In February 2010, EDN tore down its first LED bulb (Reference 1). For $20, you got a non-dimmable bulb that produced 500 lumens at a cool white (5000K) and consumed 7W. The warm-white version of the light produced only 450 lumens. Two years later, you can buy this fully dimmable Samsung bulb for $19.95 (list price) that puts out 550 lumens of a nice warm white (3000K), consumes 10W, and boasts a five-year warranty.
1. As you’d expect with a snow-cone-type bulb, the light pattern does not extend as far down as the light extension of an incandescent bulb (Reference 2).
2. The light uses only one LED component to produce its 550 lumens.
3. Lights that are not incandescent face a challenge when you try to control them with an old-fashioned TRIAC-based dimmer switch. The graph below shows the dimming characteristics of LED, compact-fluorescent, and incandescent bulbs, showing their dimming performance as a percentage of their highest light output, rather than an absolute measure—say, in lux. The incandescent bulb (yellow line) does not dim linearly with power. It does dim down to zero, however. A CFL (orange line) does a better job of dimming with power, and the Samsung LED light (green line) dims linearly with power. However, it drops out at slightly less than 20% of its maximum output light. I used a Taos light sensor from Adafruit, controlled by an Arduino development system, to take these measurements (Reference 3).
4. It’s usually difficult to find out what power-management IC an LED bulb uses, and this one was no exception. By process of elimination, it seemed likely that the IC must be beneath the white blob of goo.
5. Sure enough, the vertically mounted IC shows a Power Integrations logo and a LinkSwitch part number: LNK403EG (Reference 4).
6. All of the electrolytic capacitors used are 125°C and most likely are properly derated, contributing to the manufacturer’s five-year warranty. The bulb’s packaging lists a design life of 40,000 hours.
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