Balancing Color for Flash and Ambient Light using Gels

Balancing Color for Flash and Ambient Light using Gels

Flash with 1 CTO plus 1/8 CTOIn the last article Balancing Flash and Ambient Light Using an Incident Light Meter I did not mention color temperature or any correction for the colorcast in the background. There were however requests for it in the comments section, so in this article we will cover three ways of balancing color for flash and ambient light (tungsten yellow/orange which is approximately 3200°K, flash which has a color temperature close to daylight or 5500°K).

Color Temperature Explained

Before you go into the process of correcting color imbalance you will need to understand color temperature. A basic description of color temperature is based on the color characteristics of visible light from warm (yellows) to cool (blues) and the ability to measure this in degrees Kelvin (°K). Degrees Kelvin is a numerical value assigned to the color emitted by a light source. Visualize a lamp filament that is heated using an electric current. It starts off as black and starts getting hot. At a particular point it will become hot enough to start glowing, typically a dark red. As it gets hotter, it will change from dark red to orange to yellow to practically white. It is important to understand that technically, red light has a lower color temperature but is described as warm, while blue light is a higher color temperature but is described as cool. So remember that the terms warm and cool describe color, not temperature. This is a fairly extensive topic but for a quick explanation this should help.

Read more on White Balance and color temperature:

Since warm and cool are colors, we can change their characteristics by modifying color. In lighting we achieve this modification by using various colored gels of varying densities. Lets examine the first and simplest method.

Method One – Using Color Gels on the Flash

Here are two images of the same scene, one using Auto White Balance (AWB) and the next using Daylight White Balance (WB). The daylight WB is 5200°K while the AWB applied 3200°K. Clearly the Daylight WB is too yellow.

Auto WB

Image captured with camera set to Auto White Balance (AWB)

Same scene as above captured with the camera set to Daylight White Balance

Same scene as above captured with the camera set to Daylight White Balance

The Problem

The background room is lit by tungsten bulbs (typically around 3200°K). We will use a flash to light the main subject (approximately 5500°K).  This is a considerable difference that you will need to resolve. So if you can make both the light sources match in color temperature, you can then set the WB on your camera to that, and get a perfectly balanced image.

The Solution

To achieve this balance, you will use a color correction gel on your flash, to match the orange color of the tungsten bulbs. Theoretically both sources will now produce the same color. So if you set your camera’s WB to “tungsten” you will capture the background without any colorcast and it will look neutral. What about your primary subject? Since the flash output has been color modified to “tungsten”, the entire scene will look natural and devoid of any colorcast as long as the lights are close to the color temperature of tungsten.

Color correction is achieved using gels. These gels are manufactured by companies like Roscoe, Lee and ExpoImaging. Gels come in all sizes from large rolls to precut sheets. My preferences are the Rogue Gels made by ExpoImaging as they are the perfect size for flash heads and are attached using an elastic band. Each gel is marked for its strength and light loss. As a starter, for under $10 you can buy sample packs from most lighting supply stores.

Gels that create yellow/orange light are known as CTO gels (Color Temperature Orange). These gels are available in various strengths as follows:

  • 1/8 CTO Converts 5500°K to 4900°K
  • 1/4 CTO Converts 5500°K to 4500°K
  • 1/2 CTO Converts 5500°K to 3800°K
  • 3/4 CTO Converts 5500°K to 3200°K
  • Full CTO Converts 5500°K to 2900°K

I recommend you start with a full CTO and adjust by adding or reducing the color temperature correction by either combining gels or using gels of lesser strength. Since these gels add color they also reduce the amount of light transmitted. Based upon the gel that you are using, you will need to compensate for the loss of light. The typical light loss is mentioned in “f” stops with each gel strength. This information is typically imprinted on the gel or provided on a backing sheet of paper. You should use this information as an initial guideline for compensating your exposure.

This method will work reasonably well. However, it is not the most accurate, as it relies purely on a visual color correction. See the result in the following image:

The camera White Balance is set to Tungsten and the flash is gelled using a Full CTO

The camera White Balance is set to Tungsten and the flash is gelled using a Full CTO

Notice that the color of the subject is fairly accurate but the background is still a bit yellow/orange. The color temperature of the lights in the background may not be true 3200°K.

Method Two – Gels on the Ambient Light Source

In the second method, you will use gels over the offending lights if at all feasible. In this example consider it not feasible. However, you can use additional flash heads to overcome the problem of the tungsten colorcast. You do this by applying an opposing color gel to one or more flash light sources to fill the background. Keep in mind that based upon the size or the area and the intensity of the ambient light in the background, this too may not always be feasible. Take the additional flashheads (make sure they can be fired as slaves) and put a CTB (Color Temperature Blue) gel on each. What you are attempting to do is to negate the effect of the Tungsten by adding blue light to the ambient environment. Test your exposure and set the camera to “flash” white balance. Once again, you may need to add or subtract the gel intensity.

