Diffusing Power LEDs - Page 1
Forum section: electronics / projects

author: steve30
author_rank: Frequent Contributor
timestamp: April 11, 2013, 07:32:17 am
content: My little electronics lab is built under a bed and hence has pretty poor lighting. Seehttp://mjlorton.com/forum/index.php?topic=94.0for a picture.I would like to use LED lighting on the bench. I have installed a nice Luxeon K module with 4 emitters and a colour temperature of 4000K and a CRI of about 80. This is a very nice light, but it really needs diffusing. Currently, the bench has an 8W T5 tube which is nicely diffused (but is pretty rubbish light).Would just a piece of diffused acrylic placed a suitable distance below the LED do? Alternatively I guess the LEDs could point up and reflect off a white surface, provided I can find something reflective enough (any suggestions?).Just want to make sure I'm not missing anything that ought to be obvious.

author: Psi
author_rank: Super Contributor
timestamp: April 11, 2013, 10:30:24 am
content: You can use sandpaper on some LED to make them diffuse.If you happen to have a dead dataprojector in your junk draw they have a few nice low-loss diffusers inside.

author: steve30
author_rank: Frequent Contributor
timestamp: April 11, 2013, 10:53:51 am
content: Sadly I've no dead data projectors.Sanding would probably do, but I'm not too keen on doing that on an expensive small power LED.

author: HackedFridgeMagnet
author_rank: Super Contributor
timestamp: April 11, 2013, 10:58:05 am
content: I have had the diffusion problem with LED lights I have made, and I consider it to be one of my biggest problems. You get dazzled by the little pinpricks of light and it can't be good for your eyes.Reflecting back off white surfaces works great from roomlighting and is apparently very efficient. I also makes a beautiful light in the room, but you need a lot of light as you have to light up the whole room.Doug from Analog design has an interesting light for sale, I bought one and it too creates pleasantly diffused light.I am using Cree XPG LEDS.I found one layer of prismatic perspex to be ugly and not diffuse enough, but it is ok for the lab and garage. Just don't look at it.I found one layer of prismatic glass to be beautiful and but not diffuse enough. It dazzles you quite a bit.I put one layer of prismatic glass and one layer of prismatic perspex back to back it was nicely diffuse but lost the nice way the glass sparkled when it was turned off.I am thinking of one layer of slightly lossy diffuser (cloudy) and then the glass, but haven't tried it.

author: Psi
author_rank: Super Contributor
timestamp: April 11, 2013, 11:13:00 am
content: I have a sheet of sanded aryclic on my led room lighting.It's not perfect though, you can still see the leds though it.Ideally you want a diffuser that's made from 100's of tiny lenses followed by a layer of aryclic or similar.

author: notsob
author_rank: Frequent Contributor
timestamp: April 11, 2013, 11:18:08 am
content: Have you tried diffuser sheethttps://www.inventables.com/technologies/light-diffuser-films

author: croberts
author_rank: Regular Contributor
timestamp: April 11, 2013, 11:37:57 am
content: I use prismatic drop ceiling panels for the LED lights in my home lighting system. I cut the round and custom shapes from the standard 2' x 4' panels. Some photos are attached.

author: steve30
author_rank: Frequent Contributor
timestamp: April 11, 2013, 12:08:55 pm
content: Thanks for the posts everyone.I think I'll buy some plain acrylic sheets and some prismatic sheets and have a play with them and see what I can come up with.The diffuser stuff on the inventables site also looks cool. Has anyone here used it?HackedFridgeMagnet: What light did you buy from Doug? Got a link/pic?

author: HackedFridgeMagnet
author_rank: Super Contributor
timestamp: April 11, 2013, 12:17:27 pm
content: Not just pictures, got three videos.They are the same ones that Dave put up in his new lab, he did videos about it. episodes #361,362,364I choose the warmest colour, I find it a bit yellow, but most people who see it, comment on it and say they like it.

author: croberts
author_rank: Regular Contributor
timestamp: April 11, 2013, 12:19:25 pm
content: The panels I use are Acrylic Lighting Panels Prismatic White (23.75" x 47.75") made by PLASKOLITE,INCwww.plaskolite.com. No item number on the label but the number on the bar code is 0 74507 99213 7.

author: StevenB
author_rank: Contributor
timestamp: April 11, 2013, 12:24:59 pm
content: I've used wax paper with good luck diffusing power LEDs. In one application, I used a PVC pipe with the LEDs on one end, cellophane wrap in the middle, and wax paper on the other end. I was doing color mixing, but I would think it would work for ambient lighting as well (you could probably do away with the cellophane). I imagine efficiency is greatly compromised. I'm not sure how fire-safe this is either.

author: steve30
author_rank: Frequent Contributor
timestamp: April 11, 2013, 12:36:41 pm
content: Quote from: HackedFridgeMagnet on April 11, 2013, 12:17:27 pmA ha. I watched those Doug Ford videos with great interest and those LED panels really do look nice.

author: ee851
author_rank: Regular Contributor
timestamp: April 11, 2013, 08:12:02 pm
content: Quote from: steve30 on April 11, 2013, 07:32:17 amThat's a good idea. You could take a sheet of white poster board and use it as a reflector. Bend it into the shape of a parabolic trough--its cross section a parabola--and place the LED at the focus of the parabola, pointed at the trough. Don't get it so close to the paper the paper will catch fire. You'll have to figure out:(1) How to hold the paper in the parabolic trough shape.(2) How long to make the trough to reflect most of the LED's luminous output.

author: G7PSK
author_rank: Super Contributor
timestamp: April 11, 2013, 09:03:17 pm
content: Do you have an old laptop or flat monitor screen to break up as they have a diffuser sheet in them or at least all the one I have taken apart did.

author: NiHaoMike
author_rank: Super Contributor
timestamp: April 12, 2013, 01:37:43 am
content: Just bounce the light off the wall.

author: TerraHertz
author_rank: Super Contributor
timestamp: April 12, 2013, 03:35:00 am
content: Quote from: G7PSK on April 11, 2013, 09:03:17 pmThis. I was just about to post the same. EVERY single dead LCD screen I've pulled apart had a nice diffuser sheet in it. There's typically a sheet of clear plastic a few mm thick, that the side lighting (LEDs or CCFL) shines into the edge of. That sheet will have little squares of white paint distributed on the rear surface, in a pattern that results in an average even 'loss' of light from the total internal reflection in the clear sheet. The light bounced off those goes forward, but is still a pattern of dots. In front of that, there's a very thin diffuser sheet; looks like frosted glass but flexible. After that the light distribution is even, and then passes through the LCD polarizer-gate-polarizer sandwich.I have kind of an opposite problem. I'd like to take the light from an array of RGB LEDs, and reduce it down to a point source so it could then be passed through a lens system to get a variable focused narrow beam, or wide beam.The problem is to do it in a short length.

author: Things
author_rank: Regular Contributor
timestamp: April 12, 2013, 03:35:25 am
content: Strip of baking paper over the LED's should do the trick. Cheap, easy, and almost everyone has it around the house. Not the best looking, but it works.

author: steve30
author_rank: Frequent Contributor
timestamp: April 12, 2013, 08:57:09 am
content: I do have a couple of scrap LCD parts lying around somewhere, and there is definitely some diffusing stuff. I'll try that.Thanks for the suggestions everyone.