Relaying Light: Using Diffusion to “Fix” Natural Light

Diffusion doesn’t just soften light; it relays light. Here’s how I used a large piece of dense diffusion to light the inside of a car and hide the little known fact that the sun moves.

This spot was the first in a series of six that I shot two years ago for OnLive, a company that specializes in streaming gameplay over the Internet. They went through some rough times but now they’re back and they’ve decided to release these spots as part of a new ad campaign.

My lighting budget had to cover the needs of all six spots over five days, so I had to build an equipment package that worked for everything. This car was the only location that would normally have required some big lights to balance a dark car interior with a day-lit exterior and keep the quality and direction of light consistent over time, but we didn’t have the money for a generator and a couple of large HMIs. Fortunately I had two tricks up my sleeve: an Arri Alexa and a 12’x12′ frame of full grid cloth.

First, here’s the spot:

It’s only two shots but we shot long and short versions, along with several script variations, over the course of a morning, and they all had to match visually as we didn’t know exactly which shots would end up next to each other. We had a street in San Francisco to ourselves, and luckily it ran east/west. This became key to my cunning lighting plan.

A few years ago I discovered that the best way to relay light through windows is to cover them with diffusion. (Diffusion is generally thought of softening a light source, but what it’s really doing is catching light from another light source and transforming it, both in quality and reach.) I was tasked with shooting inside the nose section of a 747 aircraft, and I didn’t have the time or budget to line up a series of massive HMIs to ram soft light through several tiny windows. At some point I realized that the aircraft faced east/west, so one side always faced south toward the sun. The trick was getting the sun inside the plane: hard sunlight coming through a window creates a very bright pool of light but that pool is very confined, plus it moves with the sun. Going with natural light meant I’d get a series of hot spots that moved across the cabin over the course of the day, and that wasn’t appropriate to the story at all. It would also look plain sloppy.

I covered all the windows on the south side of the aircraft with Lee 216, which is a very thick white plastic diffusion. Instead of the sun lighting the inside of the plane directly–which wasn’t going to happen–the sunlight made the white diffusion glow, and that glow lit the inside of the aircraft. The effect is the same as if I’d put a light outside every window. In this case, though, I used one big light that moved across the sky all day long–but no one inside the plane saw that, as diffusion glows the same regardless of the angle from which it’s lit.

In a way I used the diffusion to relay the light of the sun. The sun lit the diffusion, and the diffusion became a light source that lit the inside of the plane. The people closest to the windows got a bit more light than those seated farther away, but as we expect this to happen with windows it wasn’t immediately obvious that I’d simply covered them all with white plastic. Also, the light from the diffusion didn’t change at all for most of the day: although the sunlight moved in relation to the plane the inside of the plane stayed constant as thick white diffusion radiates light in exactly the same way whether it’s lit from dead on or at a steep angle.

I used the same trick for this OnLive spot. I had the car positioned so that it faced east, and then we rigged a 12’x12′ frame of grid cloth over the front of the car. Full grid is a very, very dense diffusion that passes very little direct light; instead, it becomes a big soft light source all on its own. As the grid cloth relays the light from the sun, and the grid cloth doesn’t move, the light inside the car doesn’t change as long as the sun hits the diffusion.

Thin, light diffusion passes a lot of hard light but creates a soft feeling by radiating some of the light in all directions, turning the diffusion into a source that radiates light into the scene. The diffusion itself becomes a source of light, which creates the softening effect, but the specular light that penetrates through the diffusion casts a hard shadow that will move if the light source moves. In this case I didn’t want to simply soften the light, I wanted to disguise its direction and make it constant.

Heavier diffusion, like full grid, doesn’t pass any direct light. Instead the diffusion glows and becomes the light source, radiating light in all directions–including through the windshield, where I wanted it. The best part, though…

…is that if the sun changes direction the diffusion radiates light in exactly the same way. Outside the car the sun changes but inside the car the lighting stays consistent.

Shadows in the distant background move over time, but if the audience is watching those then we’ve done something horribly wrong. They should be watching the action inside the car, not calculating angles based on shadow length to see if we split shots between morning and afternoon.

We’d planned on shooting this spot in the morning, moving on to another spot in the afternoon. If we’d shot into the afternoon I’d have used shiny boards to keep the diffusion lit as the backgrounds for our shots were on the north and south sides of the car.

Lighting small places, like the inside of a car, is often a puzzle. The grid cloth diffusion radiated beautiful soft light through the front windshield, but the talent went a bit too dark on the opposite side. I could have pushed light through the back window but that would have created what I call the “skunk look,” where the actors are lit on both sides of their faces with a dark line of shadow that falls in the center. That works for dramatic pieces but not for a comedy spot shot in a car. Instead we blocked the rear window with duvetine and put Lee 216 over the rear side windows. I then used a shiny board to push light through the diffusion to add a little fill. Lighting through the rear side windows, instead of the back rear window, put the fill light closer to the lens axis, which always makes people look good.

