The goal of the light engine in the LL design is to collimated as much of the lamps light as possible to normal incidence with the panel. It is a brilliant system. But unfortunately, this imposes a few inherent limitations:

1. Large arc tube's throw light too far off normal incidence to be collected by the projection lens.

2. The unaltered design insists on a single point light source.

3. The collimating fresnel is lossy. It introduces reflections, material transmittance issues and total internal reflection.

4. Only the light that makes initial incidence with the collimator is useful. A great deal of the light does not impact the fresnel. Other light cannot be recycled.

5. Without a fairly complicated light recycler, 50% of the light that makes incidence with panel is absorbed.

6. Designing a light recycler for a point source is inherently limited.

I have a theory about a diffused light source that may largely eliminate these limitations. The problem being it has not been done, and has at least a couple theoretical limitations of its own.

I'll start with a basic design: Imagine a light engine who's containing box has a white diffusive reflective inner surface. Flat white paint for example. The bulb would sit in the center of this box without a reflector. Basically, it does not matter where in the box the bulb is located.

The 6th side of the box is the Lexan heat shield, followed immediately by the panel.

The light that exits the Arc Tube and heads straight at the panel would be projected. The light that is off normal that impacts the panel may or may not be projected based on what area of the Collector Fresnel it impacts. The light that bounces off of any area of the white diffusive lining will have at least a chance at making impact with the Panel, but will it too will likely impact the Collector in such a way as to miss the Projection Lens. All the while, as with the Collimating Fresnel design, 50% of the light will be absorbed by the Panel's Polarizer.

This is probably not a design worth pursuing at all, but it set's the stage for something much more advanced.

First: what if we could somehow reflect back the 50% worth of light that is not useable by the panel, have it bounce around the engine a while, until it is of the proper polarization axis to not be absorbed?

Second: what if we could somehow reflect back the enormous amount of light that is on the wrong trajectory to make proper incidence with the Collector, and the Projection Lens?

Then we would have a diffused light engine capable of taking any sized bulb, any type bulb, and theoretically make much more efficient use of the light.

3M provides optical films in their Vikuiti line that do exactly this. That element that would satisfy the first parameter above is their Reflective Polarizer (DRPF), and the second is their Prismatic filter (BEF).

The BEF works to allow only light that is up to 35 degrees of normal incidence through, and reflect the rest. 35 degrees seems to be too much, but there is a gradual taper from 100% transmittance at normal to 0% transmittance at 35 degrees. So it's not so bad.

The design I propose is ordered as follows:

1. Arc Tube.

2. Lexan.

3. 3M Diffuse Reflective Polarizer Film.

4. 3M Prismatic Filter.

5. 3M Prismatic Filter at 90 degree orientation to the first.

6. Panel and everything else as usual.

With a light engine having a diffusive, highly reflective inner lining.

The reflective polarizer needed must be of the same polarization axis as the stock polarizer of the projectors panel. The polarizer chosen must also not be of a diffusive variety. I don't think this exists, and that is why I have placed the BEF after the DRPF. That will aid in correcting for the polarizer's diffusion. There are 2 sheets of BEF mentioned because each sheet only rejects light on one perpendicular plane.

Problems:

Having the light bounce around the in the engine will knock out brightness for each bounce. Further, light reflecting off the Prismatic Filter will need to pass through the Reflective Polarizer a minimum of 3 times before it is useful.

Still, something worth looking into if you ask me .

Mark.

ok, ya lost me ;-) why a diffusive inner lining, why not FS mirrors?

Because a mirror will not depolarize the light, and it will therefore not be given a second chance at passing the reflective polarizer.

Also, a diffusive lining will always redirect at least some light back in the correct direction. With a mirror, things would have to bounce around for quite a while before any of the off normal light could be used.

Mark.

knew I was missing something simple.... what about having diffusive 1/4 wave plates in there? away from the mirrors? no I don't know why. just popped into my head....

Because, unfortunately, that is a complicated thing. There aren't any diffusers that I am aware of that do not depolarize light, and light needs to be polarized to circularly polarize, and we need to diffuse in order to get the angle of incidence correct. Hope that makes sense.

Mark.

