Intro to Using Gels to Correct Color Temperature
Gels are cheap but powerful tools to help you work accurately and creatively with color temperature. Many beginning photographers may set their camera to AWB (auto white balance) and never think about white balance again. However, taking the reigns of your white balance settings is an important tool to improve your flash photography.
Accurate white balance depends on the color temperature of the scene. To have technically correct white balance, the color white is represented as perfectly white in your image. This is part of why many photographers take a photo of a grey or white card as a reference to later use to adjust the raw image for white balance later. Many also may just shoot on AWB.
When using flash it becomes important to choose your own white balance because the white balance of the flash may not match the white balance of the ambient scene. The white balance not only changes throughout the day as the sun goes from the horizon to the center of the sky, but you will also find different white balance on a cloudy day or in deep shadow or shadows.
To set your camera’s white balance you must consider the "color temperature" of a light source, which refers to the relative warmth or coolness of white light. Imagine the spectrum of color temperature measured in Kelvin going from “candle” (the warmest) to “dusk” or “moonlight” (the coolest).
Daylight White Balance
The color of each flash will vary slightly depending on quality and consistency but is generally very very close to daylight which is 5500K.. Your camera’s flash or strobe white balance icon in your menu generally looks like a flash or lightning bolt. The first step to shooting with flash should be to set your white balance to that setting.
If your entire scene is illuminated by flash, or you are shooting flash mixed with midday daylight on a sunny day, then you are shooting in an accurate way. The actual range of daylight white balances in ambient light is between 5000K-6500K.
Match Camera WB to Ambient
What if it’s a cloudy day, or what if you’re shooting indoors with artificial lighting like tungsten bulbs? The general rule when shooting in a natural style is to first dial your camera’s white balance setting to the ambient lighting. Then, you gel the lights to match the ambient color temperature.
Gelling for an Overcast Day
One of the most common and easy situations where a gel can improve your photos is lighting on a cloudy day or in the deep shade. The white balance of a cloudy day is very different than that of a flash, which is balanced for daylight.
When shooting with flash in the shade or an overcast day, set your camera to the appropriate setting for the ambient lighting - in this case, dial your camera’s white balance to approximately 6800K to match the ambient light.
A flash with no gel will appear too reddish-orange at this point. If you try to fix the problem by setting the white balance to flash, the background will appear too cool and bluish. The correct fix is to gel the light by attaching a CTB (color temperature blue) gel.
A ½ CTB gel should be the appropriate correction for the difference between daylight and deep overcast or deep shadow. If it’s a cloudy day with partial sun breaking through or you are only in light shadows, you may only need ¼ CTB.
Gels and Golden Hour
Another scenario where gels can make a big improvement in your flash photography is at sunset. At sunset, the color temperature is because the sunlight is going through many more dust particles.
©Laura Barisonzi Photography This image shot at sunrise shows a flash firing at 5500 with no gel. The flash appears far too cool.
©Laura Barisonzi Photography Here the flash is correctly gelled to match the golden hour light.
When taking portraits at golden hour, the approach is basically the same as in the shadows but with orange instead of blue. Set your camera’s WB to approximately 2500K. A flash with no gel will appear far too reddish orange at this point. Now use a cto gel (color temperature orange). ½ CTO gel is a good point to start but you may end using a full CTO. Now the color temperature of the sunset and flash will be much closer. If you want to warm the white balance later for creative mood you can do that with the white balance slider in Lightroom but at least you will affect the entire photo including the flash lit areas evenly.
©Laura Barisonzi Photography. Here the flash is correctly gelled to match the golden hour light.
Every gel has some amount of light loss meaning the color gels will cut total output from your flash. The reduction depends on whether the gel is ¼, ½ or full. Generally with ¼ CTB you will see approximately ⅓ a stop reduction in your light output. Also, if you are using TTL metering you will need to manually adjust the output of your light because the TTL will not measure your gel.
©Laura Barisonzi Photography
Mixed Color Casts
When you are mixing flash and ambient lighting with two different color temperatures often you will see a different white balance in the shadows then you see in the lit area. Skin may appear too orange or shadows too blue. If shooting indoors the shadows may look too green. Now that you know to look for these, these discrepancies in your LCD while your shooting should be an alarm bell to consider using a gel on your flash.
Fighting Green Casts
The reason shadows on the face may look green when shooting indoor portraits is the inherent green in fluorescent lighting. The green comes from an inconsistency in tint that comes from indoor fluorescent lights. If the light is green enough you may need to add green color gels to your strobe. This is less common now that LEDs are more widely used.
Purchasing and Attaching Gels
Though you can start out attaching gels with gaff tape, however the tape can melt as your flash heats up. Some gels are custom made shaped for the light and can just slide into a speedlight. If you purchase a kit of MagMod Gels for Speedlights then the MagMod MagGel Holder can be a convenient solution.
©Laura Barisonzi Photography
Gels are Cheap!
Large individual sheets of gels are only about $7-9 each from manufacturers like Lee like Lee Filters 1/2 CTO 24x21" Gel Filter Sheet and it is easy to cut them yourself. For larger strobes, one option is to attach gels with rubber bands or silicone rubber bands like the Flashgels Add-On High Temp Rubber Band Kit which have less chance of melting.
Color temperature gels are colored pieces of plastic that can completely transform the way you use flash lighting. One of the cheapest and most powerful accessories in photography, there is no reason not to learn the fundamentals of color balancing for your flash with gels.
This article was guest authored by our collaborator Laura Barisonzi.
Laura is an advertising portrait and lifestyle photographer based in New York, NY.