How to mitigate a light pipe thats too short - Page 1
Forum section: electronics / general

author: skyjumper
author_rank: Regular Contributor
timestamp: May 16, 2020, 03:14:07 am
content: Hi All... I have designed a standard, 2 layer (components on one side) PCB and there is a standard enclosure it can fit in, with some machining. If I can make this work it will be much cheaper than a custom enclosure (even a no molds one) but the only issue is finding a rigid light pipe thats the right length. I need one that's ~23.5mm, but the closest I can find is 19mm.I'm wondering is anyone has tried lengthening a rigid light pipe with some plastic tube or some other scheme?I looked at using a flexible light pipe, but this is a low quantity device with 4 LEDs, so that would add nearly $7 (US) to each unit.Any ideas?Thanks...

author: I wanted a rude username
author_rank: Frequent Contributor
timestamp: May 16, 2020, 04:24:04 am
content: Have you tried setting up a light pipe ~5 mm from your LED to see how it looks? Hypothetically it should work, albeit with a substantial reduction in brightness.If the problem is holding the light pipe in place, there's always epoxy ...

author: ebastler
author_rank: Super Contributor
timestamp: May 16, 2020, 06:20:32 am
content: You didn't describe the geometry you are after, but would something like this work? These look like the are 25mm long, and the actual light guide can probably be trimmed to size on the LED side. In stock at Mouser for 90 cents or so (qty 100); maybe you can get a better price elsewhere.https://www.mouser.de/ProductDetail/Bivar/LPV2-1000FP?qs=F5EMLAvA7IBFOiMv7hecGA%3D%3Dhttps://www.mouser.de/datasheet/2/50/Bivar-05-28-2019-LPV2-XXXXX-XXX-1596629.pdf

author: skyjumper
author_rank: Regular Contributor
timestamp: May 16, 2020, 09:41:02 pm
content: Thanks guys. If the pipe is a few mm above the LED it gets dim quick. I tried trimming light pipes, they shattered. I'm going to experiment with some plastic, black tubing and see if that helps. The pipe may still look dim at the top but hopegully less dim and maybe it will prevent the colors from the different LEDs from bleeding over.

author: pisoiu
author_rank: Regular Contributor
timestamp: May 17, 2020, 08:21:26 am
content: It dims quick perhaps because you are using a wide angle led. If possible, try to replace it with a narrow angle, so that all the flux is projected on the pipe end.

author: skyjumper
author_rank: Regular Contributor
timestamp: May 18, 2020, 09:11:57 pm
content: It actually is a narrow angle LED, but I may have found the solution. I can probably raise the PCB up in the enclosure by slipping some nylon washers under the board and using slightly longer mounting screws. The machining for the enclosure has not been designed yet, so I think this will resolve the issue. It makes assembly just a little bit more annoying but its a low volume run, and now I can still use the 30 cent light pipes.

author: David Hess
author_rank: Super Contributor
timestamp: May 19, 2020, 01:02:34 am
content: Quote from: skyjumper on May 16, 2020, 03:14:07 amIf you have a suitable cement, then a length of clear polystyrene can be used to extend the light pipe. Alternatively heat shrink tubing can be used to join a section of clear polystyrene but this is mechanically questionable.