Lux to Lumens ? - Home Theater Forum and Systems - HomeTheaterShack.com

 
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post #1 of 9 Old 03-08-14, 04:23 PM Thread Starter
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Lux to Lumens ?

I just bought a light meter to measure the light output off PJ screen, but it measures in LUX , how can i easily convert to Lumens ?

Thanks
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post #2 of 9 Old 03-08-14, 07:19 PM
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Re: Lux to Lumens ?

Quote:
randyc1 wrote: View Post
I just bought a light meter to measure the light output off PJ screen, but it measures in LUX , how can i easily convert to Lumens ?

Thanks
You could multiply your Lux reading by 0.09290304 or just use this converter. Now multiply the square feet of your screen by the foot-candle value and you have Lumens.

For example: You are getting a reading of 150 Lux with the light meter at your screen and pointing at the PJ. 150 times 0.09290304 = 13.935 fc. Your screen is 120" diagonal 16:9 ratio which equals 59" x 104". Multiply 59 by 104 to get the screen size in square inches which here is 6136. Divide that value by 144 to get the screen size in square feet which here is 42.611111. The lumens hitting the screen would be 13.935 times 42.11111 which equals 586.81831 Lumens.
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post #3 of 9 Old 03-09-14, 04:45 AM
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Re: Lux to Lumens ?

Or, if you are familiar with meters:

Lumens = Lux x s.m. (screen's width x height)
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post #4 of 9 Old 03-09-14, 10:09 AM Thread Starter
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Re: Lux to Lumens ?

Quote:
Harpmaker wrote: View Post
You could multiply your Lux reading by 0.09290304 or just use this converter. Now multiply the square feet of your screen by the foot-candle value and you have Lumens.

For example: You are getting a reading of 150 Lux with the light meter at your screen and pointing at the PJ. 150 times 0.09290304 = 13.935 fc. Your screen is 120" diagonal 16:9 ratio which equals 59" x 104". Multiply 59 by 104 to get the screen size in square inches which here is 6136. Divide that value by 144 to get the screen size in square feet which here is 42.611111. The lumens hitting the screen would be 13.935 times 42.11111 which equals 586.81831 Lumens.
Thanks Harpmaker , i will keep this for reference .

So i put the meter infront of screen facing PJ ,.. what kind of images do i project to see potential light output of PJ ?
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post #5 of 9 Old 03-09-14, 12:45 PM
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Re: Lux to Lumens ?

Quote:
randyc1 wrote: View Post
Thanks Harpmaker , i will keep this for reference .

So i put the meter infront of screen facing PJ ,.. what kind of images do i project to see potential light output of PJ ?
The best image to use is "100 IRE" from a calibration DVD. This is the brightest white signal for video. I forget now if it is the same as a RGB value of 255, 255, 255 or not. I know that "0 IRE" (the darkest black for video) does NOT have a RGB value of 0, 0, 0. Hopefully someone that knows more about this will chime in here.
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post #6 of 9 Old 03-09-14, 01:09 PM
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Re: Lux to Lumens ?

Quote:
Harpmaker wrote: View Post
The best image to use is "100 IRE" from a calibration DVD. This is the brightest white signal for video. I forget now if it is the same as a RGB value of 255, 255, 255 or not. I know that "0 IRE" (the darkest black for video) does NOT have a RGB value of 0, 0, 0. Hopefully someone that knows more about this will chime in here.
Here you go Don...





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post #7 of 9 Old 03-09-14, 02:25 PM
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Re: Lux to Lumens ?

Mech, if we are talking RGB then the white pattern is 255, 255, 255. 235 is the white when encoded in 16-235 levels.
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post #8 of 9 Old 03-09-14, 03:18 PM
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Re: Lux to Lumens ?

A, ok then...i now understand what you say!

I had the impression that Don was referring to pure RGB values and not video levels.
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post #9 of 9 Old 03-09-14, 05:55 PM
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Re: Lux to Lumens ?

Thanks for the help on this Mech and Yiannis. A lot of people get confused about this topic (maximum White and Black levels). People using a "regular" video source like a DVD player have a dedicated video output of 235 RGB for White and 16 for Black, but many that use a PC as a video source have the 255-0 RGB output and have trouble calibrating their projectors.
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