The first time I set up my new LED panel for a shoot I realized I didn’t have a good procedure worked out for matching the color temperature of the ambient light. My new panel is the Aputure Light Storm LS 1c which is a bicolor panel. I chose it partially for the ability to set any desired color temperature between 3200K and 5500K. I like having the flexibility to dial in the color temperature to match the ambient light without having to bother with gels. I had figured it would be easy to do with the new panel but I hadn’t actually thought through the workflow.
I knew I could always eyeball it and that would get me close enough for lots of purposes. But I was looking for a more objective, reproducible process. Of course, there’s the obvious idea of using a color temperature meter but those meters are expensive and are not an option for me. For a while, as I thought about other possible methods to accurately match ambient or practical lighting I was stumped.
Leveraging the Panasonic GH4’s White Balance Features
I shoot with a Panasonic Lumix GH4 and you can always set a custom white balance using a gray card. That would allow me to get an accurate balance with the ambient lighting but I’d have no way of knowing what color temperature the camera was using. I need the Kelvin temperature in order to dial it into the LED panel controller. I thought about this problem, off and on, for a couple of days and eventually came up with a procedure that’s pretty accurate and objective. My procedure still relies on using the eye to determine a match but I think it’s more accurate than trying to judge a match by dialing the light temperature up and down and watching its effect on the scene.
Instead, what I do is compare two images on the GH4. One is a white-balanced image that I set for the ambient lighting conditions using the GH4’s custom white balance. The other is a test image with its white balance set using the GH4’s Kelvin white balance mode. By adjusting the Kelvin white balance up and down and comparing that image with the custom white-balanced image it’s possible to get very close to the correct Kelvin temperature. Once you have the number you can dial it into the LED panel.
Step-by-step White Balance Matching
Here’s the procedure I use:
- Set a custom white balance using a gray card for custom white balance slot #4. (You can use any slot from 1-4 but it’s easiest to compare the custom white balance to the Kelvin image using slot #4. With #4 you can instantly flip back and forth between the two.)
- Switch to white balance Kelvin mode. Set the temperature as close as possible by guesstimating. Then switch to your custom white balance #4 and compare the view of the gray card.
- Switch back and forth between #4 and K to see if the K image is bluer or yellower. If bluer increase the K value. If yellower, decrease the color temp. When the two images match the value shown in the K version is the actual color temp which you can use to set your lights.
How Closely Does the Color Match?
The technique didn’t yield perfect results. The more I increased the power of the LED panel the more blue the light became. At 50% power the blue shift is noticeable. There could be various reasons why this is happening. One is the possibility that the GH4’s custom white balance is set to a finer granularity than the 100° K steps provided in the camera’s Kelvin white balance option. If the GH4’s custom white balance were to set the temperature to 5250 the closest I could match it with the Kelvin settings would be 5200 or 5300. The same limitation applies to the light panel which only adjusts in 100° steps. Another explanation is the possibility that the light panel’s color changes as the power level is changed.
Of course, you can always adjust in post particularly if shooting stills in raw format. But, it’s better to get it right in camera and this is my attempt at doing just that. I feel like this approach gets me a closer match than just looking at the scene and guesstimating as I change the light panel’s color temperature.
And, in this example, by the time I got to the 50% power level the LED panel was overpowering the ambient light level. Once you reach that point you can more or less ignore the ambient light and set your color balance to match the LED panel’s color.
This technique doesn’t depend on the absolute accuracy of the color in the GH4’s LCD panel or EVF. Because I’m comparing two images the important thing is to get the same appearance on both. The camera’s LCD panel could be adjusted way off of true color but as long as the two images match the Kelvin readout should be accurate (as accurate as the GH4’s white balance features make possible, anyway).
Fine-Tuning the Process
For a more careful comparison of different white balance settings I like to use the EVF instead of the LCD panel. That avoids any interference from the room light or objects in it.
A way to get a more detailed look at the color balance is to take a couple of test shots. You can first choose one white balance setting and snap a shot. Then, switch to another setting and snap again. Then, in playback mode you can switch between the two. This way you can zoom in and look carefully at the details of your scene.
Brighter Light Storm
One note about the Light Storm: Aputure also makes another very similar model, the LS 1s, which is a single temperature light, daylight-balanced at 5500K. The advantage of the LS 1s is that it it’s a bit brighter than the bicolor 1c. So, if you don’t need the ability to adjust color temperature you may prefer the 1s.