I've considered something like this myself. One issue:
Polarized light hitting the BEF will have its polarization modified in a semi-random fashion as it passes through, making the reflective polarizer less (or not at all) effective at supplying properly polarized light to the LCD. I think that's why they always have it right next to the LCD on their web demos:
http://cms.3m.com/cms/US/en/2-136/ikrzrFX/view.jhtml

I've been doing some ray-tracing to see exactly how the prisms help to collimate light, and they seem to be more efficient if the light enters at an angle other than 90°. This may actually be beneficial for eliminating a central hotspot, but my (virtual) testing also shows that a large portion of the light will still miss the triplet. (Light exiting the LCD must be within ~+/-5° to hit.) On the (pardon the pun) bright side, using 3M's claimed 60% improvement, you're doing as well as you would to add a reflector and fresnel. There may be ways to enhance it further though.
http://multimedia.mmm.com/mws/mediawebserv...tsssH&B1nytAvR-

They have the Reflective Polarizer next to the panels because otherwise light that is off axis needs to pass through the polarizer at least 3 times. This is a modification that I made, as it could help correct for the worry that it seems DRPF is slightly diffusing. Wether that position is chosen is just a starting point.Cool . But raytracing this cannot be easy. Are you taking into account the critical angle of 35 degrees? I would really like to see these raytraces. It would certainly be a balancing act. Can there be enough benefit to outweigh the limitations is the question.

In our case, there is actually more than a 60% benefit (unknown losses). One of the critical aspects is that it gives us the opportunity to at least utilize to some degree the light that was not impacting the fresnel, and multiple light sources or irregular shaped light sources can be employed.I'm not sure what you mean?

Mark.

Here's what I'm using to ray-trace. IMO it's not high enough quality software to cough up the registration fee, but for a little testing it's not bad.
http://hometown.aol.com/jslsoft/optlab.zip

Any screen shots of the raytrace?

Mark.

What the he11? Why did that post 4 times?
:angry:

Anyhoo...My calcs... http://www.lumenlab.com/forums/index.php?showtopic=8594 ...show a ~60% increase in lumens when you use a reflector in your projector. This recycling light engine would seem to provide a similar gain, assuming that the graphs on the second link are at least semi-accurate for our purposes.

Here's a quick and dirty screenshot. It's much more effective to use a single ray and manipulate it in real time. There's too much information to put into one picture.

Perfect. That pretty much confirms the way I have ray-traced it by hand in the past. It seems that it is best to say that it is not a film that allows only head on light through, but rather a film that only allows light through that will end up mostly at normal incidence. The light can come from the edges and get refracted. So I agree, this could help even out the image lighting evenness, as the head on light is actually rejected. That means that a great portion of the projected light will be sourced from a diffused reflection. A lossy thing.SwordMaker estimated that 19.5%+- makes incidence with the fresnel in a 15". Yours says 9% or so? I think the 60% increase with a reflector is a good guess. Maybe a bit more in my opinion, though. Of course light does need to pass through the arc tube (another thing that diffused would fix).

Yep, it is these kinds of numbers that has me confident that this could do the trick. As a very rough figure, it looks like 19/20ths of the light is ignored by the collimator style setup without a reflector. A lot of that light would at least be seen with the diffused design. It seems this system would have to be remarkably inefficient with that recycled light to turn out worse.

2000% improvement anyone? .

Of course, don't read into that too much (it is very rough and doesn't take much into account at all ). But it is that reasoning that has me a bit confused about you bringing up only the 60% polarization recycling?

I guess I should clarify. You can gain a rough estimate of 60% with polarization recycling. That is a major improvement, and obviously a major component of this design. However, even more major is the 1000% (3 zeros) that can be recovered by utilizing light that is missing the fresnel altogether. That estimate is likely too good to be true, given the spillage and absorption but it certainly gives us a lot to work with .

Mark.

Ok how much would all this cost?

What kind of reflector are you talking about for a 60% increase?

The only numbers I know of for a typical spherical reflector placed behind a MH lamp show a measured increase of
about 15-20% (from memory). Not exactly anything to write home about but worthwhile when we're searching
for any detectable increase.

