Realistically simulating ambient daylight when lighting video and still photography:
When lighting a scene, a commonly desired effect is to create a natural-seeming ambient light source through a window. It's eminently achievable, but sadly it's more difficult that the usual tactic of plunk down a large HMI outside a window and put a 4x diffusion frame in front of it right at the window. That's a great source, eminently practical, but it doesn't really feel all that natural. From the way the shadows spread out in a v-shape and from the rapid falloff of intensity (remember the inverse-square law!), it's obvious that the light source is close to the window, and it will feel "lit".I am not writing of creating a direct-sunlight effect through a window; that's a different deal. This is about natural-feeling ambient daylight coming through a window, as if you're standing near a north-facing window.
To get a natural feel, think about what daylight is like: it's EVERYWHERE. It's big. It goes all over the place. You're going to need a big source, an not just a flat one. The light needs to come from all directions at least a little bit. One direction will be the brightest, where you're bouncing the unit, but its important that the light come from the full range of directions through the windows. That's what real indirect light does; a bright sky outside your window is bright from all directions.
Make a big box of ultrabounces, griffolyns, beadboard, foamcore, v-flats, or whatever white stuff you have outside the window. Make it as big as is feasible for your shoot. It doesn't have to be as big as the images here, but it does need to be big. Put a large head or two inside the box and bash it into the side, top, or back. If you don't point the light at a part of the box that has a straight-line path to the subject, it will feel even more diffuse, but you'll lose a bunch of intensity.
This is ideal- a 20x12 or 20x20 ultrabounce as the back, a 12x20 ultra overhead, 12x ultras for the sides. If that's not feasible, go a bit smaller- a 12x8 or 8x8 back, 8x sides and roof.
Still effective- two v-flats forming the sides and back with a 4x8 foamcore or beadboard on top.
compromised: a couple of 4x4 beadboards out the window.
Your light will primarily be bouncing off of one spot, but to get that ambient feel, it's still very important to have the other white surfaces surrounding the one that you're hitting with the light.
You may ask, what about hanging some diffusion over the window as well? I generally recommend against that for it to feel natural, because once you have a piece of diffusion right at the window, that diffusion becomes the source and it resets the inverse-square falloff, and once again it will be more apparent that the light source is close to the subject, indicated by flaring shadows and rapid falloff.
Interposing a 4x frame of diffusion between the hot spot of the ounce and the subject can be helpful if you are getting a funny double-shadow effect, where one of the shadows is from the hot spot and the other shadow is from the large general soft source of the box. I do recommend not placing the diffusion right at the window for the reason mentioned above; put it out in the box somewhere, farther from the subject. This double shadow can also be avoided by pointing the light at a spot in the box not directly visible from the subject.
Although this just shows the couch without any people in it, it gives you an idea of the overcast-day through a window feel that you can get with this technique.
yours
Tom Guiney
Gaffer, DP, Bay Area
Inventor and Owner, Airboxlights.com
