 70 cri 6500k light renders my baby blue back door more beautifully than my 90 cri 3000k nichia. But the 3000k nichia beats the pants off my 4000k 70 cri on the baby blue backdoor. It all comes down to which colors you wish to see the best! And I say this as a professional color inspector.

This is only one reason why tunable lights are so important. The other reason is mood. We need different moods for different times of the day.
 
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degarb

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😀🤣. I read about 15 years ago that adults appreciated and enthused about LED technology, while kids took it for granted.

I guess it depends on if in your formative years you felt handicapped by the lack of affordable lighting or not....Me, I am not sure because I generally nodded off much of my teens during the winter months from the lack of bright lights during the winter months in North East Ohio,after moving up from bright sunny Florida. That is when I wasn't under bright florescent school lighting, looking rather green in the schools bathroom mirror. It wasn't easy being green.

Now, now I wonder if photon Wrangler still misses the old fashioned flaming Christmas Lights and annual tree conflagrations.
 

PhotonWrangler

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😀🤣. I read about 15 years ago that adults appreciated and enthused about LED technology, while kids took it for granted.

I guess it depends on if in your formative years you felt handicapped by the lack of affordable lighting or not....Me, I am not sure because I generally nodded off much of my teens during the winter months from the lack of bright lights during the winter months in North East Ohio,after moving up from bright sunny Florida. That is when I wasn't under bright florescent school lighting, looking rather green in the schools bathroom mirror. It wasn't easy being green.

Now, now I wonder if photon Wrangler still misses the old fashioned flaming Christmas Lights and annual tree conflagrations.
I DO miss the old flame-style incandescent Christmas lights, the ones that were made of heavy glass with the pigment on the inside of the bulb.
vintage_C9_Christmas_lights.jpg
 

PhotonWrangler

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Greeting Photon Wrangler! I am overjoyed that you bruised yourself and found this out, lol🤣. I have been saying this for years. A low cri of the correct color works better than a high cri of a wrong color temperature. The skin is somewhat transparent and different colors bring out different details, layers, etc.

It's kind of like a tuned antenna for the frequency desired and tuning out unwanted frequencies, is more desirable than an untuned antenna.

We white people, prefer lights that emphasize healthy red blood vessels and not our dead skin layer or green or blue veins. Especially our dark circles under our eyes. But in medicine this is not always the goal, nor is this the goal in other color inspection fields or tasks.

I used to have a blue bathroom that the former owner put one coat over peach with a fair number of hidden streaks, ghosts and tiny skips. I used her bad paint jobs to judge my lights. I could walk into the room with a 7 lumen red and all the peach misses would jump out, but they were hidden in normal fixed lighting and hard to find with high intensity white lights. - - Inspection of color (tiny difference) was a big part of my job.

I even went as far as gathering all available paint chips from Lowes, HD, Ace, and the paint store, glued them on a pizza box with each color on top of each other with the least difference in color. I would use this as the way to test different lights, cri, intensity, and Kelvin.

The result of the pizza box test (also had a rainbow spyglass so I could see how lights lacking spectrum worked for discerning color difference) seemed to support more scientific assessment that human color sensitivity is not only influenced by cri, but intensity, gamut Area Index (saturation).

My 4000k metal halides do a very good job beauty and saturation for my color inspection, but in the spectrophotometer you see narrow bands and chunks missing. Nevertheless all colors on the paint charts had subtle discrimination, although they are like 65 cri.

A 70 cri 6500k light renders my baby blue back door more beautifully than my 90 cri 3000k nichia. But the 3000k nichia beats the pants off my 4000k 70 cri on the baby blue backdoor. It all comes down to which colors you wish to see the best! And I say this as a professional color inspector.

This is only one reason why tunable lights are so important. The other reason is mood. We need different moods for different times of the day.
Hi Degarb! I love the pizza box paint chip tool. I'm imagining making a small version of that on a disk, mounting the disk to a motor, adding a magnetic pickup for tach pulses to monitor the disk's position and a phototransistor to pick up reflectance, then spinning it and using the photodetector's output to graph the spectral response for each chip position. It would look pretty kludgey but I think it would work. :)
 
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