Mark, this is a very intriguing idea. What is more intriguing is the simplicity of the construction. As I see it, the only unknown cost is the 3M Diffuse Reflective Polarizer Film and the 2 3M Prismatic Filters. I think that the theories behind it should be discussed a little more (by people who understand optics alot more that I), but I think a quick test construction would conclude whether this is viable or not. Even if your initial assumptions are off by a lot, 2000% provides a large margin of error. That means if the theory works at all, it would be very visually apparent with the test box. So...

If we can establish the cost of these 3M products, we could have a test up and running relatively soon. I for one would be willing to contribute to the cost of the 3M products, and I'm sure there would be a few others around that would be willing to invest a few bucks into this endeavour. After all of your efforts spearheading the antiglare removal campaign, I am very excited what your contributions to the light engine will produce.

Cheers,

Rhino

well, the DRPF runs 55$ a sheet when you buy 10 sheets(I have 2 right now, but they're only 11" square, and not the most transmissive variety, but more than enough to test the concept) I can't imagine the BEF is more expensive...

mark: will BEF II 90/50 work?

edit: oh, 3m says "I checked with our tech service engineer. DBEFE has no diffusion." that would be the embossed reflective polarizer

so let me get this straight, the lining of the engine needs to be diffusive so it depolarizes the light, true? the best option would be something that is diffusive and highly reflective true? how about something diffusive placed(or painted ) over a mirror? I know tha LFusion mix does not depolarize(I think it was elken over in the other thread right?) any ideas? or am I off the track again? ;-)

edit: hey...maybe a use for all the anti-glare thats been removed?!!!

this is actually really close to how a laser works.

Please respect that I don't want anyone contacting 3M sales until has been perfectly established, and we can say definitively what we want. These films are meant to come in expensive boxes of 10. Technical questions are fine, but ask them here first. I have only posted the basics of the physics involved, so I may be able to help.

We want a bit of time to run over exactly what to expect and what is needed. Even looking at the ray-trace above, I can see there are some discrepancies with the behavior of this film in writing. It was said to have a critical angle of 35 degrees. At that point zero light is meant to pass. So far, I have only seen BEF with 90 degree bevels. Different angles will result in different tolerances.

Mucho ray tracing should be done. If anyone wants to do some more ray-traces, then make sure you get the material density of the BEF pretty close. Also, make sure your ray-tracer is definitely taking into account refraction and total internal reflection. That is the primary principal that this is based on.True .Cost of diffusive light engine = The cost of Brightness Enhancement films = $176 US

But bear in mind:

Cost of Fresnel light engine = The cost of a condenser fresnel + The cost of a reflector = $24.99 + $15? = $39.99Yes. Both direction, and polarization axis should be diffused. If it does just one, then you are only going to gain that component of the design.

Just to be clear: when I say 1,500% (a bit more on the money) I am referring to how much light this system works with. A lot of that light will spill around the lens. A lot a lot. The question is, exactly how much? And what if I have the huge new pro lens? 1,500% is a fun amount of light to play with .Exactly . It would be a balance act again there to get good enough diffusion, though. The truth is, there are some materials that are flat diffusive, with full 180 degree direction diffusion, that are nearly 98% reflective. However, I think for initial testing, a good quality titanium white paint would establish the feasibility. But that kind of thinking is right on.I was guessing what the new Pro one could do. I just took into account the idea that it is thought to be around 50% more efficient and guessed what the current reflector is. Sorry for the half hearted dodgy guesswork there. It's not like me to do that. The basic diffusive design doesn't even have a reflector, so I got lazy . You are right, even the newest most optimistic estimates seem to be placing the new reflector at around 42% effective.

edit: messed up the pricing guideline. More expensive now.

Mark.

Backlight Design

... and some more

work to do now... more input later..

Mark, The design you've described is very similar to some existing backlight designs. Why don't we just try to figure out how to push a LOT more light into an existing backlighting system?

Oops....I meant Mark, really I did! Shouldn't post so close to bedtime.

While we will be using some of the same components, there are a few degrees of separation between thin CCFL backlight designs, and what I have proposed here. Not all the limitations of a monitor backlight system need apply, and there are some parameters that work great for monitor backlights that need not find their way into this design.

