What They Say
Last week I wrote about a PLF cinema facility in Italy that was upgrading to 100,000 lumens with an extra laser light source to show the new Avatar movie (Arcadia Cinema: 100.000 Lumens in PLF ENERGIA Screen). I had some comments from Pete Putman, who knows much more about this than me and he said:
There is a point of diminishing returns with cinema brightness and that is at 50 ft-L, or about 171 nits. At that point, the room is lit up and contrast ratios go to hell. (that’s the knee in the contrast vs brightness curve that I talked of, but it’s good to have some numbers!)
A 55 ft x 30 ft screen (about 1.85:1) with 100,000 lumens on it returns 50 ft-L. 3D glasses would cut that in half to 25 ft-L, which is still pretty bright (SMPTE standard is 16 ft-L with no glasses).
I guess it depends on the screen size, but 55′ x 30′ is pretty large for any cinema and it’s likely screens would be smaller, like 40′ x 22′, which would return over 113 ft-L. 50% of that is still too bright.
Ultimately, 3D may be best delivered to the eye via active eyewear, where the luminance can be tailored to the individual.
What We Think
The screen in Italy was 30 metres wide, which is very wide – 98′ wide, when Pete suggests that 55′ is ‘pretty large’. I checked out the Arcadia screen and it is 16m high (52′ 6″). By my calculations, the Italian screen is 3.11 times bigger, so the 50 ft-L would be reduced to 16.03 ft-L – with no glasses – which happily matches the SMPTE recommendation! However, it would be down to 8 ft-L in 3D assuming the 50% polarisation loss that Pete suggests (although as he pointed out, it is probably higher). (BR)
