How do you correcyly measure light temperature?

UnknownSource said:

I am trying to learn if my LED strip I ordered is wrong color or not. I ordered 2700k color bright LED but but visually it looks like 3100k. I am trying to figure out if it just looks like that (3100k instead of 2700k) because I am too close to it or if I actually got wrong color. And when I use android light meter app it also tells me 3100k. I ask because I am wondering if distance affects the color temperature? Like does it come warmer as distance increases or should it stay the same? What is photography standard for checking lightsources? Is there some standard like 1 meter distance from source or any other standard?

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There are devices for that. A bit expensive for what you want. But hey, it is not my money.

https://www.bhphotovideo.com/c/buy/Color_Temperature_Meter/Ntt/Color+Temperature+Meter/N/0

UnknownSource said:

I am trying to learn if my LED strip I ordered is wrong color or not. I ordered 2700k color bright LED but but visually it looks like 3100k. I am trying to figure out if it just looks like that (3100k instead of 2700k) because I am too close to it or if I actually got wrong color. And when I use android light meter app it also tells me 3100k. I ask because I am wondering if distance affects the color temperature? Like does it come warmer as distance increases or should it stay the same? What is photography standard for checking lightsources? Is there some standard like 1 meter distance from source or any other standard?

Click to expand...

There is only one way to measure degrees kelvin accurately.


However, I don't know how important it would be to know as most of us color correct until what we see pleases us. Get ten people working independently on the same photo and you'll have ten different "pleasing" color corrections.

I'm sure there are certain scientific experiments where knowing the color temperature is important; but, seeing what is usually done in post, I don't think photography is one of them.

UnknownSource said:

I am trying to learn if my LED strip I ordered is wrong color or not. I ordered 2700k color bright LED but but visually it looks like 3100k. I am trying to figure out if it just looks like that (3100k instead of 2700k) because I am too close to it or if I actually got wrong color. And when I use android light meter app it also tells me 3100k. I ask because I am wondering if distance affects the color temperature? Like does it come warmer as distance increases or should it stay the same? What is photography standard for checking lightsources? Is there some standard like 1 meter distance from source or any other standard?

Click to expand...

I have no idea how accurate the Android light meter app is, but my wild-ass guess is that it would be just as good as anything on your camera. Commercial lighting professionals, like those who design and install retail store lighting, use a dedicated colour meter. I would guess that very few photographers do, as they would find the white-balancing capabilities of their camera and development software "good enough". They are more likely to use a white card than a light colour meter.

Distance should not have any effect on the colour temperature of a light source. However, if there are multiple light sources, distance from one relative to others may affect the reading.

Are you testing the colour temperature of the light source in an otherwise completely dark room? If not, any other light sources (such as a window during daylight hours) will affect the reading. If you were to measure the colour temperature of light in a room lit by both daylight and a 2700K lamp, I'd expect the measured colour temperature to be greater than 2700K.

UnknownSource said:

I am trying to learn if my LED strip I ordered is wrong color or not. I ordered 2700k color bright LED but but visually it looks like 3100k.

Click to expand...

"Color temperature " strictly speaking, is a property of a back body radiator: these have the property of giving off light that has specific colors at different temperatures, which are described by Planck's Law. While a candle flame, incandescent lamps, the sun and the blue sky all approximate the colors of a black body radiator, LED lights, lasers, fluorescent and other gas-discharge lamps, do not.

To better describe the color of these non-black body lamps, you not only need color temperature, but you also need a tint measurement. For example, here is both a Color temperature and Tint measurement used in adjusting white balance in Adobe Camera Raw:



Color temperature describes a color cast that varies between yellow and blue, while Tint varies between green and magenta. Combinations of both of these gives you the full range of colors.

What the LED lamp manufacturers give you is the "correlated" color temperature or CCT. It excludes the tint value, and only includes the closest color temperature. As any two lamps of the same correlated color temperature may very well have different tints, it is not surprising that they will appear different. Also, there is more than one way of determining the "correlated" part as well, and your two lamps may very well use different methods. There also may be variation between batches of lamps. Finally, it takes good lab practice to make accurate measurements, and in this use case there is hardly much of a good reason to do so: if you don't like a lamp, just return it to the store and get a new one.

So why don't they also give a tint value? Well that isn't the whole story either: a fuller description of the light quality needs to include a full spectral breakdown of the frequencies emitted and how much of each, and such spectral qualities are important in photography. But if color quality is truly important to you, then why are you buying cheap light bulbs? Rather, use those light sources that are known to be photographically good.

