Solar Powered LED Holiday Lights Update

I picked up a 50-LED white string of solar powered "Solar Santa Lights" from the Herrington Catalog store ( http://www.herringtoncatalog.com/h718.html ) which appear to be very similar to these. The claim is that they are solar-powered lights in various configurations of 50 white, 100 white, or 50 multi-colored bulbs.

I don't know if it's really worth $30, but it's a neat thing to tinker with. The lights can be set to be on steady or blinking (about 20% duty cycle 2Hz flash). The solar panel is made of 4 polycrystalline segments about 1.5" x 2" total. The top looks remarkably similar to those for the LED path lights in size and shape.

For a battery, it uses a single 600mAH 1.2V AA NiCD cell that is user-replaceable through a battery door. I checked current consumption and my cheap DMM reported 30mA. Suspecting some kind of step-up DC-DC converter, I checked it with a 1-ohm resistor on an oscilloscope, and it actually draws a 60KHz triangle wave that's 140mV peak-to-peak. Average current, therefore, is about 70mA. Thus, the 600mAH battery should last around 8 hours.

Total power draw is only 84mW or so, giving each LED a maximum of about 1.5 mW of power -- as if driving a 3V white LED with 0.5 mA of current or about 2.5% of typical maximum brightness. Each LED appears to be wired in parallel. They have clear cylindrical optics with an inverted cone opposite the emitter. This makes for a 360-degree visibility pattern. And although each outputs a measly 1.5 mW of energy, the lights are easily visible in shaded daylight.

When exposed to a 500W halogen lamp at a few inches, the battery charges at 300mA, so it can be fully charged with just 2 good hours of sunlight.

Taking it apart, it appears that the solar cell is wired to the battery with a diode. The light sensor drives a transistor to activate the main circuit. There didn't appear to be any inductors, but several capacitors and transistors that are arranged as in a configuration that -- at cursory glance -- appeared to be a voltage multiplier.