Integrated Reflector Could Lead to Ubiquitous LEDs

Andreas writes "Professor Schubert says he has found a way to raise the efficiency of LEDs to 99%. From an article on Advanced Technology: "Until now, all lighting systems, especially incandescent bulbs, generated more heat than light. But our 99-percent efficient reflectors for LEDs makes them the first candidate for light-bulb replacement that generates more light than heat," said Schubert."

Comments

110/230V AC

[EnglishTim]

Okay, so let's assume all our lightbulbs start being made from LEDs... At some point soon we're going to have to start changing our lighting circuits to 5V, or something like that. It's madness that each lightbulb will have to contain it's own little transformer - it'll make the bulbs vastly more expensive and wasteful.

There are a selection of appliances that work well with 110/230V AC - things that require a lot of power like kettles, hoovers, heaters, washing machines, hobs, tumble driers and the like. However, there's an increasing number of appliances in a modern household that would be much better served by a 12V DC supply.

How long do you think it'll be before we start changing over?

Re:110/230V AC

[Peepsalot]

It's madness that each lightbulb will have to contain it's own little transformer - it'll make the bulbs vastly more expensive and wasteful.

Sorry, I don't think you'll see a change(at least not to a lower voltage) in your wall outlet's voltage any time soon. Maybe a transformer in every light bulb seems wasteful, but take into consideration that led's can last roughly 100,000 hrs as opposed to 1,000 for incandescant's.

Still seems wasteful?
Transformers don't have to be huge, especially if they are powering an efficient device that doesn't draw much power. Disposable cameras contain transformers in them that step the voltage from 1.5 to 300 volts, and they are pretty damn small. In fact you could fit a transformer into just the metal base of a normal incandescant bulb. Not to mention the transformer's solid state cousins: voltage regulators, swithcing power supplies, and probably some others I don't know about (IANAElectrician.)

In fact, you could also scrap the idea of stepping down the voltage entirely. How about putting more led's in series. Think about it, led's emit a narrow spectrum of light, so to smoothen out the spectrum, you might want to add a bunch of led's from different parts of the spectrum. Just put 40 little 3v led's on a board and voila, you have a device that accepts 120 volts. Another reason to use a large number of leds: you might want to spread out the surface area where the light is coming from, a single point of light could seriously mess with your vision. Not to mention the fact that I doubt to see any single led in the near future that can output the equivalent of a 60 watt incandescant light bulb.

But the thing the I wonder about is if and when the standard plug model will be changed to a model where the socket and the plug contain coils to transfer the power, like an isolation tranformer that is split into two parts.(Have you ever seen how a sonicare toothbrush charges itself?) The main benefit I see in this is safety; never have any exposed wires to fry yourself with. Actually, if all your wall sockets had coils in them, the plug of your device could determine the voltage that device receives, simply by the nuymber of coils in it. Again, IANAE, so I don't know, maybe it would take the advent of room-temperature superconductors to make this idea feasible and efficient.

Re:110/230V AC

[rco3]

A few points to note, realizing that not many posters around here are EE's:

1) LED's are not voltage mode devices. There IS a typical voltage drop associated with an LED, but it can vary appreciably between devices. One sets the operational point of an LED by controlling the current through it, and allowing the voltage to settle to whatever value it wants. Typically, one would want to see around 30 mA through a normal T1-3/4 LED. Depending on the chemistry of the LED, this could result in a voltage anywhere between 1.5V and 3 or 4V. This, as I said, will vary somewhat between different LED's of the identical type. If you try to set the voltage, you'll get wildly varying currents and a lot of dead LEDs.

2) Stringing together LEDs in series to get something approaching 120V drop is a good idea, but you still have to limit the current. Leaving a few volts between the nominal operational voltage of your LED string and the nominal supply voltage is a good idea, because you can then use an active (or passive) current limitation scheme which operates within that voltage gap. The simplest way is with a single resistor, sized such that R= (Vsupply-VLEDS)/ILEDS. This is subject to variation due to device mismatch, temp variation, etc, and dissipates some power in the resistor. Another way to do this, which allows for the LED to be operated from a much higher voltage than it's rated for, is to use a series capacitor. The determination of proper capacitor size is a bit more tricky, but you can successfully run a single LED from a 120V supply. The indicator in my waterbed heater has run this way for a couple of years now. Nice part is that the capacitor does NOT dissipate any power as heat. Enough of them might screw up your power factor enough to piss off the power company, though :-)

Important messages to take home from this: you can't set LED operating point from the voltage across it, at least not safely and reliably; you can operate LEDs from 120VAC using a capacitor as the gain setting element, which is appreciably cheaper than using a transformer.