Practical lights are light sources that are visible in the shot. They can have a variety of purposes like adding depth or to justify that the light in the scene is coming from this light sources. On this page i will focus on the latter and will cover the former on the page about ‘depth’.
In a lot of cases practical lights aren’t the main light source like in the shots posted below. If you pay close attention to the visible light sources you will notice that non of them have a significant impact on the illumination from actors and set. Removing them from the shot wouldn’t alter the overall light to much.
Why aren’t practical lights used to illuminate the shot?
There are a couple of reason, which not all apply to all them.
- Limited usage for artistic lighting. The desired lighting for actors/set and framing of actor/set/practical lights can’t be achieved.
- exposure: in a shot like Blade Runner maintaining the correct exposure throughout the frame would be very hard. Most likely either the candles would be exposed correctly and the actor/set would be in complete darkness or the actors/set are fine but the lamp would blow out and cause a lot of unpleasant lens flares. If the camera is even able to get the desired exposure for a wall that’s 5-10m(~15-30feet) away.
- size and/or intensity of the light source. e.g. the candles in shot from Revolutionary Road are by far not bright enough to get that much light on actors and the set. For comparison that a look further down to the shot from Barry Lyndon.
- Lens flares: Undesired lens flares. In general the brighter the light source the more likely lens flares will be visible.
Yes there a shots like in Stanley Kubrick’s Barry Lyndon, by Cinematographer John Alcott, that used candles as the only light source but its rather rare. To get enough light into the camera they use a Carl Zeiss Planar 50mm f0.7(resulting in very shallow depth of field) and push-developed the ISO 100 film by 1 stop. Shooting digital these days reduces a lot of this technical limitations. Modern camera allow for high ISO with reasonable grain levels and a large dynamic range from up to almost 14 stops. The artistic limitation remains though.
Practical light in CG:
In cg most of the time we aren’t limited to the power or size of the light source and can turn on/off lens flares when ever we want its still recommended using practicals the way a cinematographer would use them to enhancing the story and believability. This will add a lot more flexibility and also increases the overall quality of the lighting. Using this ‘practical lights on set’ workflow in cg lighting has also one huge technical advantage – a lot less render artifacts. The brighter the light source and the closer to an object over even worse inside an object the more noise will occur in the from of fireflies and other artifacts which leads to increased render time trying to solve the noise.