Mixed Light Sources: Let’s Fix It!

Steven Heller Tutorials 0 Comments

Looking for a quick summary of the following info? Scroll to the bottom for the TL;DR version.

When I do my two point lighting setup, working with house lights or ambient light can be tricky. As mentioned in my previous post it can make for a great diffused fill light, but you often run into problems with mixed light color temperatures. I wan’t to avoid getting into the details of lighting temperature too much as many people much smarter than me have already covered this. Suffice it to say, that if you’re not careful, mixing lights with different color temperatures can cause big problems down the line when you’re looking to color correct your finished work. You will likely end up having parts of your frame that are cooler (more blue) or warmer (more yellow) than you would like and they are quite often a PAIN to try and fix. So, instead of being reactive, let’s be proactive and fix the problem before the light even hits the lens.

Lighting gels! Needed for working with mixed light.

Gels! These ones range from CTO (left) to CTB (right).

Let’s start off by looking at your lights. I use daylight balanced lights so both the lights in my 2 point setup are the same color. Using matching lights really helps simplify things. For reference, daylight balanced lights are around 5000K (K = Kelvin). The color temperature of fluorescent lights, for example, are around 3000K. What we want to do is try and get our lights and the fluorescent lights to look as close to the same as possible. Changing the color temperature of the overhead fluorescent lights, while it can be done, would be a lot of work. So, our best option is to change the color temperature of our lights. There are LED lights out there that will let change the balance of the light just by turning a knob. How convenient! But there is a price for this convenience. An LED panel generally consists of a whole bunch of small LEDs. LEDs are one color temperature, so what the light manufacturers will do is make rows daylight balanced (roughly 5000K) and the alternating rows will be tungsten balanced (about 3200K). A knob will allow you to shift the balance of color by raising the brightness of the daylight rows, while simultaneously lowering the brightness of the tungsten rows, and vice versa. This will give you the ability to shift light from 3200K to 5000K. Th problem with this is that when you have your light set to full daylight, you’re only using half the rows of the panel, thus half the brightness. The panel could be twice as bright if it used all the rows of LEDs (unless there’s some sort of roll off or something that wouldn’t make it exactly twice as bright. I don’t know. There’s probably some math involved in there somewhere).

But let’s assume that you’re using daylight balanced lights like me. So, how do you change the color of the lights? If you’ve never met, meet my little friends, Gels. Gels are translucent sheets of colored plastic films that are a very specific color to help you with your lighting. Gels come in all sorts of varieties but the ones that I use, and if you’re using daylight balanced lights in corporate environments you will be too, are CTO gels. CTO stands for “color temperature orange”. These gels will warm your daylight balanced lights to match fluorescents. To confuse things even further, CTO gels come in several varieties. Full CTO, 3/4 CTO, 1/2, CTO, 1/4 CTO, and 1/8 CTO. A full CTO gel is the gel that would be used to convert a daylight balanced light to match a tungsten light. I personally carry with me some 1/8 CTO and some 1/4 CTO. Gels can be combined as well. So if you only have 1/4 CTO but need a 1/2 CTO, you can layer two 1/4 CTO gels for the same effect.

Ambient lighting temperature. Let's get ready for mixed light!

Camera reads 3000K using just the overhead lights.

Mixed light with a daylight balanced light added.

Adding a daylight balanced light brought the camera WB reading to 3800K.

Now that you understand what gels are, let me show you how I use them in a practical situation. The first thing that I do is get my cameras and lights setup so that I’m pleased with the look of everything. With my lights off and the house lights on, I’ll white balance my camera. Now, this only really works if your camera will allow a custom white balance, and if it will show you the Kelvin temperature in camera. A word on white balancing. There’s several ways to white balance a camera. One is to use a white or gray card. This works great. Just make sure to hold the card in the light that you’re trying to get a reading from. I’ve started using a white balance filter. It’s an opaque white plastic filter that allows light to pass through it. Your camera will balance to the white of the filter, which is colored only by the light in the room. When you white balance your camera to the ambient light in the room, this is the temperature that you need your lights to match, so take note of it. Now, bring on one of your lights. A word of disclaimer: if any gaffers are reading this, please forgive me. I have no doubt that I’m violating several written and unwritten rules of gaffer-dom. For this I make no apologies. When you have to shoot, light, run sound, etc… all by your lonesome, sometimes you just need to get things done quickly. This method has worked great for me, so I feel inclined to share. Okay, back to the show. Now that you have one light on, white balance your camera again. Your kelvin reading on your camera will have changed because it now has a new light source thrown into the mix. Your goal is to add CTO gel to your light to get your camera to show the same (or as close as possible) white balance reading that it did with only the room lights on. This is a process. I usually start with 1/4 or 1/8 CTO and white balance again. If it brings you close, but not close enough, add another gel. Keep doing this until the white balance matches the reading that you took without your lights on. Once you have it matching, now it’s time to turn on your second light. Since it’s also daylight balanced, add the same amount of CTO gel that you put on your first light and it should get you there, but check your white balance readings to make sure.

Fully lit scene with gels on lighting. No more mixed light!

The fully lit scene with daylight balanced lights matching the overhead fluorescents. The camera now reads 3000K, like it did with just the house lights.

Lighting gel in place

Make sure your gel covers the entire surface of the light. Gels will melt, so if your light gets hot, make sure they’re not in contact.

If you’ve done everything correctly, your lights should pretty closely match the room lights. Now you’ll find that your footage is MUCH easier to color correct as mixed light no longer exists. One caveat to all of this: some people like to have their edge/hair light a little warmer. If this is the case, you may need to add a bit more gel to that light to warm it up. Just something to consider. Caveat #2: adding gels will decrease the amount of light that passes through, so you’ll need to make your lights a little brighter to compensate.

Whew! This was a long one. I’m sure I’ve confused many people reading this and for that I’m truly sorry. Please don’t hesitate to leave a comment asking for clarification.

 

Working With Mixed Light – TL;DR

Ambient light is most likely a different color temperature than your set light. Use gels to balance it out.

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