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| uV LED lightbox |
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| Davy:
I have loads of 5mm ultra bright uV leds, the viewing angle is 20deg. wondering if 15mm led-to-led spacing would be OK to avoid dead spots or shadowing in a uV exposure box? Dave |
| OM222O:
you didn't mention anything regarding the power dissipation. that's the most important thing, so if you have enough heat sinking or active cooling, it should be fine. |
| ajb:
Depends on distance and the array shape. It also depends on the field distribution of the LEDs, depending on how even of a distribution you need for your application. For a rectangular array at 15mm center-to-center spacing you need the projected spot size to be at least 22mm in diameter to avoid a dead spot in the middle. For a hexagonal array you need a 15mm spot. Some trigonometry based on the 20mm viewing angle will give you the distance you need between the LEDs and the projection surface. Realistically, the output of the LED doesn't drop to zero immediately past that 20 degree angle, but the exact shape of the dropoff depends on the LED. The datasheet hopefully has a polar graph that shows the approximate field shape. |
| sleemanj:
The wider you space the leds, the taller you need the box to be. With a 15mm spacing your box should be around 45-50mm from the emitter to the artwork. However, don't be afraid to use a diffuser. I've made a number of UV boxes and used diffusers in most of them, usually with one diffuser layer halfway between LEDS and glass, and sometimes another diffuser directly on the bottom of the glass. You can still do plenty fine enough traces no trouble with diffuse light, I rather have an even but diffuse lighting than have hot-spots where every led is. |
| Davy:
Thank you to you all for the response. These are through hole domed types, too close and I get good spotlights, the distance from the LED's to the 'target' seems to be around 40mm when trying three LED's lashed up, think I'll lash a couple of banks up on veroboard (I hate that stuff) and have a play, I've a feeling 10mm spacing might be an overkill and need have a play here. The LED spec-: 3000mcd. 3.2 -3.8V @ 20-30mA Viewing angle is 25 deg, not 20 deg. as I said before. I read somewhere about glass being opaque to uV, I'll have a dig round later. I replaced bulbs in a 'S' meter once using two white SMD LEDs and used a diffuser from a flat panel screen to stop the glare, it worked a treat, the stuff looked like frosted Mylar.... I need do some playing here. Dave |
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