Measuring data projector output

[sleah]

A little OT....

 

My boss has asked if we can measure the output of data projectors to determin if they are still outputing a decent brightness? i.e. is a 2000 lumen projector still doing 2000 lumens?

 

I know the eye is the best judge of condition..... but I'd like to give him an educated answer. I normally judge by lamp hours and picture quality and plenty of "does it look OK?".

 

ASFAIK it would be near impossible, especially with a normal photographic type lux meter to get anything meaningful. Or am I missing something?

 

Thanks

Simon

[timsabre]

The lumen figure, as you probably know, is the total output of light from the unit, whereas lux is a measurement of the light level at one particular point.

 

By measuring the total illuminated area, and assuming that the light level is a perfectly even field, you can calculate the lumen output from a lux reading (or get an average from a few readings).

If you google "lux to lumens converter" there are some online calculators that will work it out for you.

 

However, without an equivalent calculation of what the projector did when it was new, this may not be particularly useful as I'm sure there is lots of manufacturer jiggery pokery going on in the specified lumen output figures. They seem to be a bit like car MPG figures.

[Brian]

They seem to be a bit like car MPG figures.

Or even the output of LED lanterns.

[timsabre]

They seem to be a bit like car MPG figures.

Or even the output of LED lanterns.

 

Well they are OK if they actually state the lumen output, you can do some real comparison then. It's the "equivalent to 500W" statements which cause that problem.

[Shez]

I did some before and after lamp change measurements last year; I'll see if I've still got the numbers anywhere. I do recall that the measured brightness varied quite significantly between the centre and edges even though it looked pretty even. The total measured output was also a lot less than the manufacturer's quoted figures.

I used a fairly generic meter which hadn't been calibrated for about four years so was probably more useful for relative measurements than absolutes.

[sleah]

I did some before and after lamp change measurements last year; I'll see if I've still got the numbers anywhere. I do recall that the measured brightness varied quite significantly between the centre and edges even though it looked pretty even. The total measured output was also a lot less than the manufacturer's quoted figures.

I used a fairly generic meter which hadn't been calibrated for about four years so was probably more useful for relative measurements than absolutes.

 

That sounds like a reasonably good idea! Relative would be perfectly acceptable for us, as we have many identical models :)

 

I'd say that the best method would be to hold the meter up against the lens to eliminate ambient light? It would be impossible to recreate the same ambient light levels in every room.

[timsabre]

I'd say that the best method would be to hold the meter up against the lens to eliminate ambient light? It would be impossible to recreate the same ambient light levels in every room.

 

You can just measure at the screen with and then without the projector, then subtract the ambient reading.

I doubt you'd find a lux meter which would give a reading against the lens. Maybe something from a physics lab might.

[Shez]

Have a look here - everything you could ever want to know about measuring projector performance. In short, project a 4 x 4 grid in full white and measure the light level in the centre of each cell. Take the average and subtract the ambient light reading. Plug the answer and the screen dimensions in to a formula and there's your answer.

[AHYoung]

One lumen is 1 lux / m2. therefor in a dark room in theory you measure the light hitting the screen in lux with the projector on full white, divide it by the screen area and that's your lumens. If you were doing this seriously, youd take 9 measurements across the screen and measure them. Theres more to it if this is a scientific reading you want, but too be honest anyone who would consider doing this simply has too much time on their hands. The simple question is is the projector bright enough for the specific task? it either is or it isn't and that's got fek all to do with the claimed luminous flux. If you need to see an image clearly in a specific situation you can or you cant, the numbers mean little.

 

Lumens have allways been very "peak music power" and you could line up a dozen different units with the same specs and they'd all be utterly different brightness. Add to that that some manufacturers claim centre lumens - measured in the centre only , peak lumens - a small white area in a black screen or Colour Lumens - A variation on colour light output whre the rgb values are separately measured as opposed to the more normal ansi lumen and its an utter minefield not helped by manufacturesrd calling units hdsomething k where something is the actual output plus a bit...

 

 

 

 

 

[sleah]

I'd say that the best method would be to hold the meter up against the lens to eliminate ambient light? It would be impossible to recreate the same ambient light levels in every room.

 

You can just measure at the screen with and then without the projector, then subtract the ambient reading.

I doubt you'd find a lux meter which would give a reading against the lens. Maybe something from a physics lab might.

 

DOH! (obviously...)

and

Oh. :huh:

 

The simple question is is the projector bright enough for the specific task? it either is or it isn't and that's got fek all to do with the claimed luminous flux. If you need to see an image clearly in a specific situation you can or you cant, the numbers mean little.

Completely agree!

 

Thanks for all the replies, I now have something meaningful to tell the gaffer. :D

[avdavesound]

but too be honest anyone who would consider doing this simply has too much time on their hands.

 

 

you would be surprised the amount of tests you need for a military flight simulator!