These E14 bulbs can be bought on eBay or Asian sites for less than 5 euro each with shipping included. Since I was curious about how the current was supplied to the LEDs I decided to disassemble one of them.
This is the bulb in question, it has an E14 base and is very similar in shape and size to a candle shaped incandescent bulb:
This is the bulb without the diffuser glass, the glass top is glued to the heat sink with silicone (or a similar substance):
The bulb is rated at 3W, so it’s probably safe to assume these are 1W LEDs.
The base of the bulb is screwed to the aluminium heatsink and it’s easy to disassemble:
Then I unsoldered the wires from the LED board, this how the inside of the heat sink looks like:
The controller was protected by heat shrink tubing, this is the controller with the protection removed:
And the bottom of the PCB:
This is the top of the controller with the capacitor lifted:
The IC is labeled 3706M and the layout of the board suggests that it’s either a BCD AP3706 or an equivalent, since the board layout is very similar to the datasheet’s “Typical Application” section.
The top transistor is labeled 13003 and should be similar to ST’s STX13003.
After looking at the board I took some measurements. My AC mains was steady at 230V and the current draw was 15,4mA. At the output of the controller the voltage was 9,67V and the current draw of the LEDs was 313mA, this suggests the LEDs were getting 3.03W, so it’s dead on the rating, at the mains side the overall power was 3,54W, this means the energy wasted by the LED driver could be lower, but still making this bulb energy efficient.
At this price level I was actually expecting a simple capacitive transformerless power supply, but the LED Driver appears to be pretty well made. I don’t know how it would cope with high humidity locations, but for regular indoor situations I expect these to last long.
There is one minor problem, the 3 LEDs are wired in series, that means if one fails the others will go dark too.
Now some buying tips and color comparisons.
There are lots of suppliers selling these bulbs but they are not similar, even if they look the same, and the most significant difference is the color temperature. This disassembled bulb is part of a pair that I really don’t like because the color is greenish, but I also bought bulbs looking exactly the same (and also “warm white”) from a different supplier with very good color.
These comparisons were made with a white paper as a background and shot with 55mm lens set to F/4 on a Canon 550D manually set to ISO100, 1/80 sec. exposure and the white balance set to “White fluorescent”.
This is the comparison of those 2 bulbs, the disassembled bulb on the right and the one I prefer on the left:
Even the light output is similar, the only difference is the LED quality.
This is the greenish bulb compared to an halogen bulb (Philips EcoClassic 20W):
And the same halogen lamp compared to the “good” warm white LED:
The color temperature is very pleasant.
This is the “good” warm white compared to a Luxram branded 11W 4000K CFL (3min warmup):
This is the same “good” warm white compared to a Digilamp branded 15W 6400K CFL (3min warmup):
In a hall with lights turned on by a movement sensor that was initially lit by four incandescent bulbs the power consumption was considerable, when these incandescent bulbs were replaced by CFLs the bulbs kept dying very shortly because of the several daily starts. Now the CFLs were replaced by these cheap LED bulbs and they are still going, after more than six months. The four 3W LED bulbs don’t have the light output of the 4 incandescents but are still adequate.
I now believe that the way to go is to buy samples from a couple of cheap suppliers and then buy the rest from the supplier with the best samples. The problem with these cheap LEDs is that after several months the same supplier might be selling the same bulbs but with slight differences in color, but that might also happen with CFLs.
I now plan to buy 6 decent single LEDs and replace the emitters in the 2 greenish bulbs I have, then I want to compare the efficiency of these cheap bulbs with the more expensive ones from brands like Philips. In locations where the bulbs are started several times per day and there is no need for great light output these are starting to look a lot better than CFLs.