I just got my luxmeter from Hong Kong (the ebay $32 dollar version). I plan on using it to compare the results of my new build to my older build and to tweek my new build. While looking at the measurment sensor I realized that it is just about the same size as the standard LL triplet. It occurred to me that if the luxmeter averages the light across the entire surface of the measurment head then all I would have to do was to stick the sensor up against the triplet (using tape) and take a single measurement. That should give me a foolproof way of determining total output in a single measurement. Even high ambient lighting conditions would not interfere with it.

To calibrate my new projector, I would simply tape the luxmeter to the triplet and move then lenses and lamp around until I get a maximum reading.

For those of you who have the same meter and have already performed an output measurement with the 9 point method, could you try this and let me know if it provides a similar reading. If the theory is correct, then this method should be more precise and accurate than the 9 point method.

The one good thing about a 9 point reading is that it tells you how well the light is distributed across the screen. You're suggested method will not tell you that. May be good for intial lamp & triplet placement, but fresnel placements I find effect the light distribution quite a bit...

cheers,
gs

I use the luxmeter on the outside of the box, up against the lens to make tests. Although you can't use this for final lumen ratings. This is a good way to see if you are gaining or losing from changes. Without having to go all the way to the wall. for instance, I get 17,000 lux at the highest point on my lens. I made the change of taking out the reflector, and could only get out like 10-13,000 (can't remember, but much less) or something. So that told me there was change. Then I checked it when I changed bulbs. It is just alittle more than the 16,500ish with the 875w bulb. At the wall, it was 5 lux different or something close. But it tells you what your change is, just can't tell the total lumens. But it will be helpfull. I use to check on the far side of the lcd, but that meant opening my box and stuff. This is quick and easy.

I agree with that statement fully.

standar lumenlab triplet is somewhere 62mm clear lens diameter... this is 0.003meters square area... @17000 lux should result in somewhere; 51 lumens.

this is under average in my opinion. Please make some 9 test to see if you have a diferent (preferably higher for you) value.

miedosoracing: what is on the lcd when you are measuring this? white screen?

Rox, I have the 135mm at 500mm-550mm focal.

Yes, white screen. Rox is way off though. I have to measure it now since I changed so much. But I believe I am between 250 and 300 lumen now. i was at 350 measured, but I have taken the fresnels from 220mm to 330mm and other changes. So I dropped for sure, but less drop off at the corners. My screen looks very even.

Bye the way. 1000w lamp at 51 lumen would make me give up :-)

I think what Rox was saying was that your single measurement right up against the triplet would have equated to about 51 lumens and that can't be right. I did a quick measurement and got in the vicinity of 35000 lux, give or take. You should have gotten about 100,000 lux or so in your measurment to equate to 350 lumen.

The problem may be that you are using a Pro lens?, or that your single measurment is out of scale.

My original theory was that if this fit the standard triplet then it might make a fool proof way of getting a good total output reading on a single measurement. When I tried it I found that both the luxmeter head and the standard triplet are convex, so it is not a straightforward a measurement as I thought it would be. If I turned the triplet around it might work, though.

Yeah, like I said from the first post here, I don't think this is gonna be a good way to get total lumens. That is for sure way off. I know for a fact I am getting over 200, but still think I am getting around 250-300. Because I had an average of 103 something lux before, at a 3.4m screen. I am sure it is lower by quite a bit because I changed so much, for evenness. But I gained in the outter parts and lost in the middle quite a bit. Even if I get 200, whatever the number is, it is more pleasant to watch with an even screen than a mixed outter and middle screen. But for sure way over what those numbers imply from the lens calculation.

PS, phutton, what bulb are you using etc. Seems weird you get 35000 lux out of the lens.

Keep in mind that the 35000 lux reading does not equate to 35,000 lumens per meter. The light is concentrated to the area of the triplet, so I would multuiply that by 0.003 to get total output. If you are using a diffeent triplet you would have a diffeent multiplication factor. If it is a larger triplet it would explain why your reading was so low (your multiplication factor would be higher).

By the way, I am using the Venture ed28 pulse start lamp and ballast with the cmv 529A lcd (AG still on). I posted what my output was in the lumens thread. If you can, run a 9 point measurement and include your data also.

sorry, I was out of this thread...

miedoso; I thought you had a standar lens, (fitting the luxmeter sensor on the lens got me to that conclusion...) now as you said, your 135 triplet... this is 125mm clear lens aperture diameter and this means; 0.0122meters square area at the triplet. Multiplyed by 17000 (your lux measuremt at triplet = 208 lumens. that is closer to your sugested 250-300 lumens range.

if yo had 275 lumens there, you should meassure 275/0.0122=22400 lux at triplet.

Anyway, the screen measuremnt is better choice in my opinion.