The dimmable bulbs incorporate silicon-based Infineon or ST power transistors. We did not find silicon carbide technology in any of the lamps.
Each lamp uses a different LED driver IC. Pharox uses four ICs, 40 resistors and 16 capacitors, plus transformers and many diodes. All this to dim a 40-W-equivalent light bulb—but only, in some cases, if you purchase a new dimmer, since your old dimmer might not be compatible.
Philips uses a remote phosphor, relying on the bulb envelope material to do the wavelength conversion. Lutetium oxide is used as a fluorescent medium in more than one lamp. We have looked at many LEDs over the last few years and have never seen lutetium used before. More conventional phosphors, such as barium and cerium-doped YAG (yttrium aluminum garnet), are also seen, along with a cocktail of rare earths such as europium and strontium.
Surprisingly, everyone uses blue GaN LEDs—no RGB LEDs in this lot. There are red LEDs in the Pharox, complete with lenses, but they don’t turn on when the lamp is on. They are obviously not for color balance. Maybe the light turns red when the bulb is about to die, or to signal that the lamp is not wired properly.
Philips uses many of its own Luxeon Rebel LEDs in a modular arrangement that could possibly permit the replacement of failed modules. We expected the Sylvania to use an Osram LED, perhaps a Dragon, but that is not the case. Two of the lamps rely on Cree dice.
The LED light-emitting area varies from 4 mm2 to 12 mm2 for the 40-W equivalent bulbs—a variance of a factor of 3—yet their power consumption ranges between 6 and 9 W. Some have four LED dice; others have 48.
Click on image to enlarge.
At what point is such a lamp considered to have reached the end of its operable life, given its dozens of individual LEDs? Nowhere on the fancy packaging, with all its warnings, disclaimers and warranties, is there a definition of the point of final failure for the lamp. Will it go out with a flash? Will it still be usable for its intended purpose until the last second, or will there be a point at which the light has become so faint that the user decides to replace the bulb?
Lots of questions, and we still haven’t answered the first one: Why are A19 LED bulbs so expensive? At 50 to 60 lumens/W, the LED bulbs have the same efficacy as 40-W-equivalent compact fluorescent lights, which typically offer 560 lumens at 10 W, can be purchased for a few dollars and should last, or so the packaging claims, up to eight years. For the same savings in electricity as you’d get with a single LED bulb, you would need to purchase two or three additional CFL bulbs over the next 25 years. Luckily they are available in packs of two or four.
Light bulbs are a commodity item, no matter how long they last. For all the claims of CFL longevity, I have yet to see them reach their expected lifetime. Usually the point of CFL failure is the electronics in the neck, and the same will likely hold true for LED bulbs.
With CFLs, however, we have traded energy consumption for mercury contamination. The attraction of LED bulbs is twofold: They are instant-on, and they are mercury free. The toxicity of rare earths is low, and very little of the material is used in the bulbs anyway.
Over time, LED bulbs will drop in price and will provide a cleaner, safer alternative to CFLs—presumably with a longer life expectancy as well. We can also expect new features; the door is fully open on that front.
About the author
Martine Simard-Normandin is president and CEO of MuAnalysis Inc. (Ottawa), a privately owned professional laboratory.