[beloch]

One interesting application for super-bright LED's is home theatre projectors. Until very recently such projectors used lamp modules (usually metal-halide) that typically have an operating lifespan of a few thousand hours at most. That's a very rough estimate. Failures can happen sooner and they occasionally implode. Also, brightness usually drops off gradually as lamps age. New lamp modules usually cost a few hundred dollars. These lamps also produce a large ammount of heat and require active cooling, which makes projectors noisy unless carefully designed for quiet operation. For these reasons, home theatre projectors probably remain more of a niche product than they might otherwise be.

LED based lamps are starting to show up in this market sector. Current LED-based projectors are mostly portable projectors that offer low brightness and poor image quality, but some home theatre models of decent quality are starting to appear. At present, they're expensive, less bright than most projectors based on traditional lamps, and still require fans for active cooling. However, as LED's become more power efficient and economical, these projectors will hopefully become brighter, passively cooled, and significantly cheaper.

Projectors are not appropriate in many environments, especially those with high ambient light levels, but LED's may help them make major inroads into the big-screen market.

[patrickk]

Another interesting application: growing vegetables very efficiently (potentially in urban areas).

"Plants mainly need blue and red light for photosynthesis and far-red, a colour not even visible to the human eye but visible to the plant….."

This makes LEDs very interesting for this purpose - the ideal light spectrum can be achieved with LEDs. This will make more and more sense over time as the world urbanises further and LEDs get ever cheaper.

http://www.bigpictureagriculture.com/2011/02/plantlab-nether...

[ZoFreX]

I can think of a large market for lighting suitable for growing vegetables in your home that doesn't produce a lot of waste heat...

[patrickk]

It's already been done (LEDs for growing weed, impossible for cops to spot growhouses using FLIR helicopters and much lower power usage so spikes in energy consumption are far less dramatic).

I think in terms of impact, growing vegetables in a sustainable manner that uses little water will be critical for the long term sustainability of cities where water is scarce, such as Dubai or other cities in desert regions.

[anonbanker]

Some people in that market are already seeing harvests equal to 1gram per watt on LEDs. And the quality is as good as a much hotter high-pressure sodium bulb of higher wattage.

[grimman]

For more stationary projectors, couldn't you just make a larger LED array and focus the light through a lens, rather than try to do cram super bright, and presumably expensive LEDs into a regular bulb sized package?

[mnw21cam]

Short answer: No.

Long answer: Typical projectors have two lenses. The one at the front is obvious, since it focusses the image of the LCD/film onto the wall. Just behind the LCD/film is a collimating lens (usually a Fresnel lens), which ensures that all the light produced by the lamp is focussed so that it passes through the first lens. Something like this:

           |Collimating lens
           ||LCD
  Lamp   .-||-.      |Main lens
  |   .-'  ||  '-.   |   .-'
  |.-'     ||     '-.|.-'
  O--------||--------|------
   '-.     ||     .-'|'-.
      '-.  ||  .-'       '-.
         '-||-'

The light brightness over the plane of the LCD/film must be very even, and this is achieved by having a lamp situated a fair distance behind it. The lamp itself must therefore be small in order for its focussed rays to fit through the aperture of the main lens. In fact, the lamp must be (usually) no larger than the aperture in the main lens.

It is conceivable that you could arrange an array of LEDs behind the LCD, but you would have to arrange that all their rays are focussed through the main lens. The prevents us from using a large array of LEDs in the same arrangement as above, as the light from the LEDs at the edge of the array would not pass through the main lens. An alternative would be to place the LEDs closer to the LCD, and give each LED a lens sufficient to focus its rays through the main lens. Something like this:

       O.|LCD
  LEDs   |-.      |Main lens
  with   |  '-.   |   .-'
  lenses |     '-.|.-'
       O-|--------|------
         |     .-'|'-.
         |  .-'       '-.
         |-'
       O'|

In this case, each section of the LCD would be lit by a different LED, so you would have to be very careful to keep the lighting brightness and colour even. LEDs vary in colour and brightness naturally.

[grimman]

Ah, well that's a shame then. In retrospect, if I have thought of it, the people whose actual job it is will almost certainly also have thought of it. But thanks for the excellent info and lovely ascii graphics. :)