For example: Non of the components downstream of the prismatic filters can be diffusive. And the use of a rear mounted wedge or diffusive light guide, or spotted glass is meant to spread out in edge mounted light. They edge mount because it is the thinnest design that supports long thin bulbs and can at least be spread out by some means. Thinnest need not apply here. In fact, my design suggests a large gap surrounding the lamp due to heat, and the centered position I think is optimal based on the small arc tube.

Wether a diffusive sheet will be needed or even tolerable before the prismatic filters will be up for experimentation.

edit: I forgot one of the most important parts: I don't need to diffuse my trickery, as monitors must, because the Condenser Fresnel has a short depth of field.

Mark.

If I could get my hands on the components, this is what I would try first. (From the above post it seems that we might be able to drop the diffuser sheet. In any case, one of the sheets left over from stripping the backlight might serve this purpose). I'd also be content to test without the DBEF film firstly also.


7a Diffuser (Made from ??)

7b Vikuiti™ BEF II Film This is the current version of the original Vikuiti BEF I film, which has been out of production for some time. It features an acrylic resin prismatic structure coated on a polyester substrate. This is the highest performance member of the family, and incorporates structural features which helps avoid wet-out, which is an optical coupling that can mar the appearance of an LCD display. It is available in the standard 90/50 version, and a 90/24 version for additional moire avoidance. (I'd be suggesting the 90/24)

7c Vikuiti™ BEF Film – Same as above, oriented at 90° to the above layer.

7d Vikuiti™ Vikuiti™ DBEF-E Film This is the current version of standard Vikuiti DBEF film, which has been sold for years. The “E” stands for embossed. One side has a slightly raised embossed structure which acts as spacers to prevent the film from laying totally flat against other surfaces. This helps avoid “wet-out,” which is an optical coupling that can mar the appearance of an LCD display.

Here is more specific post of what is needed:

2 Sheets of Vikuiti Brightness Enhancement Film (BEF) II 90/24. 17" x 17" for larger monitors. $55 a sheet.

This film has a 90 degree prism angle, but has a 24 micron prism pitch. Down from the standard of 50 microns. This apparently improves the clarity by reducing optical coupling with other surfaces.

1 Sheet of Vikuiti Dual Brightness Enhancement Film-Embossed (DBEF-E). 17" x 17" for larger monitors. The installer must choose either 0 degree or 45 degree based on the polarization axis of the panel, or cut a large sheet to the correct axis (not easy). $66 a sheet.

Turns out DRPF is always cloudy. So it should be avoided. DRPF is a lower quality version of the DBEF-E, which is spec'd as transparent. Thanks for confirming that with 3M mikyd1954 .

We need to bear in mind that while incorporating this into the current Fresnel design does introduce reflection, it unfortunately would not satisfy the diffusion and redirection needed. A Fresnel design also unfortunately misses out on some of the key benefits of a diffused light engine. The most prominent being the 86 - 92% of light that misses the Collimating Fresnel altogether. There are a number of other implementation limitations. For a polarization recycler that is optimized for the Fresnel setup, refer to this thread:

http://www.lumenlab.com/forums/index.php?showtopic=8765

I maintain that the design I have shared (though it may seem simple) satisfies all the necessary parameters.

Mark.

can you explain a little more why and exatly what you think this will do?

The polarization recycling element:

A perfect polarizer is only able to extract half of the light energy from depolarized light. The other half literally gets absorbed by the dichroic element of the polarizer (usually iodine). The very first element of an LCD laminate is a polarizer. Therefore, around half of the light is not in use. An imperfect film polarizer (every one in existence) absorbs a further amount due to it's built in inneficiencies. 10% absorbed would be around the least that you would find. Therefore at best, a polarizer will be allowing only 45% of the depolarized light from the light engine through. The other 55% is converted to heat.

The use of a sheet of DBEF allows us to reflect back the 50% worth of light energy that was not polarizable. Specifically, it is the vibrational energy that represents the opposite vector that the polarizer passes.

It is important that the DBEF be of the same orientation as the LCD polarization axis. Otherwise, it reflects the light energy that would pass the polarizer, and transmits the energy that would not. Blackness .