UnknownSource said:

I am trying to figure out if it just looks like that (3100k instead of 2700k) because I am too close to it or if I actually got wrong color. And when I use android light meter app it also tells me 3100k.

Click to expand...

Android light meters won't give you accurate measurements, and neither will the measurements given in Adobe Camera Raw, as illustrated above. You need a colorimeter to give you more accurate results: but do you really need more accurate results?

But as mentioned, a colorimeter won't tell you the full story either, and so you need an optical spectrometer or spectrophotometer, along with excellent lab technique to fully characterize light sources. These are expensive and difficult to use.

UnknownSource said:

ask because I am wondering if distance affects the color temperature? Like does it come warmer as distance increases or should it stay the same?

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No it does not change. However, poor lab technique can change the results. Suppose the lamp is not the only light source in the room, or if the wall paint isn't strictly neutral. Also, unless you use a good instrument, you won't get great results anyway.

UnknownSource said:

What is photography standard for checking lightsources? Is there some standard like 1 meter distance from source or any other standard?

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The International Organization for Standardization (ISO) has numerous standards that relate to these kinds of measurements, as well as a vast array of other unrelated standards. Be aware that following these standards requires lots of time, talent, and money, and these standards are intended for top organizations, not individuals doing casual investigations.

ISO doesn't cover everything, however, so you may want to investigate specific products: https://www.xrite.com.

--
http://therefractedlight.blogspot.com

Here are some concrete suggestions for using light well in photography:

• Do a manual white balance by using a neutral colored object as the target.
• Don't use the Kelvin white balance setting based on the color temperature marked on the lamp package. This setting does not include a Tint value nor does it account for inaccuracies in the color temperature value.
• Use all of the same kinds of lamps, and exclude other light sources from your scene.
• Use a high-quality light sources known to have a flat spectrum: this includes direct sunlight, skylight and incandescent bulbs, as well as flashes for the most part.
• Avoid LED, fluorescent, and other gas discharge lamps unless they are known to be good photographically. You way want to calibrate your camera when using these light sources, but this is an extra expense and is error-prone.
• Color Rendering Index or CRI is a poor measure of color quality, and it is specifically designed for human vision, and not photography.

UnknownSource said:

I am trying to learn if my LED strip I ordered is wrong color or not. I ordered 2700k color bright LED but but visually it looks like 3100k. I am trying to figure out if it just looks like that (3100k instead of 2700k) because I am too close to it or if I actually got wrong color. And when I use android light meter app it also tells me 3100k. I ask because I am wondering if distance affects the color temperature? Like does it come warmer as distance increases or should it stay the same? What is photography standard for checking lightsources? Is there some standard like 1 meter distance from source or any other standard?

Click to expand...

Provided there are no other light sources contributing to what the sensor see's, if both your eyes & an android app both place it as 3100K then the chances are they sent you the wrong one.

There's not a huge difference in colour between 2700K & 3100K but a camera should have no difficulty measuring it. I wouldn't be able to judge myself without a known reference of one of those lights to compare it against.

UnknownSource said:

I am trying to learn if my LED strip I ordered is wrong color or not. I ordered 2700k color bright LED but but visually it looks like 3100k. I am trying to figure out if it just looks like that (3100k instead of 2700k) because I am too close to it or if I actually got wrong color. And when I use android light meter app it also tells me 3100k. I ask because I am wondering if distance affects the color temperature? Like does it come warmer as distance increases or should it stay the same? What is photography standard for checking lightsources? Is there some standard like 1 meter distance from source or any other standard?

Click to expand...

I did something similar when my city replaced our high-pressure sodium street lights with LED street lights from General Electric (3000°K CCT rating, cat # ERL1004B330AGRAYLX131).Initially, the neighborhood was in an uproar over the "cold" & "blue" street lights. The commotion died down after a couple months as people got used to our new tungsten-like color. :-D

I wanted to confirm the CCT color rating so I took this RAW photo ~90 minutes before dawn. As usual, my camera's WB was fixed at Daylight. It was also a little foggy so there was a nice haze around each light. As expected, the photo had a nice warm glow:


My new LED streetlights. Far, far, down the street you can see the glow of some HPS street lights that haven't been changed yet for some reason.

