Matching light source temperature

[Christian Thomas]

Hi everyone.

I would like to match different continuous light sources using color gels. However, I don't know exactly how to do that since I don't know what's the color temperature of each light source.

In theory, one light source is 5400K and the other is a tungsten 3200K. How can I properly measure them? Should I buy a color meter? Can you give me some advice?

Gels come in different flavors and I saw that they come with different light transmission and color intensity. But even if I'll find out what's the correct color temperature of my light, I don't know which gels to buy. Can you give some advice?

Thank you.
Best.

[chauncey]

Correct color temperature, IMHO, is highly overrated...the only time it concerns me is when shooting
people and in that situation I use one of these...http://xritephoto.com/colorchecker-passport-photo

I've never used gels but do use colored LED lighting, in which case I shoot in Live View and adjust
lighting accordingly...or in LR.

[george013]

Hi everyone.

I would like to match different continuous light sources using color gels. However, I don't know exactly how to do that since I don't know what's the color temperature of each light source.

In theory, one light source is 5400K and the other is a tungsten 3200K. How can I properly measure them? Should I buy a color meter? Can you give me some advice?

Gels come in different flavors and I saw that they come with different light transmission and color intensity. But even if I'll find out what's the correct color temperature of my light, I don't know which gels to buy. Can you give some advice?

Thank you.
Best.

A tip somebody gave me once. Make a WB-preset with the camera pointing at the lightsource and the lens covered with a white tissue. If you're lucky the camera might give you a colour temperature. Nikon does do it.

George

[Mike Buckley]

In theory, one light source is 5400K and the other is a tungsten 3200K.

I would simply go with the rated temperature and use the corresponding gel recommended by the manufacturer of the tungsten light source (see below) to convert to daylight, which is close enough to 5400K. Even if the tungsten lamp's output is not exactly as rated, I doubt that it will be so far off that it will adversely affect your images. You might even be able to Google the standard gel to use in this situation.

Naturally, the need for a color-correcting gel should exist only when you are using multiple light sources of different Kelvin temperatures at the same time and when you don't want to exploit the resulting look of the multiple temperatures for artistic effect.

But even if I'll find out what's the correct color temperature of my light, I don't know which gels to buy.

The manufacturer of the light source will probably provide the specification of the gel to use. It might refer to one of the types mentioned in the following excerpt from Wikipedia: "The main color correction gels are CTB (color temperature blue) and CTO (color temperature orange). A CTB gel converts tungsten light to 'daylight' color. A CTO gel performs the reverse.[2] Note that different manufacturers' gels yield slightly different colors. As well, there is no precise definition of the color of daylight since it varies depending on the location (latitude, dust, pollution) and the time of day.

"Gels that remove the green cast of fluorescent lights are called minus green. Gels that add a green cast are called plus green.[2] Fractions such as 3/4, 1/2, 1/4, and 1/8 indicate the strength of a gel. A 1/2 CTO gel is half the strength of a (full) CTO gel."

[Mike Buckley]

Correct color temperature, IMHO, is highly overrated

My experience is that it's a matter of understanding when correction is and isn't important. Unless the photographer is going for an artistic effect that is explicitly the result of multiple color temperatures lighting a scene, it's very important when using more than one color temperature at a time to control the color temperature. The title of the thread refers to matching light sources and the first post refers to two color temperatures, so I infer that the OP wants to correct one of them so the final lighting of the scene is done using just one Kelvin temperature.

[Dave Humphries]

Hi Christan,

Unless you also have significant daylight in the room, I'd suggest gelling the 5400 light source to tungsten with a CTO - two reasons:

1) I suspect the 5400 light source will run cooler than the tungsten, so (I think) you're less likely to run in to problems with melting the gel (or worse!) if it is front of a (usually very) hot tungsten lamp (especially if one of those reflector halogen jobbies.

2) I think the CTO gel will absorb less of your light than the CTB

If you do use CTO on the 5400 light, you must obviously set the camera to Tungsten WB when shooting.

However, I am not well practised shooting with continuous light sources, Mike is - Mike, which way round would you do it?


Can't help feeling that just getting two of the same light might solve a lot of problems though - and I would not choose tungsten.

HTH, Dave

[Loose Canon]

One possibility of determining this Christian is if you have a photo editor it may show you the color temp.

For example, with Adobe Camera Raw (and Lightroom I’m pretty sure). You could shoot a RAW file of neutral gray card under the light in question. And only under that light with no other light influences. Open the file in ACR (or Lightroom) and take the color balance tool (eyedropper tool), click on the card, and it will give you the color temperature.

