THE SMA FORUM ARCHIVE
Posted by stevencg, on 2004-12-15 16:08:45
lighting questions about doug henedersons work
Hey, does anyone know what doug was talking about here "Thanks also for the comments on the lighting. It's really very simple. Two Arri 500w fresnels on either side, shining through the windows, which have blue gels on the outside, then two 100w bulbs in domed work lights with black wrap cones bent into oblong shapes on either side of the camera to simulate indoor lighting." What does he mean by oblong cones? Also what are gels for?
Posted by Nick H, on 2004-12-15 23:09:18
I don't know the image he is referring to, but I think I get the idea:
Gels are transparent sheets of acetate in different colours, attached in front of lights so they put out, well, coloured light.
Black wrap is heavy aluminium foil painted matte black, it can be bent and shaped, and is used to block the light so it only goes where you want it to. The matte black colour avoids light reflections.
The blue coloured 500 watt lights were giving the effect of daylight, by changing the colour temperature to the bluer tones of daylight. There is a shade of blue called Colour Temperature Blue or CTB made exactly for this purpose. This light was aimed so it comes into the interior set through the windows, like a shaft of daylight coming in.
The domed work lights would be a warmer, yellower colour like normal indoor tungsten lighting. The black wrap would extend the lamp shade, restricting the light thrown onto the set to a smaller area, like the light coming from a ceiling light with a lampshade around it. Sometimes it shines on the floor and the lower part of the walls, but there is a soft edge where the shade cuts it off so it doesn't go all the way up the walls. The work light isn't seen in the shot, just the light it throws, but because it is too big in scale it would cover too large an area if it weren't restricted by the black wrap.
Posted by stevencg, on 2004-12-16 08:34:00
so can i use the CTB gels with only tungsten light or can i use then with incadesent light as well?
Posted by Nick H, on 2004-12-16 19:46:55
It's all relative, depends on the white balance of your video or the filmstock - daylight or tungsten balanced - if you're shooting on film. If you use daylight film stock indoors with tungsten lighting everything will look orange, so you use a blue filter on the camera to correct it. Or you could use CTB gels on your lights, to do the same thing. There's 1/4 blue, 1/2 blue, full blue, and double blue CTB gel, and you can stack several layers as well, it's a question of how blue you want the light to look.
Maybe, if it's Kodak 7248 tungsten film or your video white balance is set for indoors, the light will look white on your camera without any gelling. If so, you might need CTO, Colour Temperature Orange, to make the indoor lights look warmer.
There are also all kinds of colours, green, purple, magenta, whatever. I use a stronger blue for moonlight, or a salmon or CTO for sunset. I used both in My Left Foot, the main light was meant to be moonlight, but there as an amber glow coming in low from the horizon as if the sun hadn't quite set yet. It helped to pick out my character from the background, putting a little warm backlight on him. There's no rule, just play with it until you like the effect.
I think - Jim A or somebody correct me if I'm wrong - that "tungsten" is used as a general term for movie lighting and can include incandescent. (Not flouro, which is greenish.) It's not all the same colour temperature, though, and ordinary domestic desk lamp globes are warmer than most halogens or movie lights. The higher the colour temperature is in degrees Kelvin, the more blue-white it is.
Posted by Boy Oyng, on 2004-12-17 11:45:46
A quick, incomplete primer:
An incandescent light refers to any lamp that contains a continuous filament. The filament glows when electricity is applied. The filament is typically made out of the metal tungsten.
In motion picture work, light is generated in four basic ways:
The first is nuclear fusion. We call that sunlight.
The second is via a filament with electricity running through it. A problem with incandescent lamps is that the filaments deteriorate over time. So sometimes the filaments are sealed in a chamber containing a gas that slows down the deterioration. Examples of that are halogen lamps. But the filament in a halogen lamp is still basically tungsten.
The third is via an electrical spark arcing across a gap between two electrodes. The brightest lights used in movie production (and car lot promotions) employ this method of generating light. So do lights called HMI lights and some xenon lights. And so do really big movie projectors.
The fourth kind of light is the fluorescent. It lights when a gas contained in the lamp has electricity applied to it, which ends up causing the coating of the lamp tube to glow (super simplified explanation).
OK, I said four basic ways, but just recently someone has come out with light panels made of LEDs to be used in movie work, and of course there are lasers and other ways of making light.
Each of these forms of light come with special considerations, such as the color of the light as recorded by film or video, the noises that the light fixture makes, the rate at which the form of light flickers, the heat generated by the fixture, cost, etc.
Lights and lighting accessories in motion picture work sometimes get their names from the way that light is generated, sometimes from the way the light is "controlled," sometimes by the size of the fixture or wattage of the lamp, sometimes by the manufacturer's name, sometimes arbitrarily. For example, an "Arri 500W fresnel" is a light manufactured by the Arriflex corporation, with a 500 Watt incandescent lamp in it, the light of which is controlled (in part) by a kind of lens known as a fresnel lens (named after the guy who invented it).
Posted by Jim Aupperle, on 2004-12-17 13:20:20
I'd say that Boy Oyng's "quick, incomplete primer" coves the basics pretty well. I'll just add the following quote to explain why tungsten-halogen lamps are usually used for stop motion work. I've had to exchange out tungsten-halogen lamps many times in the middle of shots and recall only one example of the light changing enough to be noticed (and we caught that intensity shift on the frame grabber and were able to correct).
"The modern era in lighting began in the late 1960s when tungsten-halogen lamps with quartz envelopes came into wide use. The halogen compound is included inside the envelope, and its purpose is to combine with the tungsten evaporated from the hot filament. This forms a compound that is electrically attracted back to the tungsten filament. It thus prevents the evaporated tungsten from condensing on the envelope and darkening it, an effect that reduces the light output of ordinary gas-filled tungsten lamps. The return of the tungsten to the filament means that the incandescent lamp can be run with a long life at a higher filament temperature and, more important, remain at precisely the same colour temperature."