DIY 115 watt flexible LED Task Lamp

 

ledtask_headSo I wanted a very bright flexible LED task Lamp that didn’t break the budget. I had a few feet of 7020 LED strip lighting left over from my undershelf LED lights, so I decided to put those to the task. These LEDs give off about 33-35 lumen per LED, and I’m using 54 LEDs for the task. That’s about 1836 lumen which translates to roughly 115 watts of light. The best part is that it’s very efficient, only using under 20 watts of power, including power supply losses, measured by kill-a-watt.

Shopping list:

  • 120mm x 100mm x 18mm Heat Sink: The mounting base for the LEDs is an aluminum heat sink. All these LEDs give off a bunch of heat in a small space, so a heat sink is crucial. While I could have done the thermal calculations to determine exactly which heat sink to buy, I had a hard time even finding a suitable size and shape of heat sink I wanted, that could be delivered in a reasonable time frame. $12 prime-shipped.
  • The 7020 LED strip lights from ebay and China: These things are freakin’ awesome. Really bright, really easy to use. You power them with +12v using a regular off the shelf adapter. The LEDs feature a positive and negative rail that runs down the length of the super flexible PCB. They include adhesive on the back. $23 for (16) feet of the stuff shipped from China, via the slow boat, seriously.
  • 18″ flexible gooseneck and desk clamp: I could have ordered a 24″ for just about the same price, and I think that would have been the better choice. This gooseneck is really high quality and the stiffness makes me think it will last a long time before I need to replace it. This is NOT the cheap quality stuff you get on IKEA/Walmart/Target lamps. This company’s website is a little hokey and my order errored out the first time I placed it. About $32 plus shipping is fixed around $13 for the two items, which is sort of ridic, but whatever. The most expensive part of the lamp.
  • A cheap 12v power supply: Provides +12v at 5 amp which is more than enough. This lamp only draws about 1.3 amps, so you could get something smaller. $8 prime-shipped.

 Installation Notes:

  • Notice that there is a positive and negative rail that runs lengthwise down the strip. On one side, notice that I cut the negative rail short, and on the other side, I cut the positive rail short. This is so I could run my own power bus straight down and connect all the strips together. +12v rail on one side, GND on the other.
  • Both the center of the strips and the edges are insulated off of the aluminum heat sink. While there is some separation with the adhesive, I wanted to make sure this stuff didn’t short!
  • I used a smaller stranded wire (24 gauge) to connect the strips but only for 6 or 7 inches. I convert quickly to 18 gauge which should be much more sufficient.
  • I used heat shrink tubing extensively to add better protection for the wires.
  • I drilled a 3/8″ hole in the bottom of the heatsink to mount the gooseneck. The gooseneck didn’t have much metal to “grab” so I used two different JBWELD products. Their stuff is awesome. I used SteelStik (soft, flexible, steel-fiber, epoxy putty) to form a top cap. I also used their ClearWeld at the base of heatsink which rests on the top lip of the gooseneck. Is this overkill? Probably. Will this connection break in my lifetime, almost certainly not! See pictures below.
  • I added an inline switch to the AC side of the power supply figure-8 cable.
  • These LEDs are on the blue end of the spectrum and produce a very very white light. This is completely different from Incandescent light, and you if you photograph under it, make sure to adjust your white balance accordingly.
  • I’ve made a huge leap of faith with this heat sink. I could be entirely underestimating the amount of heat dissipation required. I can tell you that after an hour of running, some parts of the LEDs are close to their maximum operating temperature(170F), while the rear of the heatsink (average temperature) is around 85F. The fins are much hotter.

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About the author

keith

Amateur Electronics Design Engineer and Hacker

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