Haven´t been online for several months, I just found back the forum and re-subscribed for telling you the rest of the story:
I recently GOT ONE! After a painstakingly difficult search I found out that they are resold by a company in Germany, but prices are above 350 Euro for a sheet of 12*9 inches. I managed to talk the dealer into selling me a VERY small sample piece, and I applied it to my 3? white LED tourchlight from german superstore ALDI for a first test.
-absolutely uniform colour distribution, no yellow rings and violet spots anymore
-semi-gaussian light intensity distribution with 30° FWHM
-unbeleivable 91% transmission (not veryfied by exact measurements, but obviously true).
Impression to the eye: The sensation is, that the light spot looks unsensational in every aspect: round and white. For me, it shifts the value of any LED lamp from "a nice toy, but unpleasant for the eye" to "a perfect light source".
To the optical background: A semi-random structure ("random" in macroscopic aspects, but "structure" in microscopic aspects). Its like a well-tuned combination of a projection optic and a ground glass in one single sheet of plastic. You can even get types which make a rectangular-shaped beam profile from a "round" collimated source.
In combination with a LED, the LED lens works as a condenser lens and collimates the light (more or less). The stray light from the unperfect LED lens and housing reduces the benefit to some extend, but as long as you don´t want to have it totally black besides the main light spot, that doesn´t matter.
For projection purposes, it can throw ALL the light from the rear projection screen to the viewer (or transfer camera in my case), no light will be wasted by illuminating the surrounding walls, ceiling and floor. But due to the small size of the sample, I couldn´t test that.
I am very interested in further discussion about how to make holographic diffusers by ourself - for example: One could use this program which is able to abuse a CD burner to create pictures on a CD or DVD surface. The algorithm for those structure patterns are publically available, so one could burn that picture on a DVD, remove the reflective coating - and, voila!.... etc.pp.
Fascinating and thanks for coming back to share your experience with it. I have always been a fan of the holo-diff films and they make a great beam even better. Well, except for throw.
From what I know about the hologram patterns, derived from my short experience working in the holo-diffraction film business (for decoration, not illumination management), you cannot get the same pattern from a burnt CD.
In any case, let's hear about more applications of this type of technology.
The "picture-burning abuse" is -or has been- a built-in feature of some burners, supported by the software in the box only. I have not yet seen an actual example, but in principle the dot-resolution of a CD should be just sufficient for holographic purposes. I guess one has to use a DVD though, because if you remove the aluminum coating of a CD, the pattern is gone. A DVD stores the dots in the plastic.
That was just a proposal for a further discussion how to cut costs for holo diffusers. They are so wonderful, the principle is so straight-forward and simple, but prices are rediculously high.
Nevertheless, I think if I make some extra hours at work to buy the original POC products is still cheaper than experimenting with self-made ones. Patent issues could not be a subject because the principle has been published in Physical Review / IEEE transactions (scientific papers).