It is also important that the DBEF not be diffusive. Otherwise it will throw all light that the second part of the system has worked hard to get in the right direction into a number of random mostly unusable directions to begin the tiresome process again.

The reflective polarizer is only half of this element. The other half is a diffusive surface that will scramble the unusable polarized reflection back into depolarized light. This is one of the purposes of the white lining of the light engine. The depolarized light then returns to the polarizer and begins the cycle again, until more light can pass. It will have to bounce back and forth like this many times before all of the light would be recovered in a perfect system.

The collimating element:

Only light that enters the Condenser Fresnel at roughly normal (0 degree) incidence is useful. Otherwise it will miss the projection lens. This is where the BEF comes into play. These films only allow light that would exit within 35 degree incidence through, and reflect back the rest. 35 degrees is likely too much, but the intensity of light that gets through to light that is reflected is thought to be a gradual decrease. A second sheet is needed at 90 degrees because each sheet can only reject light on one axis.

The light that is reflected back gets redirected by the diffusive lining into any number of different directions. Certainly the light is most likely to redirect mostly on the trajectory that it entered (and still not be useful) but not all.

The stray light gathering element:

This could be the most important aspect of this design. It is inherent to the design but can be mostly credited to the diffusive lining. Anywhere from roughly 86 - 92% of the light that the bulb produces is simply unusable because it does not impact the Collimating Fresnel.

By using a free-for-all diffused design, and collecting the preciously unusable light energy, I am hoping to capture enough of this light to make up for the inherent limitations of the diffused design.

Here is a quick drawing:

Click to view attachment

The gray box is the 5 sided light box, lined with highly reflective diffusive material or white paint.

The bulb is at the center.

The first sheet you see is the heat and UV shield.

The next sheet is the first BEF film.

The next is BEF film oriented at 90 degrees to the first.

The next is the DBEF reflective polarizer.

And then the LCD.

Mark.

Hmmmm.

What if the BEF film is not oriented parallel to the LCD, but at, say, a 30 degree angle?
Most of the light would be reflected back because it would not enter it at the correct angle.

Just a wild thought.

OK, I only suggest this as an initial test as it is relatively easy to accomplish with our current setups. The idea is to collect any stray light that has hit the collimating fresnel at an unusable angle, as well as trying to utilise the incorrectly polarised light that would otherwise be wasted. If you can, just look at the collimating fresnel during operation, I'm sure you'll be able to see light coming through it and spilling out to the sides of the LCD.

The ultimate setup is what mark has shown in the above thread, removal of the coll fres altogether. My suggestion is more of a 'proof of concept' idea.

I've done some rough guestimates on just how much light will find its way out the Condenser Fresnel. My calculations put it at about 1535 Lumens. But maybe it could be anywhere from 1000 - 3000 Lumens. I made a lot of assumptions. The current best number here from any system is though to be around 223 Lumens with a pre-condenser and reflector. 168 Lumens with the standard design. It all kind of hinges on wether a full 10% of the light be useable could hit the triplet (10 cm wide)? Hard to say.

Here is my deduction (very, very rough):

5280 Lumens would exit the Condenser Fresnel in a perfect world, with an assumption of a standard 16% transmissive panel (10% standard panel up 60% with polarization recycling). Taking IronGecko's figures for the Lexan, and Fresnel, 4178 would make it out. Taking into account worst case reflection off the new films (5% per sheet) brings it to 3071 Lumens. Bear in mind these sheets probably actually have an anti-reflective coating, but I'm trying to put together a worst case scenario. Lets say 50% (holy approximation ) of that is lost to the diffusive lining = 1535 Lumens. Would be interesting to build one of those cheap Big Screen Fresnel projectors on the end of this monitor (no good, but really bright).

I got most of my numbers from IronGecko's Lumen Calculator http://www.lumenlab.com/forums/index.php?showtopic=8594Yes, the DBEF needs to be oriented the same as the panel.

Mark.

Could we not be using some of the films from the LCD panels that we have disassembled in order to create our PJ's? The BEF could surely be approximated by some of those standard LCD display films?

Lurch.

