On 2011-05-23 23:34, Josh Koffman wrote: > On Mon, May 23, 2011 at 10:04 PM, William "Chops" Westfield > wrote: >> (You might wonder that it never caught on to project film onto >> billboards, even though that size of image was pretty "standard" >> technology.) > Well, it would require a projectionist's constant attention. A > standard 1000 feet 35mm reel is about 11 minutes long. Most movies are > distributed on double reels which are 2000 feet, or about 22 minutes > long. I think he meant to ask, why haven't 35mm slides been projected on=20 outdoor billboards for some time now? I think the answer is supposed to be: Because it's hard to compete with=20 some 1000 watts/m^2 (i.e. 100k lumens/m^2) irradiance of the sun with=20 any kind of reasonable projector. Average billboard size might be 25 to 65 square meters. Do they make=20 100kW projector bulbs? > More interesting would have been large format projectors such as those > made by Pani (http://www.pani.com/produkte/projektion/e_projektion.html?e= nglish) > and Pigi (http://www.pigi.co.uk/ETC/Products/products.html). I do > wonder why those never caught on as billboards. Probably bulb cost I'd > imagine. > That Pani page lists a projector with a HMI lamp with 12kW power=20 consumption. At 90 lumens/watt average luminous efficacy for HMI=20 discharge lamp, that's between 43k and 16k lumens/m^2. (16% to 43% of=20 the intensity of the full sun on a billboard). > Josh Joe K --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .