I got hold of LED Lighting: A Primer to Lighting the Future and learned a bunch of stuff that I didn’t know about LED light bulbs.
Many of the bulbs sold are not lighting the room via LED. The LED blasts a phosphor with a harsh narrow spectrum of (fairly blue) radiation and then the phosphor re-radiates a broader spectrum. Partly this is because the phosphor radiates more broadly than an LED and partly this is because it enables all of the electricity-to-light conversion to be done by a blue LED. A blue LED is about 30 percent more efficient than an LED of a redder color. The warmer the bulb desired, the less efficient it will be, due to the fact that more red phosphor must be used and the photons coming out of the red phosphor don’t have as much energy as those from yellow phosphor.
LED bulbs are not especially energy-efficient. They produce approximately 50 lumens/watt, which is the same as compact fluorescent bulbs.
The traditional color rendering index (CRI) to measure the extent to which a bulb puts out a broad spectrum of color is being replaced by Color Quality Scale (CQS). To some extent, this new standard is intended to make LED bulbs measure better.
Haitz’s Law says that every 10 years we are supposed to have a 10x drop in cost-per-lumen and a 20x increase in light from an LED. It is unclear how much more efficiency can be wrung from LED bulbs. This article says that someone the laws of physics have been bent by an LED in a lab at MIT, with more light output than energy in. Other sources say that LEDs are already about 80-percent efficient.
LED bulbs depend critically upon heat sink design. The bulbs don’t radiate waste energy in the form of infrared light so any inefficiency needs to be dealt with by a heat sink especially due to the fact that if the LED gets hot it will produce less light. On the other side of the spectrum, LEDs don’t put out ultraviolet light either and therefore supposedly don’t attract insects.
Household wiring is incompatible with LED bulbs in two ways: the voltage is way too high; the voltage potential rises and falls 60 times per second. LEDs operate at lower voltages and have almost no persistence, i.e., when you take the voltage away the light goes off instantaneously. In order to bring the voltage down and turn the alternating current (AC) into direct current (DC), an LED light bulb is crammed with electronics. Therefore it might not be that much more expensive to add IP-addressability and have all of a house’s light bulbs on the WiFi network.
[I’m not sure if I recommend this O’Reilly book, by the way. The author makes no attempt to explain what an LED is. I’ve found this with most books on technology written for an American audience. The lay person is assumed to be too stupid to understand anything. In this case it might be the author also who has not reached the Britney Spears level of understanding of semiconductors. He says “LEDs and SSL [solid state logic?] can be just as complex as you want to make them, especially if you have a thing for semiconductors [like Britney!] or photmetry. It’s one thing to understand the lighting in terms of heat sinks and LEDs, but it’s entirely another to get deeply involved in the electrical engineering, physics, and material sciences… Many of these elements are outside of our scope and are fully explained in white papers, journals, and textbooks, if you’d like to dig more.”]
My personal experiments with LED bulbs so far have been reasonably encouraging. I spent $38 on a Philips L-Prize Award Winning Bulb in October. It is now down to $30. I installed it in an outdoor fixture that requires a ladder to service. The other bulb is a Mitsubishi Verbatim BR30 at the top of a stairwell. This is a truly challenging destination to reach. The bulb produces a beautiful uniform light. It is rated at 85W equivalent but seems brighter. It impossible to tell whether there are really multiple small LEDs inside and the spectrum seems pretty broad. It was a little more than $30 and I got it from a specialist retailer, http://www.lights-go.com, founded by Rick Regan.
The Philips Web site distributes a calculator that shows the payback period for Massachusetts (average electricity cost 14 cents/kwh) is 3.8 years (26.7 percent ROI) when replacing $1 bulbs with $30 LED bulbs that are used 1000 hours per year. As noted above, given that LED bulbs are not substantially more efficient than CFL, it does not seem as though replacing CFL bulbs makes economic sense, though personally my experience with CFL is that the bulbs fail after a year or two, the light is slow to warm up, and disposal of the mercury-laden product is a distressing operation for a parent. A calculation that I have not seen done is of when it makes sense to buy an LED bulb given how quickly the prices are coming down. Even if one is using incandescents it might make the most sense to continue using them for one more year and then switch to a Philips bulb that is selling for $20 rather than $30 today. Philips says that a standard bulb will consume about $7 per year in electricity if operated for 1000 hours. The LED bulb that I bought has already fallen in price by more than $7 in the past month.
Based on my experience as a shopper it is a good thing that both Mitt Romney and Barack Obama constantly reassured me that America is the world’s most innovative economy. Otherwise it would be disturbing to realize that all of the innovative products that I have encountered were designed by people outside the U.S. The leaders in this market seem to be Dutch, Japanese, South Korean, Taiwanese. Does anyone know of a U.S.-based company that will be competitive in this market? General Electric has a 60-watt replacement LED bulb that consumes 30 percent more power than the Philips bulb and costs nearly twice as much.
Finally the advent of these bulbs makes me realize how poorly adapted to the modern world is the wiring in the orgy of new residential and commercial construction that the U.S. indulged in during the last two decades. We spent trillions of dollars building new structures that are wired with the wrong voltage and that have the dumbest possible controls. One would think that every new outlet would have USB power (example) and that every lighting fixture would have a 3.3V or 5V output as well (see this IEEE Spectrum article that explains more of the engineering behind a bulb).
[Separately, I have been shopping for retrofit power strips that contain USB power outlets. Despite the supercharged price and size of some of these devices (up to $50), they often put out a feeble 0.5 amps of power rather than the 2.1 amps required by popular tablets such as the iPad. Monoprice.com has some that are spec’d at 2.1 amps but the typical name brand surge protector is down at 0.5 to 1 amp shared between two USB outlets. Monoprice retails a four-port charger with a total drive capability of 2.1 amps for $7.80. Why can’t a $50 surge protector include the same capability?]