Solid-state light bulbs

[q2261]

I was just reading an article about LED light bulbs. Does anyone have any insight about these? How much is it going to cost? How much of an improvement is it really going to be over fluorescent and/or standard tungsten bulbs? Also, could someone talk about the technology involved?

 

[Howard]

LED light bulbs? LEDs have already taken the place of standard electric resistance light bulbs in many applications.

 

[dkozloski]

I carry two LED flashlights in my pocket every day. The batteries last in excess of 100 hours. Practically every new traffic signal has clustered LED light sources. Thay can be spotted by the very smooth even light and great directivity.

 

[Mark R]

LEDs are good where low levels of light are required.
I've got some 'super-flux' LEDs (far more light than conventional LEDs, although not as 'bright' due to a wider beam) which are widely used as automotive tail lights - they are also excellent for decorative lighting. However, for illumination, they really aren't bright enough.

There are some new very high light output LEDs, sold under the brand name 'luxeon' - the most powerful white model is about as bright as a 15 W light bulb, but has the advantage of using only 5W power, and lasting at least 25,000 hours (and potentially as long as 100,000). Disadvantages are the need for heatsinking and the high cost ($40 each in small quantities!!)
Luxeon LEDs are bright enough to be useful, but at $10 each for the low-power (1W) ones, they are not mainstream. However they have found uses in portable devices such as flashlights, and bicycle or caving lamps. Coloured Luxeon LEDs have also found their way into auditorium and stage lighting where RGB mixing provides new found lighting flexibility.
Power efficiency for white LEDs is about the same as a good halogen bulb, slightly better than a conventional incandescent, but considerably worse than a fluorescent. Coloured LEDs are more efficient.

 

[Eskimo]

Not sure if this is the article you were reading but it's a pretty good read on the subject of GaN LED technology.
IEEE Spectrum Article

The color of the light emitted from an LED is a function of the bandgap difference between the doped regions of semiconductor. The only manufacturable material that I know of that produces white light at reasonable intensities for lighting is GaN as discussed in the article above. Unfortunately the technical limitations of current substrate production are such that GaN wafers above 4" in diameter are near impossible to produce. In contrast Silicon wafers of 8" are common in production with much of the industry moving to 12". This small size limits the number of devices you can form per wafer. Additionally as I understand the cost for a single wafer of this size is approximately $50,000, compared to less than $100 for a 8" silicon wafer.

I believe that give a few years like most integrated circuits the price for white LEDs will come down in price. Given the fact that they last almost infinitely longer than a standard light bulb and produce very little heat I'm sure a market will emerge for them.

 

[dejitaru]

If something gets hot enough, it glows. Incandescent technology exploits this coincidence, yet wastes 95% of the energy put into it. LED's convert electricity directly into light.
There is litle reason not to replace your incandescents with LED or flourescent.

 

[Knavish]

There are companies working on LED lightbulbs, but I've never seen on for sale or even a demo product. The biggest challenge is that you can't get a single LED to emit white light. LEDs are good at producing near-monochromatic light (i.e. blue, red, yellow, etc) but they don't produce light over a large spectrum. They are also good at producing very intense light, especially in certain colors like red. The only way I know of getting white light out of an LED is either combining a cluster of red, green, & blue leds in a small package or to put a phosphorescent coating on a blue/UV LED that will glow a whitish color in response to the bluish LED color underneath. (some can be quite white, but many are very blue/white). LEDs, however, do have a much better lifespan and effeciency than either incandescent or flourescent bulbs. The biggest problem is that white led arrays are EXPENSIVE.

Here's a place selling led lightbulbs (crazy expensive):
Linked
[30 Watt Equivalent bulb = $190, 150 Watt Equiv. Flood bulb = $700!!!]

For the 150W flood bulb, I did worked on the math a bit & it looks like I'd break even after about 48,000 hours (5.5 years) of continuous use! Assuming both bulbs would last that long...

 

[jasonja]

My friend works for a company that is replacing the little light bulbs in planes (the ones passangers use to read) with LED bulbs. These would last a very long time.. maintance costs are more than the price difference the bulbs. Sometimes the price of replacing the bulb is enough to justify the extra cost.

Traffic lights are another great spot... one LED goes out no big deal.. the whole light goes out and chaos breaks out.