For clarity, Lumen = LUX/m2. So if you do not have an image on the screen with an area of 1m2 and, for example, 5m2, lux number multiply times 5
If you have a light meter.
Place the projector in such a distance from the screen to get the image on the surface of 1m2, the easiest way, the image must have a 1.28 m wide and 0.8 m high = 1.024m2 now measure the value LUX, and already have LUMEN.
You can not to measure lumens, the screen 100 ", because square meters is constant, and is equal to 1m2 image can not be larger or smaller than 1m2.
if you will measure the value of LUX, the screen 100 ", then you need to calculate how many m2 is the image, knowing the value you multiply by the number of lux m2.
lumen = (.....) LUX x (....) m2
It is an important measure of light, teeth gave important value in LUX.
Important is the image size, and it has to have 1m2 (square meter)It will be in inches (1m2 = 1550in2)
dimension of the image on the screen.
L = 50inch
H = 31inch
As someone has a light meter profesional, let LUX face value, I tend via Galaxy S2, but only in the evening, it is now too bright for measurement.
Measure image with these settings, which you use in everyday life, you do not have to explain why? white image, each of the colors has a different value LUMEN is the brightest green, darkest blue, I invite you browse specifications, RGB LED's Phlat Light.
It seems to me that in PA70G not used LED possibilities, possible that gave that to get more light, but it requires large heat sinks and high current. I was led PhlatLight white, and it up, may be charged 13.5 Ampera shock. typically, however, worked with 9 amps.Mining more light, was associated to a reduction of the life of LEDs.