LED bench lighting the hard way - Page 1
Forum section: electronics / projects

author: dmmt40
author_rank: Regular Contributor
timestamp: February 21, 2016, 07:11:06 pm
content: Hello, just wanted to share a small project I've been working in the past couple of days for lighting a workbench.What I decided to do is to use several high power led emitters with a lens/reflector to aim the light exactly where is needed, instead of the more common approach of using a led strip.LEDS:The leds I used are Cree's XM-L2http://www.cree.com/~/media/Files/Cree/LED-Components-and-Modules/XLamp/Data-and-Binning/XLampXML2.pdfI'm using six connected in series. The reason I went for these is becausea) They're very brightb) Very efficientc) Lots of options in lensesd) Readily available.Color temperature is 2700k, some people think it's too yellow/orange but I like itConstant current driver:The driver used is the Recom RACD60-2500Ahttp://www.recom-power.com/pdf/Lightline/RACD60-A.pdfA bit expensive but has a couple of nice features: dimming can be very easily controlled with just a single 100k pot, so hooking it up is quite simple, also instead of using PWM to change the brightness of the leds, it varies the constant current output, as the datasheet says it goes from 250mA to 2.5A this is good because it avoids flickering which I find really annoying and also prevents excessive noise coupling into a circuit I might be working on.Cooling:This was probably the most tricky part, because unless you physically connect and measure the leds there's really no way to know if a heatsink of a specific size will be sufficient. So I prepared for the worst and got a CPU cooler, which then I drilled and tapped M3 size holes.Reflectors:The main reason I choose single leds instead of a led strip is the ability to fit a lens or reflector and make the whole installation much more efficient. At first I thought of getting a straight lens and tilt the complete heatsink assembly a couple of degrees to point them to the front of the table, but looking around I found these angled or "asymmetric" reflectors from LEDiL:http://www.ledil.com/node/2/p/8603?ds=1&mn=0&ld=290&md=0&xd=0&mh=0&xh=0&mt=0&mf=0&xf=0&sf=0&fm=0&ty=0&sm=0&cn=0&vc=0&io=0&tro=0&tpo=0&tr=n0&tp=n0&trt=0&tpt=0&fr=n0&st=0&pg=1&lo=n0&ol=0&of=0&od=0&oh=0Normally used in museums for art installations, they point the light at around 30deg off axis but are mounted horizontally on the heatsink. Pointing them at the wall you can see they work just as advertised:Final measurements:30% brightness 823lux.I found this to be a very nice level for general purpose work, like soldering trough hole components, reading etc This is how it's set 90% of the time and power consumption is super low, the leds drop 17.52V @750mA, taking into account driver efficiency total power draw is 15.8W that's almost 3 times brighter than a 40W bulb for 38% of the power and across the whole bench too, not just in a little corner.Increasing the brightness to 50% we get 1328 lux, this works very well for taking pictures or video, also it's great for soldering and assembling small SMD components. Voltage drop is 18.24V @1.25A total power: 27.5WAnd finally at the driver's full current the reading is 232 x10 = 2320 lux.The only use I can think of is if I need extra light during the day when the windows are open and there's already plenty of light. Voltage drop: 19.38V @2.5A total power: 58.4WBy the way I did take a reading before fitting the reflectors in the exact same conditions and I got half the brightness in both 50% and 100% dimming, so if you consider using high power leds I highly recommend a lens or at least a reflector, it makes a huge difference.And now what everyone wants to know, how much for all of it? Here's a breakdown on the components:6 Cree XM-L2 leds $27.56 CPU heatsinks $306 Asymmetrical refelectors $16.5Constant current Led driver $45Total: $119So there you go obviously a bit on the expensive side but for this much light it's worth it. Having said that though, if I ever need to install another set of leds under a cabinet or something I would probably use smaller and cheaper Leds like Cree's XPG series which in turn allows for a smaller driver, I can probably get the price down to $80 and still get half the maximum brightness, but having this much headroom is really nice plus the leds will have a much longer life since they will always be cool and driven at reasonable currents.Dan

author: mmagin
author_rank: Frequent Contributor
timestamp: February 22, 2016, 12:48:52 am
content: Yeah, I like the efficacy and CRI you can get when buying name-brand COB emitters.I have a little worklight attached to my Hakko solder-fume filter made from a Recom RACD06-30 and two Cree CXA1304 emitters in series epoxied to a random surplus heatsink. The power supply is just screwed to the back of the heatsink (it doesn't run very hot) and a cord is attached.

author: dmmt40
author_rank: Regular Contributor
timestamp: February 22, 2016, 04:02:16 am
content: You're right they look pretty nice, of course I also could've gotten cheaper leds and driver but since I use this every day for several hours I didn't want to skimp on the components, it will pay for itself in the long term I reckon.

author: tino_so
author_rank: Contributor
timestamp: February 22, 2016, 04:09:25 am
content: Very nice results! Thanks for sharing the b.o.m, I have a similar project on my to do list. My current lighting is a nuisance when I am soldering small components and the glare on the tablet and off some bench gear can be awful. An arrangement similar to the one you installed could greatly reduce my problems.

author: nasteban
author_rank: Newbie
timestamp: February 22, 2016, 05:58:08 am
content: I really enjoyed your project post, dmmt40. It was nice to read a little bit of back-story to go along with the construction details and the bom. The pictures of the installation and the results were also great.

author: GamerAndds
author_rank: Regular Contributor
timestamp: February 23, 2016, 07:07:24 pm
content: Awesome! How long was this whole thing?

author: dmmt40
author_rank: Regular Contributor
timestamp: February 24, 2016, 03:11:36 am
content: Hello GamerAndds, I asume you meant "how longisthis whole thing" (haven't taken it down yet and don't plan to) from the first to the last led it's 1 meter, the 6 leds are 20cm apart. The illuminated area in the table is 140x50cm