Thanks . But this design really is a balancing act. I am going to see about designing some basic tests to get a rough idea of wether I am in the ballpark. With anti-glare, things were a bit more predictable.They need to have the same properties as the films described. A standard set of films used in most displays are only meant to diffuse. There is no light recycling component. My display had some DRPF, though. I wouldn't worry about actually getting the films. There are some tricks there. As mentioned earlier, I just don't want anyone to bog down 3M's channels until I know for sure what we want/need and if it is worth trying for sure.

Mark.

Sweet. I take that back. It looks like even inexpensive displays have some form of a prismatic filter. It is that sheet that seems like a linear fresnel. I just played around with a flashlight, and it seems to behave exactly as BEF would be expected.

This means that I have 2 sheets of BEF and a sheet of DRPF . This could get interesting.

It's pretty neat stuff. Works exactly as it should. At 0 degree incidence, there really is Total Internal Reflection. The light just bounces straight back like a mirror. At 40 degree incidence or so the light is collimated, and most gets through. It really does as advertised because it is impossible to get light anywhere outside of 35 degrees to the edge of the sheet. Hope that makes sense.

So someone could whip up a simple prototype quite easily . Unfortunately I don't have a projector right now, but anyone ambitious who kept their prismatic filter can roughly proof this without polarization recycling. It really is a Pro Lens mod I think, but who knows, it may work with a smaller lens. You don't need a Pro lens to see the difference, though. You could just multiply your brightness by the difference in area between your lens and the Pro. Then multiply that by 1.6 to account for the missing DBEF reflective polarizer.

The tricky part would be lining the light box white. The reflector would have to go, along with the collimator. Further, you would need 2 prismatic (BEF) filters to really give this a good go. Anyone game for a possibly pointless overhaul? Or prototyping? (Crickets? ).

You know, being that I base all of this on physics, VS having actually built a projector () I would appreciate absolutely anything that even approaches this design. Like:

Step 1: What does the image look like in your current setup without the collimator in place? My theory says that you will see a surprisingly bright center to the image, but the brightness will drop off ridiculously from there.

Step 2: Then what happens if you drop the reflector and have a white lining on all 5 sides? Should get a bit brighter all around.

Step 3: Then what about adding one BEF?

Step 4: The second BEF?

Step 5: The DBEF?

Choosing to do any number of steps along the way would be greatly appreciated, as it is a component, not a composite system. But step 2 is needed for all following steps.

Mark.

I'm getting really jazzed about this idea. I'm going on a hunt for the perfect panel: (Best Elmer Fudd imitation) Huh huh huh huh huh....Anti-wefwection in fwont, BEF and DBEF behind. I'ww get you if it's the wast thing I evew do...

Damn the torpedos, max the credit cards, let's go shopping! (You'll see that patience is not one of my strong points.)

How about a diffusive parabolic reflector??

But seriously, a highly polished reflector might bounce 95%+, how much are you going to lose on a white surface?

I've got some LCD backlight sheets here from my 17". I'll try some of them in the lightpath tonight.

Whatever interior shape is used, it needs to bounce the light to the walls. I think that any diffused shape would accomplish this just as well as any other, given that the source is coming form unpredictable random directions. I chose the box shape because it is simple to build. It really would be mayhem in there. There is going to be light flying all over the place .

There are white materials that are over 98% reflective. It's hard to say how inefficient this will be. I am skeptical, and optimistic all at the same time about this. It's a funny feeling .

Can you identify what variety of sheets you have? A reflective polarizer will block the image of your LCD monitor as you rotate it. The sheets of BEF don't look jagged. One surface is shiny, while the other has a linear micro etched look. A diffuser will look diffused, and have no effect on an LCD image when rotated. There are quite often two types of diffusers in the same display. One will have a chemically etched surface, and the other has a coating.

A sheet of BEF reflects head-on light so will block the light if placed between the Fresnels. And of course, they are directional. The etching needs to face away from the lamp. Removing the Collimator corrects for this. I am very curious as to what a diffuser will do, given the anti-glare science. BEF will eliminate the central brightness if placed behind the collimator. That would be weird to see.

