Optimizing Light Source Shape

discussion about metal halide, ballast, capcitor ignitor,reflector, condenser lens
Schmit01
Advanced Member
Schmit01
Advanced Member
Joined: 22 Jan 2013, 00:38

01 Jan 2017, 23:12 #51

So I have been doing a bit of experimenting with light tunnels used in DLP projectors.

By having a light source converge into a rectangular mirror tunnel matching the aspect ratio of the LCD you are have you can achieve 90% or more light capture with near 100% light distribution.
I actually found a patent on it when doing research.
https://www.google.com/patents/US5902033



When the light exits the tunnel it creates a number of duplicate rectangular projections which scatter. By placing a lens after the light tunnel, it overlaps all the rectangular projections over each other, exactly the same way fly eye lenses work in LCD projectors. By placing two lenses after the light tunnel with short focus lengths you can reduce the amount light deflecting out away from the tunnel and creating a smaller emitting area while having better control of the projection size.

There are a few issues.

1. Long focus points. based on my experiments you looking at minimum 500/600mm fresnel for the back, so folding mirrors will have to be used. This can be countered by using a larger or shorter light tunnel but mean larger lenses and larger emitting area. However the benefit of a longer focus point is less deviation of the light meaning better detail. 4K anyone?

2. The smaller the light tunnel the more heat. Front surface mirrors are only about 97/98% efficient, meaning a small amount of light is absorbed. Any where from 15000 to 20000 lumens and you looking at 1 watt. Not much but can become a lot the more when it bounces multiple times within the light tunnel.

3. Getting the light into the tunnel. Getting a 15x15mm 128W LED array into a 10x6.25mm light pipe (1.6 aspect ratio) can be tricky. By projecting the LED onto a round Fresnel, then using a number of smaller fresnels like a fly eye lens to break the light into smaller pieces. You then have a second fresnel focus all those smaller fresnels over each other onto a point getting down to a 5mm focus point. The more smaller fresnel/lenses the smaller the emitting area.

The alternative is to use an array of smaller LED's like the Cree XHP70 rated at 4000 lumens. With a 7mm emitting area this would be perfect.

4. Light pipe size. The average sizes I have found online are about 5mm wide internally which is what I've been experimenting with. I'm looking for a about 10x6.25mm +-. so when the holidays are over I'm going to try get a front surface mirror water jet cut to my required sizes. The finish and if they can cut the small sizes are my concern.

I looked at making a tapered light tunnel, the issue I encounted was as the tunnel got smaller the light interacted more with the joints between the mirrors when bouncing more between the horizontal and vertical mirrors causing more light loss into the mirror and defects in the light. But will try again with the water jet cutting.

Im awaiting some new fresnels and short focus lenses and will post a test rig Im building. Struggling to get anything larger that 6" with a 600mm fresnel, but hoping the short focus lenses will get that up to 10".

Cheers
Ryan



email rsschmit@gmail.com
Reply
Like

Schmit01
Advanced Member
Schmit01
Advanced Member
Joined: 22 Jan 2013, 00:38

22 Mar 2017, 21:33 #52

So my new lenses finally arrive. Thought I would show you some of the results.
I created some test light tunnels using aluminium sheet before having the mirror water cut.

In the end I settled on a 13x22mm by 35mm long tunnel due to the 10x7 chip LED I have. I worked out with a 600mm Fresnel I could achieve the same focus as a 7x7 chip with a 10" panel.








The light output is not perfect due to the aluminium having a bit of a radius at the corners and I couldn't hold the primary focus lens and my phone at the same time so apologies, but I can achieve a nice 5/7mm perimeter around the LCD area giving me around 75% to 85%.

My box will be a bit big but I'm willing to sacrifice size for even light output and great focus & detail.

All I have to do is have the FS mirror water cut and order the 600mm Fresnel now that I know that's the rough distance I need. And hope everything still works with that combination.

Ryan

email rsschmit@gmail.com
Reply
Like

bevo77
Advanced Member
bevo77
Advanced Member
Joined: 29 Oct 2011, 16:49

28 Mar 2017, 21:15 #53

looks great. So is your optical setup?

LED

Condenser (Diameter, ? FL)

Light Tunnel (13 x 22 x 35)

Collimating Fresnel (600mm)

LCD

Condensing Fresnel (220-240mm)

Triplet


Also, what are your distances between? is the light tunnel just bent aluminum?
Reply
Like

Schmit01
Advanced Member
Schmit01
Advanced Member
Joined: 22 Jan 2013, 00:38

28 Mar 2017, 22:36 #54

Hey Charlie

The image below should help.




