Note: photos below.
I think I may have a uv lamp configuration that will be usable with almost any dlp projector, it also does not involve using optics. Let me bore you for a second, when I was 10 years old or so my parents bought me a microscope, included with this microscope was a lamp used for illuminating slides. The interesting thing about this lamp was that it consisted of a base with a bulb in it with a curved piece of acrylic coming out of it, the acrylic was in the shape of an elephants tusk. What I found interesting about that lamp at the time was that it delivered the light from the bulb in the base to the very tip of that acrylic “tusk” very efficiently. I’ve been trying to get uv from the 20w led to the projector light tunnel using optics in one configuration or another with decent success but I thought I could do better, one of the ideas I thought I would try out was using an acrylic light pipe.
The acrylic light pipe idea had been floating around in the back of my mind for a while so one day when I was near a plastics fabrication/supply business that I’ve been buying from for some time (they let me buy scraps and remains of various types of plastics) I stopped by and purchased some acrylic rods. I finally got some free time and decided to try the acrylic light pipe idea. I did a quick design for a mount for the uv led, heat sink and acrylic rod and cut it out on my cnc router using 3/4″ polypropylene. I cut off a short length of 1/2″ acrylic rod and sanded the ends with 220 sand paper then I “flame polished” the ends by lightly heating them with a propane torch. After assembling the parts I “fired up” the uv led (uv blocking glasses on – safety first) and what I saw was a very high percentage of the light from the uv led coming out of the end of the acrylic rod, there was a minimum of light loss at the led/rod interface or out of the sides of the rod.
Before fabricating the acrylic rod assembly I did a bit of research on acrylic light pipes and found that they used “total internal reflection” basically the acrylic rod acted like an optical fiber, if the ends and walls of the rod were polished there would be very little light loss, may attitude upon reading this was basically “yeah right”, my attitude changed completely the second I turned on the uv led and found that an extremely high percentage of the uv light from the led was coming out of the end of the acrylic rod. Potentially what this means is that an acrylic light pipe can be constructed that tapers down to the size of the dlp projectors light tunnel (around 1/4 inch) and the light from the uv led can be channeled directly into the light tunnel. Lets bottom line this, this is an efficiency game, if you are going to use a uv led for 3d printing it’s about getting as much uv to the dlp chip and out the projection lens as possible. Using an acrylic light pipe may be the trick that makes using a reasonably priced uv led feasible as a light source for a DLP projector used for 3d printing. When I get a chance I will fabricate a tapered light pipe to see if I can efficiently channel the light from the uv led directly into the dlp projectors light tunnel without any intervening optics.