I'm thinking if I had the components I would build a white box representing the light engine and build upward just stacking the components. You could easily stack up the components from either design in a few minutes. Fresnel Rings and focus are not important.

Mark.

I just checked the diffuser sheets off my 17" and 15" lcd's. They both have 2 diffuser sheets and a prismatic filter. They are arranged: Lightsource|diffuser|prisms|diffuser. Each of the sheets has a smooth and a 'rough' side, easily determinable with a fingernail.The most diffusive sheet is the closest to the lightsource. The orientations of the sheets are lightsource|smooth-diffusive|smooth-prisms|smooth-diffusive.


Just some quick preliminary figures and pics using a Maglight: (Lightmeter placed right on lens/filter)
No Filter: 18800 Lux


Lamp|Diffuser: 14100 Lux
(No Pic)

Lamp|Prismatic Filter: 9000 Lux


Lamp|Prismatic Filter|Prismatic Filter (90°): 4300 Lux


Lamp|Diffuser|Prismatic Filter|Prismatic Filter (90°): 5500 Lux


This last one is the 2 prism filters, no diffuser, lifted away from the light source a bit.


Edit: Just as antiglare is the enemy of the LCD, collimated light is the enemy in this design, in fact it seems that collimated light cannot be used

OK, scrap my original idea. I just fired up the PJ and tried placing the films inbetween the collimating fres and the LCD (even with the diffuser sheet). Nothing but black

Someone's going to have to build a diffuse lightbox....

Edit: Just for laughs I placed the 3 films on the projection screen: PJ|diffuser|prism|prism 90°|Wall. Hmm, I'm now wondering where I can get some of this stuff the size of the projection screen as it looks quite good.....

Yep:I think we're falling on the same page now .

Those sheets are designed to produce collimated light. The catch is that they reflect light that is not at the Normal (0 degree incidence). So to get collimated light out of them you need to supply off axis light. The optimal angle is somewhere around 45 degrees, with the other axis perpendicular to the etching.

If you had 2 prismatic filters, I think it is very likely that you also have a reflective polarizer. It may look like a diffuser (if it DRPF). Please follow my instructions above to establish what it is for sure.

These films are directional.

I like the idea of using the prismatic films overtop the screen. A great way to increase head on brightness (limit the viewing angle to 70 degrees). Nice. Unfortunately I don't think anyone produces these films as large as necessary. The only element that you need there is the prismatic filter. The screen should provide plenty of diffusion. In fact, you should be loosing brightness by incorporating the diffusers. Evidently, this is also how 3M's rear projection material works, but it uses spheres for the internal reflection.

Mark.

Oztang65: Could you be convinced to place a diffuser behind and in front of your panel (making sure it is not DRPF). As a side, I am very curious as to the result. Extreme anti-glare?

edit and looking at those photos it looks as though there is an embossing on those sheets? Are they not smooth and shiny on one side?

Mark.

Collimated light is fine. It just gets reflected back and diffused into another useable direction. The key is that it needs to meet a diffusive surface for that to happen. Hence the white walled box.

Mark.

Yes, I agree with the 45 degree angle, I held the torch under the single prismatic filter, tilted it to 45 degrees and nearly blinded myself. In fact, you can see from the photo of the single prism filter, it looks as though there are 2 lamps underneath at 45 degrees, likewise for the 2 prism filters at 90 degrees it seems as though there are 4.



No, i checked this out first, they are not polarised. One is off my BenQ 15", the other off the Magview 17" which is my current projection LCD



It just dims the picture.



All the sheets are smooth on one side, can't see any embossing.

OK, I just had another thought that might be effecting my PJ test. I have my replacement polar taped to the collimating fresnel. I might relocate the polar to the LCD and check it again (but not now, watching PJTV )

I've been fiddling with this a bit too. Cut my BenQ prismatic filter in half and rotated the halves relative to each other then placed them at various positions in the projector.

Found that the two pieces of filter would allow light to pass only if the smooth sides were placed back to back and rotated 90deg to each other. With this now passing light, the side presented to the light engine appears to the light engine as a bright diffuse screen.

The picture shows the filter halves on the bottom part of the screen and the two filter halves off-set from each other slightly which gives that black edge. The viewable part through the filters is slightly dimmer. The filters are placed between the collimater and LCD.

