To aid in my understanding of Lux and Lumens I threw this together...

I thought someone may find it useful...

http://insomnyak.centelia.net/lumen_calc.htm

pretty cool i like it . Mine came out to 439 lumens i think that sounds about right. May i ask whyat goes into calculating lumens?

Well, first you need a lux meter to read the 9 equal areas of the projected image. Mind telling us how you got 439?

Oh i see how it works now i just plugged in my one reading not all 9 ok ill try it agian.

Ah...no, you add all 9 readings then divide the total by 9. This is your average, then multiply by the sq/mtrs of your projection and not the screen itself.

Gday,

439 would be considered quite high. Even some of the extreme members on this board with 1000W lamps can't manage that. A 'good' reading is probably considered to be in the range of 100-200.

As SIMUL8R has suggest below, use your Lux meter to measure the 9 equal squares of your ANSI Lumen test image (there is one within PGEN which has the 9 circles), enter these numbers into the corresponding boxes within the calculator, enter your height and width of your screen in inches and viola, your lux reading.

The calculator works by taking the average of the 9 readings, multiplying by 0.000645 (the number of square meters in a square inch) then multiplying by the height and the width. This gives you your Lumen output. (Thanks to SIMUL8R for supplying this information initially )

Thanks, mate.

Very handy. I'll be firing up in a couple of weeks, all being well, so I'll give your calculator a whirl too

When I plug everything in and click "Calc" it does nothing. Any help?

Hmm, do you have javascript enabled? What browser are you using? I've only tested it in IE6 and FF3.

Do you get a little yellow icon in the bottom left hand corner when you click 'calculate'?

yaK

439? Wow! I know that it's possible, since I managed a bit more than that myself. I currently get 244, though I fudged the screen size numbers, since I don't have the LxW measurements on hand, I just did a rough 4:3 calculation based on my known screen size.

The only thing that I'd change with this is maybe allow it to take the diagonal screen measurement, and choose an aspect ratio, 5:4, 4:3, 15:9, 16:10, or 16:9 Many of us know these numbers ourselves a bit better.

Meh, I shoudn't have, but here's the math to use diagonal measures...

Area calculation in meters is:

• 5:4 Each inch of diagonal measure gives 0.780869 inches width and 0.624695 inches of height.
• 4:3 Each inch of diagonal measure gives 0.800000 inches width and 0.600000 inches of height.
• 15:9 Each inch of diagonal measure gives 0.857493 inches width and 0.514496 inches of height.
• 16:10 Each inch of diagonal measure gives 0.847998 inches width and 0.529999 inches of height.
• 16:9 Each inch of diagonal measure gives 0.871575 inches width and 0.490261 inches of height.

You can also set a "constant" using the radio buttons, and multiply that, say for the 4:3 ('cause it's the easiest to do in my head) the area (in square inches) = x*x*0.48 where x is the diagonal measure. Other aspect ratios follow the same pattern where the constant (0.48 in this case) is replaced by the factor of the length and width per diagonal inch.

From this, it is possible to determine screen area (in square inches) given the diagonal measure and the aspect ratio. Divide by 1550 in order to get area in square meters. (Well, or multiply by 0.00064516, which seems to be what you're doing.)

Just a thought...