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iView Limited has developed a compact light engine for LightCrafter4500 0.45" DMD. To explain the light engine, I have disassembled one of our early units by removing the bottom thermal plate, heat sinks, and driver board. Note that any disassembly of the light engine voids the warranty on the LightCrafter4500 system. Note that opening the light engine allows dust and smudges to collect on the optics. Also, the opening of the light engine might move the optics out of alignment. Both conditions will distort the output image.
The following photo shows the top side of the light engine. The flex cable connects the 0.45" DLP4500 DMD to the driver board. The DLP4500 is on the top at the end of the flex cable and behind the heat sink. The DLP4500, DMD heat sink, and flex cable are glued to the light engine. The connectors on the bottom are for the Red, Green, and Blue LEDs.
Disassembling the light engine is fairly straightforward with the focus portion screwed on the light engine. The focus optics are held to the light engine with the four screws around it. The rest of the internals of the light engine can be seen by removing the top plate.
Each LED has an optical collimator to collect the wide beam of light from the LED and produce a narrower beam. This narrow beam of light passes through a set of dichroic mirrors that reflect a specific color of light while letting other colors of light pass through it. The dichroic mirrors recombine the different colors of light into one co-linear beam. The recombined light passes through a fly-eye and condenser lens that provides uniform light intensity. The light bounces of a mirror and passes through a total internal reflection (TIR) prism. The light is directed towards the DLP4500 DMD and goes through the focus optics.
The next image shows the paths of the red, green, and blue light. Note that the TIR prism has been removed.
The LED used in this engine are:
A few more pictures.
Removing the heat sink behind the LEDs:
Removing the LED boards:
Removing the DMD heat sink. You can now see the DMD placement on the light engine:
And finally, light engine without DMD, LEDs, and TIR prism:
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I have some questions,
1. What's the reflectivity of the dichroic mirror in front of the red LED?
2. The dominant wavelength of the red LED is 617nm, right? is there higher wavelength red LED?
In reply to George:
The transmission of the red dichroic mirror is roughly above 95% from 420nm to 550nm. It has close to 99% reflectance between 600 and 650nm. These values might change or shift due to variations in coating during production.
The transmission of the blue dichroic mirror is roughly above 95% from 510nm to 600nm. It has close to 99% reflectance between 400nm to 480nm. These values might change or shift due to variations in coating during production.
The light engine has as Red LED the OSTAR LE A A Q9WP from OSRAM with a dominant wavelength of 617nm. In why Q9WP package, i am only aware that OSRAM only produces amber light. You can find more information of these LEDs in this link.
In reply to PedroGelabert:
This is very interesting insight in the LC 4500 optics.
One important question for me is whether there is a way to lock the focus setting reliably once it is focussed to the correct distance.
In reply to Erik Klaas:
The focusing mechanism is a pin that rotates in helix fashion around the focus optics. As you can see in the attached image, the pin has a hole that could be used to hold/tie it in place. There is also another screw hole in the focus barrel that can be used to hold the focus mechanism in place.
I have a question concerning the light engine and the illuminance of the 3 LEDs. Could you specify how were the values provided on pages 23-24 of the User manual determined? I'm referring to the graphs of LED illuminance. Is this illuminance at the output of the light engine, or the illuminance of the LEDs without any optics? If the latter, is there any data available on the effective illuminance (or better yet, on the irradiance) at the output of the system for each color?
In reply to Zuzanna Piwkowska:
Yes, the illuminance is at the output of the Light Engine. For illuminance at the output of each LED, refer to OSRAM data sheets. The LEDs are at the end of this thread.
Thanks a lot Pedro for this info and also your reply concerning the noise. I think the link you posted refers to the LEDs in the first LigthCrafter though, right? There are other LED part numbers listed above in your original post concerning the light engine, are these the ones for the 4500 model?
Also, just to make sure I understand correctly: the irradiance values are in lux, ie in lumens/sq meter, so were they measured for an image at 1m, ie of 33.3'' diagonal size (I'm going by the iView specs here)? I'm trying to recover information about the total light flux in fact, is that the way to go? I get an image area of 0.324 sq meters at 1m, so that gives me for ex. 110*0.324=35 lumens max for the blue LED. Could you confirm or else specify for what total image size the values were taken?
Thanks a lot!
Sorry about that. You are correct that link was the 0.3" LightCrafter LEDs. The LightCrafter 4500 OSRAM LEDs are:
You can find the data sheets here.
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