Joined: 16 Jun 2004
Posts: 11802
Location: Sydney, NSW
LED lighting fail
I have been working on an idea to replace the regular CFL bulbs in some light fittings with LEDs. The regular bulbs are quite dim and throw a very ugly light pattern on the walls. The idea is to make a large emitter panel that throws an even light that is twice as bright as the CFL. I just finished this:
The panel is 250 x 234 mm and has 150 LEDs. The dark vertical stripes on the edge of the plate are pieces of Kapton tape to insulate the cut ends of the LED strips.
The huge fail is that the strips are already pulling off the aluminium plate, even before I powered the LEDs up . The strips are supposed to have quality 3M adhesive but in places I can see the tape coming off the back of the PCB as well as the aluminium.
To fix this, I can think of two options: buy some *real* 3M VHB tape and re-stick all the strips. The second option is to cut a matching rectangle of 3 mm clear plastic and screw it down over the LEDs to clamp them in place. What do you think, is there a better solution?
Wed Feb 05, 2014 8:20 pm
Jaemus Experienced Roboteer
Joined: 01 Apr 2009
Posts: 2674
Location: NSW
probably the first option, they do generate a fair bit of heat that you probably want not to insulate with plastic clamped over them _________________ <Patrician|Away> what does your robot do, sam
<bovril> it collects data about the surrounding environment, then discards it and drives into walls
Wed Feb 05, 2014 8:31 pm
Nick Experienced Roboteer
Joined: 16 Jun 2004
Posts: 11802
Location: Sydney, NSW
Heat is definitely a worry; the ali plate is there to be a large heatsink for the LEDs. If I add thicker VHB tape, that might be just as bad as as covering the LEDs with a sheet of plastic. If I wire up the strips and then cover half of them with plastic, the thermal camera will quickly show if there is a problem. Thanks for giving me some new ideas!
Wed Feb 05, 2014 9:07 pm
kato
Joined: 11 Dec 2010
Posts: 92
Location: 4505
Would Arctic Silver, or some of the heat sink adhesives or adhesive tape from RS be appropriate?
Thu Feb 06, 2014 6:38 am
Nick Experienced Roboteer
Joined: 16 Jun 2004
Posts: 11802
Location: Sydney, NSW
I will look into that, it depends on how expensive the products are. The individual LEDs are not that powerful and don't need to be treated like 5 watt Cree mega LEDs. I have another 3 panels to build so keeping costs down is important.
Update: I just ran a heat test with half a strip covered and there was absolutely no temperature difference between the covered & uncovered LEDs, so I will go with the no-cost option of scrap acrylic sheet covers.
Thu Feb 06, 2014 8:13 am
Knightrous Site Admin
Joined: 15 Jun 2004
Posts: 8511
Location: NSW
I had similar issues with the LED strips in Farmboy coming off the polycarb, so I just drilled some holes either side of the strips and secured them with a ziptie. _________________ https://www.halfdonethings.com/
Thu Feb 06, 2014 10:28 am
Nick Experienced Roboteer
Joined: 16 Jun 2004
Posts: 11802
Location: Sydney, NSW
The finished panel is working well, this is how it looks:
The white hotspots on the LED strips at about 38 degrees and just happen to be where the strips have unstuck from the aluminium plate. Its using 22 watts of power and if the spec sheet is to be believed, it is putting out 1,425 lumens. That's pretty good, considering that an off-the-shelf Cree 10W LED bulb only puts out around 560 lumens.
Thu Feb 06, 2014 3:16 pm
miles&Jules Experienced Roboteer
Joined: 19 May 2010
Posts: 3973
Location: ipswich QLD
looks pretty damn cool Nick….we bought a fancy led filming light kit and this one looks just as bright.
Amazing stuff them leds.
Now... next version I want to see warm led strips next to these with a mixer to mix daylight colour between them ...and then a dimmer….I know you can do it . _________________ Miles Blow - Julie Pitts
www.mulesfilm.com.au www.wombokforest.com.au
-Pickasso- Vivid Sportsman champion 2015
Thu Feb 06, 2014 4:48 pm
Knightrous Site Admin
Joined: 15 Jun 2004
Posts: 8511
Location: NSW
quote:Originally posted by miles&Jules:
Now... next version I want to see warm led strips next to these with a mixer to mix daylight colour between them ...and then a dimmer….I know you can do it .
Joined: 16 Jun 2004
Posts: 11802
Location: Sydney, NSW
Don't tempt me!
Its difficult to get a good white by mixing RGB LEDs and RGB strips are relatively expensive for the amount of lumens you get out of them, but for mood lighting in a lounge, I would definitely think about it, particularly the addressable strips.
This has gotten me wondering why consumer LED lights are so expensive; I definitely didn't get the best deal on this LED strip and these panels only cost me $34 each while emitting more light than two regular LED bulbs costing at least $60. Those pro photographic LED lights are even more expensive per lumen, although you do get extra features.
@ Miles: have you seen these cheapo lights on-line:
I bought a pair for macro photography and for $28.95 USD, they work really well! They would be plenty bright enough for the sort of video you are doing and appear to be very hackable; I am looking at adding barn-doors and other attachments.
Thu Feb 06, 2014 5:59 pm
miles&Jules Experienced Roboteer
Joined: 19 May 2010
Posts: 3973
Location: ipswich QLD
yeah the possibilities are amazing….and because they don't use much power you could run them off a big ass lipo and it would last for ages. We bought a couple of little ones that go on our cameras to.
I like the idea of building your own custom ones though.
yep those ones look like one of the ones we bought ..but of cause we bought em at a real shop they were at least $100 each... _________________ Miles Blow - Julie Pitts
www.mulesfilm.com.au www.wombokforest.com.au
Those could make for some epic room lights, presuming they don't have a chinese lifespan. _________________ Mechanical engineers build weapons, civil engineers build targets
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