I used the white balance tool in ACR and clicked on various items in the photo that "should be" white (especially the glow/haze around each light). I got the following range of color temperature: 2900-3000K, 7-12Magenta. I also confirmed by using my standard 18% gray card, my camera's custom white balance, while standing directly under a light, and got 2900K (I forget the G/M correction number). Depending who you believe (Adobe, Sony, GE), all the numbers were good enough accuracy for me.

So I'd say using your camera custom white balance and/or software white balance corrections should be accurate enough to at least raise a complaint with your LED light manufacturer. If you're just adjusting things by eye on an uncalibrated monitor, your weird color temperature numbers wouldn't surprise anyone here.

--
Lance H

lehill said:

Initially, the neighborhood was in an uproar over the "cold" & "blue" street lights.

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The color temperature which looks “white” gets lower as the illumination level gets lower, or rather, the range of acceptable neutral color temperatures gets rather narrow and restricted at low intensity levels.

So 3000K might look yellow if the lighting is bright, but might look blue if the lighting is dim:

https://en.wikipedia.org/wiki/Kruithof_curve

Please note that the actual relationship has been disputed or is uncertain.

--
http://therefractedlight.blogspot.com

UnknownSource said:

I am trying to learn if my LED strip I ordered is wrong color or not. I ordered 2700k color bright LED but but visually it looks like 3100k. I am trying to figure out if it just looks like that (3100k instead of 2700k) because I am too close to it or if I actually got wrong color. And when I use android light meter app it also tells me 3100k. I ask because I am wondering if distance affects the color temperature? Like does it come warmer as distance increases or should it stay the same? What is photography standard for checking lightsources? Is there some standard like 1 meter distance from source or any other standard?

Click to expand...

Depending on the camera you have available if you take a raw picture with auto white balance set and open it with something like Adobe Camera Raw (ACR) you'll get a reasonable approximation (using As Shot). I would think certainly good enough to make this distinction.

Mark Scott Abeln said:

Here are some concrete suggestions for using light well in photography:

• Do a manual white balance by using a neutral colored object as the target.
• Don't use the Kelvin white balance setting based on the color temperature marked on the lamp package. This setting does not include a Tint value nor does it account for inaccuracies in the color temperature value.
• Use all of the same kinds of lamps, and exclude other light sources from your scene.
• Use a high-quality light sources known to have a flat spectrum: this includes direct sunlight, skylight and incandescent bulbs, as well as flashes for the most part.
• Avoid LED, fluorescent, and other gas discharge lamps unless they are known to be good photographically. You way want to calibrate your camera when using these light sources, but this is an extra expense and is error-prone.
• Color Rendering Index or CRI is a poor measure of color quality, and it is specifically designed for human vision, and not photography.

Click to expand...

Thanks.

If CRI is bad measure for quality, is there any other specs that would tell if that given LED is good for photography?

lehill said:

UnknownSource said:

I am trying to learn if my LED strip I ordered is wrong color or not. I ordered 2700k color bright LED but but visually it looks like 3100k. I am trying to figure out if it just looks like that (3100k instead of 2700k) because I am too close to it or if I actually got wrong color. And when I use android light meter app it also tells me 3100k. I ask because I am wondering if distance affects the color temperature? Like does it come warmer as distance increases or should it stay the same? What is photography standard for checking lightsources? Is there some standard like 1 meter distance from source or any other standard?

Click to expand...

I did something similar when my city replaced our high-pressure sodium street lights with LED street lights from General Electric (3000°K CCT rating, cat # ERL1004B330AGRAYLX131).Initially, the neighborhood was in an uproar over the "cold" & "blue" street lights. The commotion died down after a couple months as people got used to our new tungsten-like color. :-D

I wanted to confirm the CCT color rating so I took this RAW photo ~90 minutes before dawn. As usual, my camera's WB was fixed at Daylight. It was also a little foggy so there was a nice haze around each light. As expected, the photo had a nice warm glow:


My new LED streetlights. Far, far, down the street you can see the glow of some HPS street lights that haven't been changed yet for some reason.

I used the white balance tool in ACR and clicked on various items in the photo that "should be" white (especially the glow/haze around each light). I got the following range of color temperature: 2900-3000K, 7-12Magenta. I also confirmed by using my standard 18% gray card, my camera's custom white balance, while standing directly under a light, and got 2900K (I forget the G/M correction number). Depending who you believe (Adobe, Sony, GE), all the numbers were good enough accuracy for me.

So I'd say using your camera custom white balance and/or software white balance corrections should be accurate enough to at least raise a complaint with your LED light manufacturer. If you're just adjusting things by eye on an uncalibrated monitor, your weird color temperature numbers wouldn't surprise anyone here.

