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Cinematography Tip: Control Window Light With ND Gels

Lewis McGregor

Take control of window lighting on your next shoot with ND filters.

Top image via Shutterstock.

Windows are light sources that can work wonders — if you use them correctly. They’re ideal for soft key lights when the camera faces away from them. However, when cameras face windows providing backlight, trouble can arise. Unless you have a large lighting unit that can match the window light, you’re either going to have to drop the subject into a silhouette or expose for the actor which will blow out the window light.

There’s plenty of discussion on whether or not filmmakers should allow window lights to blow out. It’s a highly creative choice, and opinions will always differ. You might be surprised how many films and TV shows let window light clip. Take note next time you’re watching something.

Control Window Light With ND Gels — Lighting

For those who favor controlling window light, you can do so with ND gels.

ND Window Gels

Much like neutral density filters for your lens, ND window film reduces the intensity of window light. Window gels, like camera density filters, come in a variety of different strengths: .3, .6, .9, and 1.2. If you only have the budget to purchase one roll, you’re going to want at least 2-3 (0.6-0.9) stops of density filtration because sunlight is incredibly bright (around 98,000 lux). Several brands offer this gel; one of the most reputable is Rosco. However, at around $120 for a 7-meter roll, you can quickly burn through your budget.

Control Window Light With ND Gels — Window Gel
Image via Lighting Grip Las Vegas.

Attaching the Gel

A common practice is to attach the gel to the outside of the window to conceal its edges. If you decide to do so, it’s paramount to attach the gel firmly to avoid light leaks and prevent the sound of the wind rustling the gel.

If attaching the gel to the outside of the window is not a viable option, you can temporarily bond the film to the window using a cleaning liquid like Windex. In the video tutorial below from Grip Tips, Dave Donaldson explains that it’s important to completely clean the window before placing the ND film, as you want to ensure that film and the window appear seamless.

If you have several large-scale windows to diffuse (and a large enough budget), ND window panels are more efficient. These are solid gels that you affix to a window. However, since they come in specific sizes, you might run into problems with oddly sized windows.

Control Window Light With ND Gels — Margin Call
Image credit: Before the Door Pictures.

There’s an incredibly creative story from the thriller Margin Call. In the scene above, the windows are 50” to 52” wide, while the ND panels were only 48.” John Paino, the production designer, created removable pilasters to hide the gaps.

Once we installed the ND panels, we could take these pilasters and Velcro them against the window,” says DeMarco. “They not only hid the gaps, but they also looked great as vertical window dividers. As exterior lighting changed, particularly at the end of the day, it was a breeze for key grip Caswell Cooke and his crew to quickly change the panels.


What are your thoughts on window light? Let us know in the comments.