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The amazing progress of LEDs

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Re: The amazing progress of LEDs

#21

Post by witty_username »

jcampbell1 wrote: post #2

Certain things are cheap in the rich world that are expensive in the 3rd world. Sewage, electricity, and water are so cheap in the 1st world, that we don't think about the cost. The first time I saw 100% adoption of compact fluorescents was in Cambodia. They pay $.40/KWhr. That is insanely expensive (unless you live in Germany). Lighting technology disproportionally benefits the poor rather than than the rich. Anyone…

While Bangalore is not representative of India as a whole, the electricity prices are similar to global figures.

Re: The amazing progress of LEDs

#23

Post by mnw21cam »

grimman wrote: post #20
beloch wrote: post #12

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 hundre…

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?

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.

Re: The amazing progress of LEDs

#24

Post by webignition »

crististm wrote: post #18
webignition wrote: post #15

Earlier quoted context omitted.

Interestingly, I'm looking to do exactly this in a new home (new to me, not newly constructed). I'll soon be moving to a park home (a relatively-permanent mobile home) that is in need of a fair amount of renovation. I'll be running all lighting, computers and the TV off 12v DV circuits powered by bank of vehicle batteries and where the batteries are charged from 12v solar panels.

Have you considered cabling loses? There is a reason power lines use very high voltages.

I've considered voltage drop over cable length only in as far as I'm aware that it occurs. I haven't tested the level of voltage drop.

I currently use 12v circuits in my camper van and haven't experienced any significant drop over cables about 3m in length. LED-based lighting and a 12v fridge operate as expected and the voltage at the point the power reaches these devices is very close to the voltage over the battery supplying the current.

I previously used 12v circuits in a narrowboat I used to own and didn't experience any drop over cables about 20m in length. This used halogen-based lighting and again the voltage at a lamp was very close to the voltage over the battery.

Re: The amazing progress of LEDs

#25

Post by patrickk »

beloch wrote: post #12

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 hundre…

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...

Re: The amazing progress of LEDs

#26

Post by ZoFreX »

patrickk wrote: post #25
beloch wrote: post #12

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 hundre…

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 furt…

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...

Re: The amazing progress of LEDs

#27

Post by ZoFreX »

webignition wrote: post #15
seanalltogether wrote: post #5

I'm genuinely curious whether new homes will start wiring lighting for DC to accommodate all these new LED bulbs? I just don't have a good sense whether its more efficient to transform AC to DC at a central hub in the home to distribute to all rooms, or more efficient to do it at the bulb itself.

Interestingly, I'm looking to do exactly this in a new home (new to me, not newly constructed). I'll soon be moving to a park home (a relatively-permanent mobile home) that is in need of a fair amount of renovation. I'll be running all lighting, computers and the TV off 12v DV circuits powered by bank of vehicle batteries and where the batteries are charged from 12v solar panels.

Converting voltages is trivial with AC, how do you handle devices that require something other than 12v (lots of phones want 5, lots of laptops want 18) with a DC system?

Re: The amazing progress of LEDs

#28

Post by grimman »

mnw21cam wrote: post #23
grimman wrote: post #20

Earlier quoted context omitted.

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?

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 | .-' || '-.…

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. :)

Re: The amazing progress of LEDs

#29

Post by patrickk »

ZoFreX wrote: post #26
patrickk wrote: post #25

Earlier quoted context omitted.

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 furt…

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...

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.

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