Megalamp, the return

The project: Megalamp Mark III scuderia Sti. After my experience with the mark II: specifically lots of light, but the occasional piece falling off, I decided to make a new light. The idea was to make a water resistant, durable Lithium driven light that would use the excellent TaskLed Hipflex driver. Oh yeah, and while I was at it, I wanted something a lot brighter -- why not, right? So: machined Al housing, 14.8 V lithium pack, triple Cree MC-E, Reflector optics. I had been thinking about this for a while, but my bike commute on an unlit bike lane brought it back to the forefront.


housing: A very generous machinist made the housing out of Aluminum based on my specifications. I mocked up a model in Sketchup, but he went a step further and took my measurements and put it into SolidWorks and cranked the thing out.


Next, someone suggested anodizing, which I did:




optics: The choices for small optics for the MC-E that work well are a bit limited, but the Ledil Booms seemed like a reasonable choice. I haven't used reflector based optics because I didn't want to deal with a protective covering, but my lab contact generously made me a polycarbonate lens, so why not?!


output: Here are the Cree numbers for the MC-E for K bin: 370-430 lumens at 350 mA. Looking at their graph, it looks like you can get up to ~173% of the 350 mA light at 700 mA. IF you could run three MC-Es at 700 mA (like running 12 individual LEDs at this current), you would be making ~1920-2230 lumens! I plan on running at 350 mA to preserve battery and not damage things, so I can expect a paltry 1110-1290 lumens. This is ignoring optics, efficiency of the driver etc, so take it with a big grain of salt. Even with the salt, though, it's very bright, and when you consider the price of the parts (excluding the fancy case), it works out to be quite cehap compared to the 900 lumen $700 lights on the market.

Here are theoretical values, assuming 370-430 lumens for the K bin:

mA watts lumens
1000 9.3 833-976
1400 13.4 1110-1290
2000 20.4 1499-1742
2400 24.5 1721-2000
2800 29.4 1920-2231

not sure about the watt values, since I didn't take much time in my reading of Vfs off of the Cree datasheet. In normal operation I will be dimmed quite a bit, I think. I'll try 1400 mA to start with.


Temperature: At 50 degrees C, you lose ~ 6-7 % intensity, 75 degrees, 12-13%, 100 degrees, 18 %, so here's hoping all that Al dissipates the heat. Thankfully there is a temperature sensor built into the Hipflex. The other concern is decreased lifetime of the LEDs.

weight: 215 grams for the light + wire
247 grams for the battery + wire + case = lighter than the seca 900 by a lot.