The biggest hassle was the window glass itself. Most cars and buildings are constructed with “Low-E” glass that’s meant to block both infrared and ultraviolet. What happens when you start with broad spectrum sunlight and shave a little bit off the red and blue ends of the spectrum? You leave behind a lot of green, and that’s what all the windshields in the car did: they blocked some blue and red light and passed a lot of green.

I couldn’t just white balance that away. White balancing to a green interior meant rendering the interior neutral but turning the outside magenta, since removing the green cast from inside the car would remove green from the normal daylight outside the car, turning it magenta. (There is no part of the visible spectrum that is actually magenta in color, by the way. Magenta is always caused by an absence of green. Magenta exists as a subtractive primary color, so you can print and paint magenta, but there is no wavelength of light that is magenta.)

The solution was to put minus green gel on all the windows, to hold back enough green to balance it with lesser amounts of red and blue passed by the Low-E glass. Filters only subtract light–they never add it–so in order to rebalance light that had too much green in it I had to subtract green to bring it back into line with the reduced red and blue.

Imagine the spectrum of light as a line, with red and blue at the ends and green in the middle. Subtracting red and blue pushes the ends of the line downward, leaving a big bump in the middle where green is. Adding minus green gel shaves off that bump so that the spectrum is balanced again.

I think we used 1/4 minus green on the front windshield and all the side windows.

Last but not least, I wanted to bring the highlights down a little as they were toasty even for “Princess Alexa.” I had the grip crew rig a 12’x12′ double net between the car and the background, and we moved it from side to side depending on who we were shooting. Shooting through the net reduced background highlights by a stop and also softened the background a little. When the sun came around, though, it lit up the net and lifted the shadows, making them a little milky, but I didn’t find that to be artistically fatal. In a way it made the background feel a bit more distant as distant objects–a mountain range, for example–often lose contrast due to atmospheric haze.

I’m a little bit of a joke in the San Francisco Bay Area as I almost always get an Arri Alexa package with 30-year-old Zeiss Super Speed lenses. Most often this is to offset the difference in the rental cost between this camera and, say, an Epic, which is a decent camera but doesn’t have the highlight latitude that an Alexa does unless you record HDR, and we didn’t have the post budget for that. Given the choice between a camera that has extraordinary dynamic range and beautiful color or really, really sharp contrasty lenses I’ll go for the camera every time.

I know I used IRND filters, and I’m fairly sure both of these angles were shot with a 50mm lens.

I once knew a cinematographer who literally wouldn’t order a 50mm lens. “It’s normal perspective,” he’d say, “and why do I want that? It’s boring!” For a while I bought into that idea, that “normal” perspective makes for dull imagery, but over time I learned that’s complete crap. Lens focal length is not the deciding factor in making a beautiful image, it’s the arrangement of objects within the frame in conjunction with focal length that makes all the difference. I do believe that people generally prefer to see an abstract view of reality rather than reality itself, which is why wide angle and telephoto lenses are so popular, but there’s nothing wrong with a 50mm lens. It has personality as well, and sometimes it’s the perfect lens for the job. It certainly was for this spot as we used nothing else. I’m quite happy with the composition, and I don’t think the lack of a dramatic camera angle harms this spot in the least. I’m quite happy with how the actors line up in the frame, particularly for the final shot.

Last but not least, I shot this in Rec 709 WYSIWYG mode. There’s a little bit of touchup done in Magic Bullet Looks 2, but this image is 80% of what I shot that day.

You’ll probably see this spot on the web before too long, along with five other related spots. I’ll write up another one of those other spots next month.

About the Author

Director of photography Art Adams knew he wanted to look through cameras for a living at the age of 12. After spending his teenage years shooting short films on 8mm film he ventured to Los Angeles where he earned a degree in film production and then worked on feature films, TV series, commercials and music videos as a camera assistant, operator, and DP.

Art now lives in his native San Francisco Bay Area where he shoots commercials, visual effects, virals, web banners, mobile, interactive and special venue projects. He is a regular consultant to, and trainer for, DSC Labs, and has periodically consulted for Sony, Arri, Element Labs, PRG, Aastro and Cineo Lighting. His writing has appeared in HD Video Pro, American Cinematographer, Australian Cinematographer, Camera Operator Magazine and ProVideo Coalition. He is a current member of SMPTE and the International Cinematographers Guild, and a past active member of the SOC.

Art Adams
Director of Photography
www.artadamsdp.com
Twitter: @artadams

Art Adams
Director of Photography
http://www.artadamsdp.com
Twitter: @artadams