Lamp luminance

Nitin Sagar · December 9, 2004

hi,

are there any standards for lamp luminance(in lamberts) for screen projector :)

David Mullen ASC · December 9, 2004

SMPTE standard is 5600K at 16 footlamberts, plus or minus 2 footlamberts -- although I heard a rumor that in Europe the standard is a little lower, which is why prints from the U.S. can sometimes look darker in European theaters.

Rob Belics · December 9, 2004

Go to Kodak's site and search for our own John Pytlak to find articles about this.

Dominic Case · December 9, 2004

The SMPTE standard (196M) is for 16 ftLamberts (as David says) but the tolrance is a little looser - screen centre can vary between 12 ftL and 22 ftL, with edges not less than 75% of the centre reading (and in no case less than 10 ftL).

The +/- 2 ftL is for review rooms, where you obviously want to know you have a reliable standard. Realistically, out in the real world of commercial cinemas, there is more variation, with many reports both of theatres running at 5 or 6 ftL (but less on Tuesday afternoons when the audience doesn't warrant so much power consumption), and of projectionists who insist on turning the wick up to maximum, often giving 30 to 40 ftL.

There used to be a British standard of 14 ftL, (in the scheme of things, pretty close to 16) - not sure what its status is now.

Readings are made with a purpose-built spotmeter: (it's about luminance, i.e. reflected light, so the reflectivity of the screen comes into account). You can't rely on your normal cinematographic spotmeter to give you a reliable reading, as it may not respond correctly to the 48 or 72 Hz intermittent natureof the light.

Nitin Sagar · December 10, 2004

The SMPTE standard (196M) is for 16 ftLamberts (as David says) but the tolrance is a little looser - screen centre can vary between 12 ftL and 22 ftL, with edges not less than 75% of the centre reading (and in no case less than 10 ftL).

well out here in india the centre measure's at most 7-8 ft lm and the sides about 5.and i'm talking about the previe screen of the most widely used lab.

how does one compansate for this while shooting?

Dominic Case · December 13, 2004

how does one compansate for this while shooting?

As long as you fully expose the negative, there isn't much else to do. 8 ftL is half the brightness of 16 ftL, but if that's what the lab's preview room runs at, then the print will be graded to suit that, and therefore will be optimised for commercial screens as well.

The darker screen will result in slightly less contrast and colour saturation than you would get with a print balanced for a 16 ftL screen (it's about 4-5 printer points different). An under-exposed neg would make that worse, but over-exposing won't get you much more contrast. So, just keep on the fully-exposed side (as you would anyway).