If you are using hot continuous bulbs be careful about using gels!

[Mike Buckley]

Can't help feeling that just getting two of the same light might solve a lot of problems though - and I would not choose tungsten.

I agree with that unless there is a compelling reason to use the tungsten lamp. (I have an old, used one and thought I had a compelling reason to buy it. I later learned that I actually have no use for it, at least not so far, and have never made a photo using it.)

I actually don't know whether it would be better to add a gel to the 5400K lamp or the tungsten lamp. I probably spoke out of turn when suggesting adding the gel to the tungsten lamp. As Dave suggested, it would certainly be easier to add the gell to the 5400K lamp because you don't have to be concerned about heat, assuming that lamp is a compact flourescent lamp. If you do decide to add a gel to the tungsten lamp, you can purchase a frame that holds it far enough away that heat is not concerned. See this frame as an example. The cost of the frame alone might be the motivation you need to add the gel to the 5400K lamp.

[Manfred M]

Christian - let me come at it from a slightly different direction to the excellent advice you have received so far. In most of my photography work I tend to use gels to introduce specific colours to the image, but in my video work I will use gelled lights for colour balance purposes as well.

As a general rule, most people try to avoid the situation you find yourself in because they will try to work with colour matched lighting. It's definitely an easier solution that what you are trying to do. That being said, I have gone both ways with CTO and CTB (Colour Temperature Orange and Colour Temperature Blue) gels. I have sets of both ranging from 1/4 cut to 2x and I play around with them to get the effect I want (sometimes normal and sometimes funky). The fractional cuts are often better when used on a dimmer light source versus the normal colour temperature out of the key light. When I use the gels on my "hot" halogen lights, I use barn doors on the light and clip the gels to the barn doors to ensure that the gels don't melt or burn.

My preference is to balance the tungsten light to daylight, rather than cool the daylight source to tungsten. While this might sound a bit counter-intuitive, there is a good reason to do so and that is the human visual system. Our visual system is far more sensitive to colour temperature differences at lower colour temperatures. We have no issues at all noticing differences between, say 3000K and 3300K, but most people won't notice a lot of difference between a 5600K light and a 6000K light, so increasing the tungsten colour temperature (with CTB) has some advantages when you try to create a more balanced light. By the way, as you tend to have one key light, the fill lights or other secondary light sources can be off a bit on colour temperature without having a significant impact on the final product; how much you can get away with will take a judgement call on your part.

If you are shooting with fluorescent lights (including compact fluorescents) that are not daylight balanced, try using CTS (Colour Temperature Straw) gels. They are often most effective with that type of light source.

[Loose Canon]

Seems like a strange OP Manfred. And Christian?

Using continuous indicates a studio setting. Nothing has been mentioned about video and this is a still-shot Forum. Further, the OP mentioned buying a ”color meter”. And further still, why purchase gels, color meters, etc. to attempt to correct a problem that has been created and throw money in a wrong direction when a couple of bucks could solve a continuous light solution by at least attempting to throw that money into a balanced system? Continous bulbs and fixtures are cheap and pretty easy to match! In under $20 USA one may have a box of matching bulbs, fixtures, and reflectors if one wants continuous lighting. No worries about matching. Just shoot and color balance in post if needed. And why not do this instead of struggling to balance unbalanced lighting every time one wants to shoot using these lights?

I look forward to the OP’s continued participation.

[Manfred M]

Terry - the reason I use the video experience is that shooting with hot lights is very similar to shooting with continuous lights for still studio photography in jpeg. That means you need to nail the white balance as it can't be corrected in post. There is no equivalent of raw in video - it's always compressed and the white balance setting is baked in. Doing a custom white balance for every scene is quite common in video work.

I quite agree that the right solution is to avoid mixed lighting if at all possible and the most elegant solution is to use lights that are all the same colour temperature.

[Christian Thomas]

Thank you very much for your tips. Very helpful.
I didn't know color meters were so expensives, I would rather avoid mixing different colour temperature, however sometimes is not possible.
Thank you again.
Best.

[george013]

Thank you very much for your tips. Very helpful.
I didn't know color meters were so expensives, I would rather avoid mixing different colour temperature, however sometimes is not possible.
Thank you again.
Best.

You already have a color meter. Your digital camera.

George

[Manfred M]

I would rather avoid mixing different colour temperature, however sometimes is not possible.

On the other hand, in studio work, which is what you appear to be describing in your initial question, it is best to avoid it.

Outside of the studio environment, especially in artificial light environments, there I would have to agree with you.