# Light entering through back or front of panel?

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#### ELiTeHaYDeN

Has anyone tried having the light come through the back instead of the front of the LCD?

When I first built my LCD projector, I had the LCD up the right way, as i was ill informed, and of coarse it was upside down and back to front but I swear it was brighter...

I had a light meter, I may pull mine out and put the light meter behind it around both ways and see if i get a higher output with the light coming through the correct way...

As I understand the front side has many layers that stop glare and things like that, perhaps its having a negitive effect on the light, like reflecting it.

Oh and my light meter reads in Lux and LC so does anyone know how to first, convert it to Lumen and then measure the projection screen? something about splitting it into a set of squares then measuring each square and adding them all togeither on a full white ouput to get teh value?

at 180" i get 30 lux in the centre and 20lux on teh sides.

#### Guy Grotke

average lumens on the screen

1) Divide the screen area into nine equal-sized rectangles.
2)With a "brightest white" screen image, measure the lux at the center of each of those rectangles.
3)Find the average of those nine readings. (Add them together, then divide by 9.)
4) Measure the screen image vertical & horizontal dimensions, and compute the number of square meters.
5)Multiply the average lux value by the image area in square meters = Average Lumens.

Just for a comparison, 100 lumens is considered the minimum for a cinema.

#### ELiTeHaYDeN

243 lumens would be the result i get.

2.7m x 3.6m = 9.72m3

9.72m3 x 25 lux

lux is the same as lumens isnt it?

this is on a bulb with about 1000hrs on it.

#### Mikey p

ELiTeHaYDeN said:
lux is the same as lumens isnt it?
1 lux equals 1 lumen/square meter

#### Rox

where did you measure 25 lux?

gg told you how to do it, check it.

Can you tell us your setup?

(GG, I think you confused the data by error, it is 100 lux the cinema standard, 100 lumens would be the output on just 1meter square of 100 lux brightness on the screen.)

this makes me think, all the measurments i have heard by know are in the range of 10-50 lux, maybe, we are projecting to large...
anyway, it is the standard but a standar does not mean our WOW factor is worst.

#### ELiTeHaYDeN

if it was 100 lux then the output of the cinema projector would be over 1000 lumens and they arnt that bright.

my lux meter also explicitly says in the manual its most sensitive to the 2000k color temperature range, for standard home lighting.

So i guess that would drop my results, browing can be done with the 150w lamp i have in the room and gaming, most movies are watchable ... dark movies are unwatchable with the lights on tho.

turn the lights off and shes all good.

#### Guy Grotke

oops, my mistake

>it is 100 lux the cinema standard, 100 lumens would be the output on just 1meter square of 100 lux brightness on the screen

Yes, of course Rox is correct. A cinema film projector will light the screen with about 100 LUX of light on every part of the screen. So each square meter of the screen will get hit with 100 LUMENS.

If you can get your DIY projector to put 100 lux on every part of the screen, then you will have a picture as bright as a movie theatre. (Have you noticed what happens to a movie theatre screen image when the house lights go up? You can barely see it!)

#### ELiTeHaYDeN

thats easily obtainable with a smaller image size.

but somethings not right, cause my projection is brighter than a cinema projection when the lights are on, but i aint getting 100 lux per square - of coarse it matters how much light is being put out from the house lights in the cinema, but generally its less than your average room, here in NZ it is anyway, its still relitivily dim

#### Rox

it is not posible you to have brighter image with 30lux max brightness than the cinemas standard 100lux.

mm, what do you mean by 2000K maximun sensityvity? you mean that the luxmeter was calibrated to that color temp from an incandescent lamp? is it?

#### ELiTeHaYDeN

Rox said:
it is not posible you to have brighter image with 30lux max brightness than the cinemas standard 100lux.

mm, what do you mean by 2000K maximun sensityvity? you mean that the luxmeter was calibrated to that color temp from an incandescent lamp? is it?

at 60" picture size its like 90 lux, or higher

and yes its calibrated to icandescent lamps

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