Archive - Feb 4, 2012
Recently, a friend was talking about LED lighting and I spent a little time looking into LED lighting options. Starting at about ten dollars a bulb, you can get LED light bulbs that fit into a standard screw base light bulb socket. These lights use between 6 and 12 watts and are much more efficient than traditional incandescent light bulbs. They are little more efficient than compact fluorescent bulbs, but last much longer without some of the disposal issues.
Yet a lot of the efficiency seems to be lost in trying to get them to behave like traditional light bulbs. Instead, if we used different power sources, we might be able to get much better efficiency. I thought about the Syrcadian Blue light that Kim got me. It runs 25 blue LEDs off of a mini-USB connection. Could better, more efficient lighting be done using USB connections?
So, I started looking around for ideas. The first blog post I found was USB LED Light. It was right along the idea that I was thinking of. It used a 10,000 mcd white LED. The author calculated that putting it together with a 100 ohm resistor would work fine, and he goes through what he did to make it. He notes that with a 100 ohm resistor, the light draws 15.47 mA, well below the 500 mA limit for USB. All nice and good, but what if you want to have more than one LED? What if you use a different LED? How do you calculate the appropriate resistors or the best wiring?
Looking around, I found another blog post, DIY USB LED Keyboard Light. This one used a 5000 mcd orange LED. It went into details about how to know the positive and negative side of an LED, and most importantly, provided a link to a .
The author notes that the voltage range for USD is 4.75-5.3 Volts, and it is best to use 5 volts in the calculator. I did some searching to find some good LEDs to use. SuperBrightLEDs had this listing, a 30 degree 18,000 mcd cool white LED. With a forward voltage of 3.4 votes and continuous Forward Current of 30 mA, I plugged the values into the calculator.
My first pass was to see if I could create something with 25 LEDs, however the calculator came up with an array that would draw 750 mA, 50% higher than recommended for USB. 16 LEDs would take 480 mA, a little close for comfort for my initial calculations. 12 LEDs would take 360 mA. That sounds reasonable. The array of LEDs would draw 1828 mW and would use 12 1/4 watt 56 ohm resistors.
The LEDs are 89 cents each when buying between 10 and 99 LEDs, and it looks like all electronics has the resistors at five cents each when buying a dozen.
I also recently got into a discussion with a friend that was looking buying a chandelier. So, I started thinking, could I take this and build a DIY LED chandelier? Looking on Amazon, I found lots of interesting crystal ball options. You can buy 40 mm crystal balls for $2.72 each. 20 mm for $2.22 each, 50 mm for $6.98 and 70 mm teardrop crystals for $4.54. This would probably be the most expensive part of the project, ranging from $25 to $85 depending on what to use.
The only other part would be the wire, the frame and any other pieces to put this together. So, for around $50 to $100 it may be possible to create a very interesting DIY USB LED chandelier. On the other hand, I suspect it might not give a lot of light. Each LED gives off 4 lumens, so 12 of them would be 48 lumens, It might be good for ambient lighting, but not much else.
What do you think? Does this make sense? Have I missed something or done my calculations wrong? Should I give this a try? Should I try different combinations, like a narrower viewing angle or a different color temperature