The set up. Note how the flash heads are concealed from view

The set up: note how the flash heads are concealed from view and pointed into the room that is the background

The CTB gels like CTO gels are available in multiple strengths as follows:

  • 1/8 CTB Boosts 3200°K to 3300°K
  • 1/4 CTO Boosts 3200°K to 3500°K
  • 1/2 CTO Boosts 3200°K to 3800°K
  • 3/4 CTO Boosts 3200°K to 4100°K
  • Full CTO Boosts 3200°K to near daylight

Once you are satisfied with the background color, go ahead and photograph the primary subject. Do not gel the main flash and leave the white balance on “flash”.

Color Bal

Color Correction using blue gels in the background

In each of the cases above there is still some color cast in the final image. This is because the lights in the background are not true 3200°K and we have been relying on tungsten color temperature for our corrections.

Method Three – Custom White Balance for Background and Matching Gels on Flash

Here you use custom white balance to establish an exact white balance setting for the ambient light. It is best to use a “white balance card” or a device like the X-Rite Color Checker Passport.

Color Checker Passport in Ambient Light

Image captured of  a Color Checker Passport in ambient light

Zoomed in for creating a Custom White Balance

Color Checker Passport – Zoomed in for creating a Custom White Balance

Image of the Color Checker Passport after Custom White Balance was established

Image of the Color Checker Passport after Custom White Balance was established

If possible, bring that image into Lightroom or Adobe Camera Raw and determine the actual color temperature. In this case, it is 2400°K, which, as you can see, is vastly different from the 3200°K tungsten. No wonder there was still a yellow colorcast in the first method. Use this measurement to establish the gel strength needed for the primary flash. If you cannot use Lightroom or any other software to obtain an accurate color temperature reading, you will need to do a bit of trial and error to determine how much CTO to use. In this case we need to get to 2400°K. A full CTO will drop 5500°K to 3200°K and a 1/8 CTO will drop an additional 600°K bringing the correction to 2600°K which is fairly close to what we need. Leave the camera set to the custom WB and gel the flash with one Full CTO gel and one 1/8 CTO gel to get a well balanced image.

The correct White Balance for the background

The correct White Balance for the background

Using a Full CTO on flash head

Using a Full CTO on flash head

Flas with 1 CTO plus 1/8 CTO

Flash with a Full CTO plus a 1/8 CTO – a well color balanced image

One full CTO and one 1/4 CTO – the subject is a bit warm

One full CTO and one 1/4 CTO – the subject is a bit warm

In Conclusion

Always keep a set of color correction gels in your bag if you use flash on location.  Not only will you need them for indoor flash photography but the CTO gels are a ideal when using flash for portraiture at sunrise or sunset.

Read more from our Tips & Tutorials category.

Shiv Verma is a photographer, educator and technologist and lives in Wrentham Massachusetts. He is an avid wildlife and commercial photographer and conducts photo workshops and tours worldwide. You can check out more of his work on his website.

  • Gr8Ray

    What caused the alternating green dots under the subject’s ear? They seem to match the pattern of the lights in the background. I’ve noticed similar artifacts in my photos when using filters on my lenses.

  • http://www.shivverma.com/ Shiv Verma

    There is a large bay window behind the camera and front left of the mannequin that is causing the reflection. I could have cleaned it up but did not want to do any post processing for this demo.

  • Gr8Ray

    The timing of this article was great for me. I’m in the middle of reading Syl Arena’s “Speedliter’s Handbook” and had started looking for a good starter set of gel’s for a novice user. I went ahead and pulled the trigger on the Rogue CC gel kit based on your recommendation.

  • http://www.shivverma.com/ Shiv Verma

    They are excellent gels and well constructed. Enjoy Syl’s book – he is a great educator.

  • Curt Clayton

    Great post! In the days of shooting transparency film it was rare to do an interior shoot without CC filters on the lens and gels on our lights, and a color meter was a must. Seems that very few photographers are using gels today but instead will try to color correct everything in Photoshop. It’s so much better to get the color right when making the exposure! In addition to the CTO gels listed in the post, a sheet of Rosco Windowgreen is very handy. A small piece over the front of a speed light (or studio flash) will balance the flash very nicely with the cool white florescent lighting used in many office and event spaces. Just set your cameras white balance to florescent and you’ll have nice clean color throughout.
    http://www.claytonstudio.com

  • http://www.shivverma.com/ Shiv Verma

    Thank for the comment Curt. It is unfortunate but true about “trying” to fix it in post….. I would rather be shooting it well rather than spend time in post. Thanks for the Window Green tip. We try and keep these articles to a word count limit so we don’t loose the reader. The Rogue gels do come with Window Green and a few additional goodies. Regards

  • http://arjunkarthaphotography.com/ Arjun Kartha

    Great read! I’ve faced similar problems when trying to balance daylight through a window and warm indoor lighting when shooting on location. Will definitely invest in good quality gels after reading this article. Thanks for writing this!

