General Electric LED Energy Smart Lights

Store: K-Mart $12 (November 2010)
Store: Sears $12 (November 2010)
Store: Lowes $8.40 (December 2010)
LED Color: warm/soft white
LED Size: 3mm
LED Lens: dome
LED Count: 50 leds. 1 series string of 25 sets of 2 parallel LEDs
Current limiting resistor: on each end embedded in the plug
Rectification: full wave using diodes in each plug.
Lead material: steel, subject to rust
Power: 3.2 watts

Also seen: Home Depot November 2010 as Martha Stewart Living

Notes:

This was the only full-wave rectified set I found at the local stores in 2009. Because it uses both halves of the AC sine wave, the lights are lit 60% of the time instead of 30% like a half-wave set. This also means that they flicker at 120 Hz. Unlike the 60Hz flicker of a half-wave set, the 120Hz flicker is imperceptable to the human eye. The lights appear solidly lit.

The diodes for full wave rectification and the current limiting resistors are embedded in the plugs at either end of the string. As a result the plugs are much larger than with other sets.

This set has a novel feature: individual LEDs can burn out without causing the rest of the string to go dark. Every two bulbs are wired in parallel (see picture). As long as both adjacent bulbs don't go bad, the string will remain lit.

Measured on an oscilloscope, the rectified voltage across a parallel pair of LEDs has a nice flat top to it and the peak voltages is only 3.25 volts with a peak current of around 15mA. The low current (below the recommended 20 mA) makes them less bright than comparable sets but it should also make them more reliable. If a bulb does burn out, the remaining bulb in the pair is driven at a peak current of 30 mA. This is still less than the typical peak current of 40mA in a half-wave sets.

As you might expect from the 3.2 watt rating, the bulbs in this set appear about 30% dimmer than the 4.8 watt half-wave sets. They'll look great on a christmas tree but if you want to experiment with LEDs as direct illumination, start with the generic Target set instead.

Also seen: Martha Stewart Living
Store: Home Depot
Date: November 2010
Price: $10 ($2 less than K-Mart/Sears)

The box is exactly the same shape and size as the GE set and contains exactly the same cardboard and plastic pieces and exactly the same lights. The only difference is the color of the box and the price: Home depot has them for a few bucks less.