optics question - changing torch lens - advice needed

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 The Potato 24 Sep 2022

Ive got a fairly basic LED torch which provides good output, but the beam is quite wide, how do I make it narrower so it projects the light further. Would using a plano convex lens work? im fairly clueless when it comes to optics

Post edited at 16:36
 Billhook 24 Sep 2022
In reply to The Potato:

If you are "fairly clueless" as far as optics are concerned, how would you fit the new lens in?

I appreciate this is subjective but I'd simply buy a better LED torch - assuming you can afford to do so.

 gravy 24 Sep 2022
In reply to The Potato:

There are so many "it depends" to answer first I be tempted to take Billhook's suggestion! Also one off lenses, even cheap shit moulded plastic condenser lenses are probably of a cost that makes it uneconomic to bother.

So the first "it depends" question is: is it a single LED? how big is it? does it already have a lens (very common bubble of clear plastic moulded into the same package? what is the current angular spread? and finally how far from the LED to the front of the torch?

You cheapest source of lenses will probably be a pair of high dioptre reading glasses but the lens is likely to be too big!

Post edited at 19:41
OP The Potato 25 Sep 2022
In reply to The Potato:

I'm mechanically competent but not about lenses.

Thanks for the replies

 Rob Parsons 25 Sep 2022
In reply to The Potato:

> Ive got a fairly basic LED torch which provides good output, but the beam is quite wide, how do I make it narrower so it projects the light further. Would using a plano convex lens work? im fairly clueless when it comes to optics

A plano-convex lens is converging, so should indeed be what you want. The question would be getting one of the 'right' strength (and of course, the correct physical size.) That might take some playing around with. Maybe if you can get hold of a range of reading glasses to experiment with, that might be a start.

 Hooo 25 Sep 2022
In reply to The Potato:

I have the opposite issue. I have a cheap LED torch that I use for a bike light. It's super bright, but the beam is a bit too narrow. It's easier to spread a beam out than to focus it, but even so, after a bit of fiddling I came to the conclusion that it's massively less hassle to just buy another torch...

If you're interested in a bright torch with a narrow beam I could see if it's still available? It was £9 off eBay c/w a crap 18650 cell (which I replaced).


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