The first condenser lens I have is 28mm but is too big so have some 19/20mm lenses coming.

For my testing, yes just bent aluminium sheet, I'm also testing using a 20mm pipe and shaping the end to be rectangular like I originally started in this thread. I will then try use stainless steel and polish it to a mirror Finnish.

The advantage is round lens captures all the light at the round entrance then tunnel converts it to rectangular.

I'm still going to get the mirror water cut, just need to find the time to take it there.

Ryan
email rsschmit@gmail.com
Reply
Like

bevo77
Advanced Member
bevo77
Advanced Member
Joined: 29 Oct 2011, 16:49

29 Mar 2017, 04:13 #55

From your drawing, you will place the 600mm fresnel about 20mm from the LCD and then the condensing Fresnel and triplet? Have you decided whether to put the FS mirror before or after the triplet? What size of FS mirror do you need? I have a couple that are trapezoidal and about 11 in wide on the longer base and 8 inches across the top.

I'll take a look at my stock of fresnels as I have some long FL lenses left over from the Lumenlab days when we were using 15 & 17 inch panels. [I still have some of the metal halide lamps and ballasts!]

I take it that you will use the standard size LED chip 40 x 40 and not attempt any of the smaller chip LED like bumhee used on his 4K projector? I like the light output and they have a built in thermistor that connects to an electronic thermometer. Using a VGA cooler, I can run the fan whisper quiet and it keeps really cool.

Did you ever strip your 4k panel?
Reply
Like

Schmit01
Advanced Member
Schmit01
Advanced Member
Joined: 22 Jan 2013, 00:38

29 Mar 2017, 06:57 #56

Yes you correct, 600mm fresnel/LCD/220mm Freslnel 210/240mm Lens.
I will be using 2 front surface mirrors for the rear Fresnel and a straight design fro the front.

I have plenty of mirrors in stock thanks. The first one will be 200x85mm and the second is 100x85mm.

This is the concept I working on at the moment. Two level box 250mm high with water cooling below with sound absorbing panels. Also intake and discharge at the front like the Epson power light series. I want this to be extremely quiet. Also I have zero chance of light leakage.



Yes I will be using the 40x40 chip. The main thing driving this is brightness issues with the Topfoison screen. I need to effectively get a minimum 15000lm through the LCD for my 100" screen while keeping detail.

I did not buy the 4K panel. I want to stick to a sub 6" screen.
email rsschmit@gmail.com
Reply
Like

Schmit01
Advanced Member
Schmit01
Advanced Member
Joined: 22 Jan 2013, 00:38

07 Apr 2017, 06:05 #57

So I was playing with the polarizing beam slitter (PBS) I have, I always thought the light had to travel parallel through it to be effective. I was actually wrong, placing it hard up against the LED it was actually very effective. Below are some examples of a polarizing film I have.

No PBS, both orientation. You can see the light is equal for both planes.





And when the PBS is used. You can see how the one plane is converted to other with the one polorizer being lighter than both before and one being darker showing that is does convert the polarization plane.



Now this is with my led on a low setting, you can imagine the difference it could make to the brightness of low transmittance LCD panels that have higher contrasts.

So without having the correct fly eye lens to match you can only get a 50% conversion out of this but seems worth it.

The downside is the color artifacts, you get a slight green and purple coming off. Im hoping this is due to the joints between the PBS and if I make a small grid structure to block the light hitting these points.

Also this will enter into my light tunnel so should get diffused with the other light to a point you wont see it after the LCD panel.



email rsschmit@gmail.com
Reply
Like

Schmit01
Advanced Member
Schmit01
Advanced Member
Joined: 22 Jan 2013, 00:38

15 May 2017, 20:39 #58

Received my 600mm fresnel lens from the Fresnel Factory today and after testing am very happy with the results.
Everything looked perfect, I projected the area 1 meter past the fresnel to be 100% sure there was no deflection or artifacts.

Will now proceed with my new build and will post shortly.

Cheers
email rsschmit@gmail.com
Reply
Like

jthedd
Advanced Member
jthedd
Advanced Member
Joined: 27 Jun 2012, 18:49

16 May 2017, 08:05 #59

good deal looking forward to following the build.

I started a new build last weekend,

was only able to get it rough cut out

I will also start a thread of the build.

See if we can get the forum rolling again with some new builds.


Jeff
jthedd@yahoo.com
Reply
Like