  • http://www.shivverma.com/ Shiv Verma

    You are most welcome Arjun and thanks for your kind words. Regards

  • Photography by James

    I have found a great app for the iphone and ipad called Light Spectrum Pro. It turns your iOS device into a colour temperature meter. You can then calculate the filter you need to apply. Well worth checking out.

  • http://www.shivverma.com/ Shiv Verma

    Thank you James. I had heard about it but have not tried it. The reviews on the App store are not favorable at all.

  • Rockape

    Sorry but being English I have no idea what this gel you use is, I use gel as a healing cream, so what is this gel you use on a flash gun/ camera? Must get some as results look great.

  • Keith Starkey

    I am afraid I didn’t follow method 3.
    The method states, “Here you use custom white balance to establish an exact white balance setting for the ambient light.” A WB of a warmer level is figured for the background (2400 is warmer than 3200, correct?), and then the attempt to match the WB for the subject. So, what’s going on with the figuring of the WB for the ambient light? Why warmer? And why is this a correct WB.

  • http://www.shivverma.com/ Shiv Verma

    Hello Rockape, These are similar to filters. Originally they were made from gelatin but now are synthetic – in the UK they are distributed by Flaghead Photographic and available form Amazon UK too.

  • http://www.shivverma.com/ Shiv Verma

    Hi Keith, The custom white balance established the exact temperature of the background. You then use Lightroom to read the temperature. Use tis reading to balance the flash by adding gels to obtain a Kelvin reading that is close to the custom white balance.

  • http://www.shivverma.com/ Shiv Verma

    Keep in consideration that the flash is 5500 Kelvin we need it be warmed up to 2400 Kelvin in the example.

  • Keith Starkey

    Hi Shiv. I’m still confused. According to the layout of the third method, the correct WB for the background was WARMER (2400 Kelvin) than it already was (3200). So, shouldn’t that have made the background even more orange/yellow? (Additionally, the photo shows the “corrected” WB more cooler, not warmer.) Finally, was the thinking process, so to speak, of the X-Rite Color Checker Passport along the lines of, “okay, this is too warm of a WB, so I’ll give a cooler number to correct it”? If so, again, I’m confused: the correct WB was warmer.
    Thanks much.

  • http://www.shivverma.com/ Shiv Verma

    Lets take it from the top. The background lights are tungsten. Setting tungsten WB would be 3200K but in reality the lights are not true 3200K but 2400K as indicated by white balancing using the color checker passport. Now the flash is 5500K so it need to we warmed to 2400K or there about. One full CTO plus a 1/8 CTO on the flaw will drop the Kelvins to 2600K which is close to the 2400K of the background. Both foreground and background are 2400K-2600K. The camera WB is at 2600 K all three are dealing with the same temperature. If you want to discuss, call me 617.759.0010

  • Keith Starkey

    Thanks so much!

  • http://www.shivverma.com/ Shiv Verma

    It was a pleasure speaking with you and hope I was of some help. Regards.

  • France Quirion

    Hello Mr Verma, many thanks for your very enlighten post. I’m doing those learnings at this time and still asking me a lot of questions. What do you think it will happen if i shoot raw, gel my flash with a CTO gel under tungstene light and let my camera on AWB? Using raw, is-it necessary to gel our flash in very low color temperature? I much like to shoot in windows, and sometimes the light seems to be half natural daylight in some home and half tungstene, what do do you think will be the better solution in these circumstances?
    France Quirion, Québec, Canada

  • http://www.shivverma.com/ Shiv Verma

    Hello Mr. Quirion, Thank you for your comments. As to the question you ask and hopefully I have understood here is the answer. If you are in a place that has tungsten alight then set the camera’s white balance to tungsten and gel the flaw with CTO Gels. You can then use the camera raw converter to adjust as needed.. If the color temperature is not extreme then it is best to take one image with a white balance card or a color checker device and then use the eye dropper tool in Lightroom to identify the temperature using this as the reference. Next you can synchronize the settings for all the remaining images in that sequence or theta light situation.
    Hope this helps.

  • France Quirion

    Many thanks for your time! I’ll try all your solutions and will see how it turns.

  • Barry E Warren

    Great Read and thanks for sharing. This gave me a better understanding of how to use the gels I have.

  • http://www.shivverma.com/ Shiv Verma

    Thank you Barry – I am glad this helped.

  • Anjolie

    Hi Shiv
    Warm Greetings!
    Thank you so much as you have well explained the subject. I have a query – when using flash in an event if a videographer uses sun gun at his convinience it gives yellow cast in the photos shoot in that particular span of time. How do I overcome this problem just changing the kelvin settings?
    Regards,
    Anjolie

  • http://www.shivverma.com/ Shiv Verma

    Hi Anjolie,
    Thank for your kind words. The best way is to adjust the kelvin settings to get the white balance correct. If you do have the ability to take an image with a color checker passport or even a white card in the same light, you can use that as a reference to adjust the kelvin setting. If you use Lightroom or Adobe Camera Raw this becomes very easy as you use the eye dropper tool to select the temperature.
    Regards,
    Shiv

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