To be clear, the possible DRPF is not a result of two prismatic filters integrated together, it is a separate sheet that looks like a diffuser.

In that setup, the first filter will be refracting the light to the edges, and the second will be rejecting half of the light. I'll bet that as you rotate the one filter relative to the other, things go black on screen. This would occur because the light on one plane would miss the projection lens, and the other plane would be reflected by the second filter. This brings up an interesting point. The use of 4 filters: two facing the lamp, and two facing away would allow light at the normal to pass, and then re-collimate it with the last two filters. A cool exercise in the concepts. But I don't think that behavior will be useful as a recycler, though.

I have an even simpler proof of concept. Cardboard box lined in white . Ordinary light bulb in the center (white mount, non-directional bulb). Clear plastic on top. BEF, then the other BEF both with grooves pointing away from the bulb of course, and set at 90 degrees to each other. Then a condensing fresnel on top of that.

Now hold a piece of white card above that at the focal point of the fresnel with a 10cm diameter circle drawn onto it (This it the critical part I cannot do, because I do not have my Fresnel ). How big is the area? Where is the light most concentrated. This is what we need to know. If I know the area, I should be able to plug it in to my earlier guestimation to get at least an extremely rough idea of what to expect.

For fun you can multiply its brightness by 1.6 and that is the equivalent brightness that we have extracted from the ordinary bulb. Does the brightness seem impressive at all? The panel would eat up 90% of that light as well, but of course we are not using any ordinary light bulb. I just want some idea of how effective the Condenser will be with our 35 degree accurate collimation.

I think I will build a little version of this minus the Fresnel anyway. Might find a curve-ball.

Mark.

I'm glad to see that there's some progress here, I'd test my PJ and films out myself but I happen to be 600 Kilometers and a stretch of ocean away from it at the moment..

I'll keep an eye on the progress here though. VERY closely.

Lurch.

Ok, now I'm stepping out of my hole here. Been following you guys on this. Even tried the diffused white box. But before I provide my findings I want to be certain about some things that have been mentioned.

This prismatic filter that your all refering to...came from stripping one of you monitors, correct? Looks like this?:

The above was stripped from my Cornea I beleive. It is kinda diffused on one side and reflective on the other, however, the diffused side has a grid of diffused dots that form into diffused squares towards the middle of the surface. Heres a clossup of the dots.

That is the glass sheet with painted dots to help bounce the light around a bit. It is only meant to help spread the light out as a component of the light guide. Basically all that will do is cut down on output in a projector.

A prismatic filter is a film. One side is shiny, and the other has a very fine linear pattern.

A reflective polarizer looks like a diffuser or a clear sheet, but has polarization properties. It will black out an LCD monitor if you rotate it in front of the screen.

Then there are a couple diffuser sheets in there as well. They are not incorporated into the basic design.

I knew you would be on top of trying some of this . Thanks SIM.

Mark.

I have built a small prototype of the collimating aspect of this. Everything but the lenses.

It is a 3.5" tall box with a 5" x 5" opening. I lined the inside 5 walls with cutouts of Avery full sheet printing labels. I then punched a hole in the bottom, wrapped some iron wire around a flashlight bulb, and pressed it into the hole until it is flush to the bottom. So the filament is about a cm from the bottom. Then I wrapped electrical tape around the exposed sides of the bulb that the iron wire has taken care of. I then stretched a strip of aluminum foil over the bottom of the bulb to complete the circuit. A couple alligator clips later it lights up.

Without BEF on the opening, the output is quite bright, and it covers most of my roof. With 2 sheets of BEF it lights up about half my roof and is what looks to be about half as bright even within a fixed area. Neither of those behaviors were a surprise. The first is what BEF is meant to do, and the second I attribute to the fact that only the fairly Normal collimated light can illuminate any given spot on the roof. With an open top, there was diffused light from all directions illuminating the roof at any given point. Remember that Normal collimated light is all that is useful, so taking a 50% loss for what could be more overall collimation is expected. Problem is, I have no way of figuring how much of the light is collimated in either setup. So i remain skeptical.

Mark.