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In Reply to: OT: light meter for HT use? posted by Aroc on April 27, 2004 at 03:58:27:
Photo meters used for measuring light for photographic exposures read out in exposure values (EV numbers), and not direct light units of measure. They are used to measure incident and reflected light.Both a foot-candle and a foot-Lambert are equal to 1 lumen per square foot. The foot-candle measures light that is incident on a surface while a foot-lambert is a measurement of light being radiated from a source. The problem with measuring a foot-Lambert is that the light reading sensor needs to be directly on the surface so that the reading is not affected by light fall off (1/d^2) where "d" is the distance from the source to the meter.
If you could find a Photo Research Lite Mate, or Sekonic L-246 (much cheaper) foot-candle meter you could read the ambient light (foot-candles), and, in theory, approximate a foot-Lambert reading by holding the meter cell without the integrating lumidisc against the CRT screen in the area you want to read.
Follow Ups:
Thanks for the follow-up!Is the 'photo meter' you refer to just another name for a 'light meter' or are they two separate things? Maybe I need a different tool? What tool could I use to measure 'how bright' a CRT TV is vs. my front projection screen? Does the fact that one is direct and one is reflected mean I need two different meters? I have a radio shack 'spl meter' to tell me 'how loud' I listen to music, I'm just looking for the analogous meters for a front projection display.
"Photo meter" is short for photographic light meter. Photographic light meters are used to measure incident or reflected light to calculate the correct exposure. They do not give direct readings in light units (foot-candles).As I said, you might be able to use a foot-candle meter held directly on the screen to give you an approximation of the actual foot-Lamberts. I'm afraid there is no equal in photography to the simple Radio Shack sound level meter.
Foot-candle meters are used in motion picture and video production for setting up lighting so that the light ratios remain within the desired production values. That is why you can find meters that read out in foot-candles.
Measurement instruments that read out in foot-Lamberts are laboratory level test instruments not needed for general photographic uses.
What I can do, is try out my PhotoResearch LiteMate III foot-candle meter with my rear projection Pioneer Elite and see if it appoximates the values given by Pioneer for screen brightness.
What you need is a video photometer. They are available from several sources. Just do a web search for "video photometer" and you will find at least five companies with these instruments.My tests with my foot-candle meter only proved it was not an accurate measurement method.
I know what to look for now. :-)
Aaron
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