real lumens output meassuremts

Rox

Member
2004-07-25 10:06 pm
?
people talks about 1000-1200 lumens output on their 400W based setups but then there are few ones that have meassured the ANSI lumens on their setups and found a disgusting result.

Guy grotke is a member that most of us have asked things more than once, and i apreciate him much since i learned a lot from him, is one of the brains here... Well, his meassurements show a 52 ansi lumens output on his 250W based diy. IT´s hard to believe he got 52 when the most comon should be 1000lumnes.

The human eye is very tricky, i wouldn´t trust on those that say things as "it looks like 1200 lumens comertial"... The luxmeter is a objetive meassurement tool. But then people says stupiditys such as "there are too much factors on ansi lumens", well,
So why do some say 1000 lumens?

whats the real meassuremts on our setups? 51 poor lumens?
 

pinkmouse

diyAudio Moderator Emeritus
2002-04-03 7:15 pm
Rotherham, England
I have had a wide experience of commercial video projectors ever since the old Barco 300s first came out. From the fact that most of you have to take pictures in blackout conditions, I would guess that your projectors are running at about 50-100 lumen maximum, with the average below this. 1000 lumen should produce a brightly lit 60" image in ordinary room lighting...
 

Rox

Member
2004-07-25 10:06 pm
?
so those that say we can have 1000-1200 are cheating us?

I also think that if we get 300 lumens we can feel very happy.

well, guy grotke looks happy with 52 lumens. :D

the cienema standar is 100 lux (100lumens for each square meter) if we take this onto acount, then 200 lumens output is perfect for 70" diagonal image.

I don´t think someone has 1000 diyprojector lumens.
 
unifromity is the problem with diy projectors... the larger the LCD the bigger the problem is .. the centre is always brighter than the corners, about the only thing you can get close to uniform brightness on is a 7" lilliput or perhaps smaller, anyone who insists on having uniform brightness on a 15" projector i think are kidding themselves.

My projector is very close to a 1500 lumen commercial projector with the lights on(100w bulb 1 metre away from the screen) in the centre only ( i have actaully compared ) - as you get to the extreme's however i'd say its no better than a few hundred lumens.

People on the forum are taking pics with the lights on but 9/10 its not direct light on the sceen.

What im going to do now is create a new thread dedicated to rating peoples output, with the lights on and how much gamma they need etc.
 
I did not state I had 1500, I said it appears to be very close, because a friend has a 1500 lumen commercial projector, so its easy to make a comparison.

But as stated above, the eye is very deceptive, i doubt it is 1500 lumen or anything close, but it appears to be very similer in brightness to the 1500 lumen projector, around the centre area only however.
 

Jl2

Member
2005-03-17 8:10 pm
Rome
My personal point of view:

Despite technical data and engineering considerations, the main point is to view a good movie with lots of good friends and a bowl of pop corn, having a product you just built with your own hands and performs ALMOST like a commercial one.

Human nature are not numbers! ;)
 

nick[x1]

Member
2004-09-27 11:26 am
Home
My personal point of view:

Despite technical data and engineering considerations, the main point is to view a good movie with lots of good friends and a bowl of pop corn, having a product you just built with your own hands and performs ALMOST like a commercial one.

Human nature are not numbers!

although i agree with that, as long as it projects a image who cares but some people prefer to know the technical data of there master peice :p


Dont the comercial projectors lcd eat less light than one from a diy?
 
about the only thing you can get close to uniform brightness on is a 7" lilliput or perhaps smaller, anyone who insists on having uniform brightness on a 15" projector i think are kidding themselves.

I use-to think the same thing. I think the key to getting uniform lighting is all in the pre-condenser, not the actual size of the LCD. There was a thread on diybuildergroup recently where Guy suggested using a 550mm FL rear fresnel to improve dim corners. If it were used with out a pre-condenser then it would improve the dim corners at the expense of light output. Basically using a 550mmFLfresnel on a 15” LCD is just a scaled up version of a 7” LCD with a 330mm FL fresnel. When I did a rough raytrace of this dim corners were not improved.
Here is a copy of my post at diybuildergroup.
I've done some rough ray traces with a 220mmFL fresnel, a 550mm fresnel and a 550mm FL fresnel with a pre-condenser. When the pre-condenser is added the light distribution changes back to the same as a plain 220mm FL fresnel. So it appears as though there is no advantage in using a set up like this. The only thing that I suspect could improve dim corners is the spherical aberration introduced by the pre-condenser. So we'll have to wait until Guy finds some time to do a test or perhaps if I get my projector up and running and make a simple LDR meter, to find out if it improves.

DJ.
 

Attachments

  • intensity.jpg
    intensity.jpg
    30.9 KB · Views: 273
Tell Guy grotke that he should use 550 rear at the expense of light

I think Guy already understands this.
My Point is that dim corners that are a result of the inverse square law will affect ALL LCD sizes the same. An example would be to take a 7” LCD and matching a fresnel with the lamp at 1 meter away. The resulting image light uniformity would be very good but it would be dim. Now if we place a plain spherical pre-condenser close to the lamp, so that more light can be collected and it was ABERRATION FREE, then it would be no better in terms of dim corners than a 17”lcd with the lamp at 220mm. The key to better light uniformity is in the pre-condenser’s aberration or in the reflector’s aberrations. If we could get an anti-aspherically corrected pre-condenser, if these existed, then they should improve dim corners.
I’ve heard Trev talk about using an all parallel light engine but I’m unsure how he is intending to implement it or whether it will be effected in the same way, hint hint.:D ;)

DJ
 

Rox

Member
2004-07-25 10:06 pm
?
yes, i know he understands this, but maybe it is not the ligh uniformity the most important thing to solve. If he had more lumens, maybe it is a good busines to losse some lumens vs achieving better huniformity, but would say it is not his case.

he says things such as upgrading to 400W, so i believe it is the brightness the main problem.
 
As i understood it, the main reason one cannot acheive a uniform lit LCD(15") with a 220mm was because as the light reaches the corners it is approaching critical angle/ the angle of which light is reflected... So alot of the light is being reflected by the fresnell, if you replace the 220mm with a 330mm fresnell and matching longer focal condensor this will be alot better at the exspense of a little bit of brightness(this is reduced if you use the right condensor)

Reducing the LCD size has the same effect as using a longer focal fresnell.

So.. i think the best solution is to find some way of lighting the lcd without the fresnell, eg, a eliptical reflector, but once again, the angle of the light hitting the corners is going to be the same as it was hitting the fresnell.. and perhaps even dimmer because the LCD is more reflective...

If this is the case then theres only one way to get a uniform image! - smaller LCD.

Example.
 

Attachments

  • untitled.jpg
    untitled.jpg
    45 KB · Views: 223
Rox said:
yes, i know he understands this, but maybe it is not the ligh uniformity the most important thing to solve. If he had more lumens, maybe it is a good busines to losse some lumens vs achieving better huniformity, but would say it is not his case.

he says things such as upgrading to 400W, so i believe it is the brightness the main problem.

well for me, I am 100% happy with the brightness in the centre and am willing to trade brightness for uniformity.. for example a reduction in brightness in the centre, but more uniform.
 

Rox

Member
2004-07-25 10:06 pm
?
that's the idea, yes.

But remenber that introducing a pre-condensor lens, will virtually icrease the arc lenght on the bulb and this is also negative. Could be that the arc lengh is so big that the light is not entering the projection lens, also the light will be more difficult to manage. So let´s study every case slowly before doing anything.