# Creating a light with a straight (parallel) beam



## maxread (Jan 5, 2015)

I hope I've found the right place to ask this question.... I'm creating a stage prop. The idea is to create a "cage" that has vertical bars of light (20) radiating from a platform (that I've already made). 

My plan was to stick GU10 LEDs in a 55mm tube with the lens at its focal length away from the LED.

I bought some of these:

http://www.ebay.co.uk/itm/161251842...49&var=460299955897&ssPageName=STRK:MEBIDX:IT

and some planar convex lenses:

http://www.ebay.co.uk/itm/141510455935?_trksid=p2060778.m2749.l2649&ssPageName=STRK:MEBIDX:IT

and stuck it together. The results are OK, but the beam still diverges.

I improved matters by adding an occluding disk with a 10mm hole in the centre in front of the LED, but I'm still not happy with the results.

Any suggestions would be much appreciated.

Thanks, Max.


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## Ken_McE (Jan 20, 2015)

Lasers?


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## CoveAxe (Jan 20, 2015)

If it doesn't need to be too bright, the easiest way to do this would be to put an LED at the end of a long tube (a few feet long, at least). Then cover the other end and put a small hole in it. The light coming out of the small hole will be fairly close to being parallel. You will lose a lot of brightness though.

Your only other option is to use complex optics, and I would just say good luck with that.

Personally I think your best bet is to use lasers. You could also just use slightly opaque plexiglass rods and shine a light at one end. The whole rod will light up if done properly.


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## onetrickpony (Jan 20, 2015)

It will work somewhat better if you remove the reflectors, but you still have a rather large emitting surface with those leds, which will make a more dispersed beam. The smaller the light source, the tighter you can get the beam.

What's your budget?

If you can't remove the reflectors, would it be possible to put black tape over them? You can't mix optics like that without some serious optical engineering. Btw, you'd have to tape the reflector surface, not just the plastic or glass area above. That wouldn't work.


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## TEEJ (Jan 20, 2015)

Lasers do this w/o as much work. There are beam expanders for them that can make the dowel of light fatter if the "bars" are too thin. Some lasers, such as 445 nm (Blue) can have a rectangular beam, and, you can focus it to the width you want, etc.

ALL flashlight beams will be conical to a degree, a ~ 1.3º beam angle is about the best you can get with aspherical lenses, etc...and that would be VERY expensive to get that tight a beam that way.


What is the distance the "bars" cover in length, and, how are you terminating the end points so they don't reflect/glow/ruin the effect?

What is the "bar diameter" you prefer?


Do you have color preferences?


If you DO have to have a conical beam, can you offset the start/end points so that the fatter end of the beam is FARTHER from the viewer/the thinner end is NEARER to the viewer, so that from the viewer's perspective, the beam appears to be of uniform diameter? (Assuming the offset is not obvious to them)


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## onetrickpony (Jan 20, 2015)

I was just thinking if he already spent his budget...


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