Fluorescent light source brainstorming thread

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#3
But we don't need a point source

I am currently working on a projector using the Lights of america 65W flourescent bulbs. I will use either 2 or 3.

A point source is not necesary. But you will need enough flourescent light to fill the screen evenly.

I am using the sharp QA-1200 and even though the 65W flourescent bulbs are big there are still some dark area's (near the base of the bulbs.

I am thinking of getting rid of the fresnel (flourescent is not a point source so we don't really need one). I am thinking of using a plastic diffuser like those that are on overhead flourescent fixtures.

LCD panel monitors use something similar (the light pipe). And they don't have a point source light.


We don't need a point source, just even light over the entire screen area.
 
#4
Re: But we don't need a point source

dogon1013 said:
I am currently working on a projector using the Lights of america 65W flourescent bulbs. I will use either 2 or 3.

A point source is not necesary. But you will need enough flourescent light to fill the screen evenly.

I am using the sharp QA-1200 and even though the 65W flourescent bulbs are big there are still some dark area's (near the base of the bulbs.

I am thinking of getting rid of the fresnel (flourescent is not a point source so we don't really need one). I am thinking of using a plastic diffuser like those that are on overhead flourescent fixtures.

LCD panel monitors use something similar (the light pipe). And they don't have a point source light.


We don't need a point source, just even light over the entire screen area.
Click to expand...

This very interesting. I have a few questions though. First, what exactly is a plastic diffuser? Also does anyone know the physics behind fluorescent lights and why they don't have a point source.
 
#5
#Dogon

'A point lightsource is not neccesary'

Hehe, strictly speaking you are correct. But what ywh tries to say is that you need uni-directional light for projection. All light has to travel from a known point to another known point. If not you can never get a focused picture. A normal lcd monitor doesnt need uni-directional light because its NOT A PROJECTOR!
lol
 
#10
Rapsac, I think we are both right

rapsac said

All light has to travel from a known point to another known point
Click to expand...

and light does travel from a known point to another. From the lcd screen (after being color and brightness filtered), Through the lens, and onto the screen on the wall.

Now how the light gets through the LCD screen and into the lens is our dillema.

With a near single point light source (filament and arc type light bulbs) we can use reflectors and lenses to get nearly 100% of the light going through theLCD screen at the correct angle to allow it to be collimated by the lens and projected onto the screen.

A flourescent light is more like millions of small singlepoint light sources grouped together. Every little bit of phosphorous coating on the inside of the glass tubes acts like its own point source. Overall the brightness of the bulb may be comperable to a high powered single filament bulb but because there is no single point source to focus lenses and reflectors to it becomes impossible to use nearly 100% of the light. We may be able to use only 50% or less of the light to actually project our LCD image.

But since the lights themselves are MUCH cheaper and much more electrically efficient we can easilly use more of them to offset the optical inefficiency of the diffusive bulbs.

so how do we do that:

I am not exactly sure but I am going to use 2 or 3 of the LOA 65W flourescent bulbs to cover the whole area of the LCD screen with light.

I believe that a diffusive material (clear or white plastic) can be used in order to spread the light more evenly just like it is used in overhead flourescent fixtures.

Currently I have 1 65W bulb working and it does project enough light through the Sharp QA-1200 screen to be viewed well. The problem is that the bottom of the screen is darker than the top.
I am adding a second and maybe a third.

I will keep in touch about the results
 
#11
How efficient are those lights? I thought MH bulbs were pretty efficient at +- 80lumen/watt.
And with point lightsources you can get about 60% going towards the lcd at the correct angle. With a non-focusable light you wont get more than 1-10% efficiency, and the rest will just ***** up those few %
 
#12
efficiency

Well Lights of America "claims" their 65W flourescent puts out 8,255 Lumens so that would put it at:

127 Lumens per Watt.

The biggest benefit would be the reduction of heat. The lights come sealed in a plastic enclosure, But I think I am going to provide a fan for ventilation. The bulbs do get hot, you couldn't hold one after it has been on. But it does not get as hot as an incandescent bulb.

I also just noticed that some of the light bulbs have a yellowish light and others have a blueish light. Luckilly I got 2 with a blueish tint, I don't think I can use the third one, there is very little room to mount it.
 
#13
I've been very busy for the past few weeks but when I was still playing with my projector regularily I noticed that it is nearly impossible to focus.

It uses 2 of the 65W LOAs and a 10.4 Sharp screen. I'm pretty sure that it has to do with using a fresnel to throw the picture because I could get one portion of an image to focus but never the entire thing. Chalking it up to bad parallel alignment of the lenses. I think that if I had a real lens that was easier to move in and out I could get it to work.

Brightness is also questionable at best. It can easily be seen in a completely black room, but with a light on there is not a chance you are going to be able to watch anything. Next week I do not have any classes to go to so I will be able to work on it with any luck at all. I still think it is doable if I build an enclosure, paint it black inside and mount everything better.... If I can get rid of that annoying focus issues.
 
#14
LaserLine said:
Well Zark did it with a smaller LCD. Is there any way to copy that idea, but just custimize toward a 15" LCD?
Click to expand...

Yeah, the idea could be copied to use with large LCD panel. Only thing you need is a projection lens with 15" diameter:


An externally hosted image should be here but it was not working when we last tested it.


by the way, the image is copied from zark's website. you can see the LCD is close to the projection lens so most light come out of the panel could be collected by the lens.

:bulb: can someone calculate that if a large fresnel lens can be used to collect light from the panel before the projection lens?

lights===LCD===Fresnel>>>------------------------projection lens
 
#15
I was thinking of another flourescent idea. Gut an OHP (cut out the bottom) and put a 12"x12" bank of flourescent tubes in the bottom (tightly enough for the tubes to be touching each other. Put a fresnel or similar above this 12X12 square to more or less straighten the light, the let the OHP's fresnel do the rest.

Don't know if it would work- just bouncing around ideas. regular OHP bulbs die too soon, and the 575 MH bulbs used in some pj's are ridiculously overpriced. (about $400 for a 750-1000 hour bulb)
 
#16
Did you look at post six? YWH and his friends are old hands at DIY pj's. I'm willing to bet they were bright enough to put a fresnel lens over the lamps...and YWH's cryptic comment?

all fail!

I think a "cold" light source that lasts years would be awesome!
But we will need to get past the idea of using a "non conventional" light source in a conventional manner.

zardoz




JeffStickney said:
I was thinking of another flourescent idea. Gut an OHP (cut out the bottom) and put a 12"x12" bank of flourescent tubes in the bottom (tightly enough for the tubes to be touching each other. Put a fresnel or similar above this 12X12 square to more or less straighten the light, the let the OHP's fresnel do the rest.

Don't know if it would work- just bouncing around ideas. regular OHP bulbs die too soon, and the 575 MH bulbs used in some pj's are ridiculously overpriced. (about $400 for a 750-1000 hour bulb)
Click to expand...
 
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