Sylvania Warm White LED C3 Lights

Date: December 2009
Store: Home Depot
Price: $10 (20 cents per LED)
LED Color: warm/soft white
LED Size: 3mm
LED Lens: inverted wedge
LED Count: 50 leds, 2 series strings of 25 leds each
Current limiting resistor: 1 for each string of 25 leds, 1200 ohms (??). Includes a reverse current protection diode.
Rectification: half wave using the LEDs as the rectification diode.
Bulb lead material: steel, subject to rust
Power: 4.8 watts

Notes:

The plastic C3 diffuser on these bulbs is interchangable with other Sylvania and Phillips LED strings. It is not interchangable with GE light strings. These diffusers work particularly well with the pink LED string from Phillips. The diffusers that come with the Phillips pink string look crappy but with the diffusers from this string they're very nice.

This is only a half-wave rectified set. That means the bulbs flicker on and off 60 times per second, offering light only about 30% of the time. The polarity of each of the 25-led strings is reversed, so 25 leds light on one half of the wave and 25 light on the other.

The oscilloscope offers both good and bad news. The good news is that there's no perceptible reverse voltage across the LED (right) and the the top of the wave form is nice and flat. The bad news is that it looks like Sylvania may be driving the LEDs with too much current.

The voltage measurement over the resistor (left) tells a similar story with the voltage spiking to 75 volts at the peak of the sine wave. Nice smooth pattern but much higher than expected. As expected from this graph, the resistor pack gets quite hot.

Compare this reading with the GE set.

After filling the sockets with dielectric grease, I used one of these sets to replace the light for the awning over my front door. We'll see how long it lasts. [Followup November 2010: I replaced one burnt out bulb. It burnt closed (current flowed) so I didn't have to hunt for it. So, it has been satisfactory and the dielctric grease did its job of preventing rust. If I had it to do over, I think I would start with an Ecosmart set instead.]

I used another set as accent lighting for a painting. [Update November 2010: no burnouts yet.]