Click to expand...

ACR is Adobe Camera Raw? And how to exactly use gray card? Do you just take photo with gray card on it or is there options on camera to set WB based on that? I have Nikon D5200. Haven't used this feature with it.

I was also wondering if brightness matters? Like would 2700k look as 3100 if it is very bright (such as 2000lm)?

bclaff said:

UnknownSource said:

I am trying to learn if my LED strip I ordered is wrong color or not. I ordered 2700k color bright LED but but visually it looks like 3100k. I am trying to figure out if it just looks like that (3100k instead of 2700k) because I am too close to it or if I actually got wrong color. And when I use android light meter app it also tells me 3100k. I ask because I am wondering if distance affects the color temperature? Like does it come warmer as distance increases or should it stay the same? What is photography standard for checking lightsources? Is there some standard like 1 meter distance from source or any other standard?

Click to expand...

Depending on the camera you have available if you take a raw picture with auto white balance set and open it with something like Adobe Camera Raw (ACR) you'll get a reasonable approximation (using As Shot). I would think certainly good enough to make this distinction.

Click to expand...

FWIW, here's a quick example.

I shot an 18% gray card in open shade and in full late afternoon sun.


Late afternoon sun; a bit warmer than the usual 5000-5500K


Late afternoon open shade; pretty cool but not as high as blue sky.

--
Bill ( Your trusted source for independent sensor data at PhotonsToPhotos )

UnknownSource said:

ACR is Adobe Camera Raw? And how to exactly use gray card? Do you just take photo with gray card on it or is there options on camera to set WB based on that? I have Nikon D5200. Haven't used this feature with it.

Click to expand...

I don't know about the D5200 but on my Nikon DSLR, there's a whole weird procedure for setting a custom white balance that takes 4 pages in the manual. You set the white balance to "PRE" and then shoot a white or gray card; it doesn't take a picture but does store a preset white balance. I never have done it because I shoot RAW.

--
Leonard Migliore

UnknownSource said:

I was also wondering if brightness matters? Like would 2700k look as 3100 if it is very bright (such as 2000lm)?

Click to expand...

No, brightness does not effect color temperature.

Likewise, changing the white balance does not change exposure.

UnknownSource said:

ACR is Adobe Camera Raw? And how to exactly use gray card? Do you just take photo with gray card on it or is there options on camera to set WB based on that? I have Nikon D5200. Haven't used this feature with it.

Click to expand...

An 18% Gray Card can be used for setting white balance and/or exposure. I suppose they've been around as long as light meters. A stack of several sheets of white copier paper, white teflon plumber's tape, etc, can work too.

Here are instructions to setup Preset White Balance for the D5300 which are the same as shown in the D5200 Reference Manual:

https://imaging.nikon.com/support/digitutor/d5300/functions/whitebalance_presetmanual1.html

Darn, it doesn't appear the D5200 (or D5300) will display the resulting color temp after a Preset WB have been set. That's OK, at least the photos won't have a color cast to them.

--
Lance H

lehill said:

UnknownSource said:

ACR is Adobe Camera Raw? And how to exactly use gray card? Do you just take photo with gray card on it or is there options on camera to set WB based on that? I have Nikon D5200. Haven't used this feature with it.

Click to expand...

An 18% Gray Card can be used for setting white balance and/or exposure. I suppose they've been around as long as light meters.

Here are instructions to setup Preset White Balance for the D5300 which are the same as shown in the D5200 Reference Manual:

https://imaging.nikon.com/support/digitutor/d5300/functions/whitebalance_presetmanual1.html

Unfortunately, it doesn't appear the D5200 (or D5300) will display the resulting color temp after a Preset WB have been set. That's OK, at least the photos won't have a color cast to them.

Click to expand...

No Nikon camera will tell you the color temperature of the preset.

Since the question is to measure color temperature that's why I suggest auto white balance and letting something like ACR decode the As Shot WB that he gets.

UnknownSource said:

If CRI is bad measure for quality, is there any other specs that would tell if that given LED is good for photography?

Click to expand...

Not that I know of. But some photographers will color calibrate their cameras with specific light sources. Good software will give estimates of light quality.

your android light meter will not be very accurate
A colorimeter will be your most accurate, then a flash light meter, then a DSLR.
You may be able to find a local camera or video shop or video shooting company give you a reading for free, these are expensive equipment.

there is a HUGE difference in the color of 2700k vs 3200k this shold be easy to see