The amazing progress of LEDs

81 points by lesterbuck 11 years ago | 51 comments

beloch 11 years ago |

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 11 years ago | |

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 11 years ago | | |

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...

grimman 11 years ago | |

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 11 years ago | | |

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.

Scaevolus 11 years ago |

Related: "Drowning in Light" from a few weeks ago: http://nautil.us/issue/11/light/drowning-in-light https://news.ycombinator.com/item?id=8344769

It makes the compelling argument that people are addicted to light. "Tsao calculates that, as a result, light represents a constant fraction of per capita gross domestic product (GDP) over time; the world has been spending 0.72 percent of its GDP for light for 300 years now. If there are other energy markets that show a constant percentage of GDP expenditure over time, Tsao doesn’t know of them."

jcampbell1 11 years ago |

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 that works on it is my hero. My family bought power for $.04 KW/hr, so I could study at night.

witty_username 11 years ago | |

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

seanalltogether 11 years ago |

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.

ghostly_s 11 years ago | |

The Emerge Alliance[1] is an industry group that has been working on this issue, though they've started with a spec for datacenters (as stephen_g alludes to). I think the consensus is that it is definitely more efficient to convert to DC at a single point, but one located as physically close to the loads as is practical, because of the line losses mentioned. Definitely something that will make sense for commercial buildings/campuses and multi-unit residential, and single family homes are not too far behind, I think. I can picture homes sometime soon just being wired for AC in the kitchen/garage/utility rooms with a LV DC grid elsewhere. The lower safety requirements for low-voltage really open up possibilities for system design and integration in the built environment.

http://www.emergealliance.org/About/Vision.aspx

stephen_g 11 years ago | |

Line losses through the cables are usually a killer with really low voltage DC (like 5V or 12V), so I think that AC would be more efficient there.

But some datacentres are using 48V DC now and then just piping that through a switching regulators in the servers instead of going from AC to DC. That could be workable.

teh_klev 11 years ago | | |

48V DC has been in multi-client data centres (Telehouse, TeleCity etc) for years. It's a standard voltage in telecoms kit. The data centre I was involved in building out back in 1999 got this as standard.

webignition 11 years ago | |

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.

ZoFreX 11 years ago | | |

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?

RoboTeddy 11 years ago |

One problem with current popular LED bulbs:

They emit more blue light than incandescent bulbs [1]. If people light their households with LED lights at night, it might shift their circadian rhythms [2]. Screwed up circadian rhythms can have all sorts of negative health/productivity effects.

[1] http://www.designingwithleds.com/measuring-light-quality-phi... [2] https://justgetflux.com/research.html

montecarl 11 years ago |

Exponential growth is awesome! However, I was curious about the maximum theoretical lumens per watt to determine when the growth will fall flat. A current LED bulb gives about 60 lumens per watt. While an ideal monochromatic light source could give 683.[1] So it looks like there is _only_ one order of magnitude left in efficiency gains.

1: http://en.wikipedia.org/wiki/Luminous_efficacy

jzwinck 11 years ago | |

That 683 lumens per watt number is, as you say, for a monochromatic light. This is not useful for humans to see with[1]; the actual limit for human vision is about 300 lumens per watt[2]. That's an upper bound even ignoring losses, and some LEDs are around 70 now, so the remaining efficiency gains we can make seem limited to about 3x.

[1] http://www.cool.conservation-us.org/byorg/us-doe/color_quali...

[2] http://phys.org/news202453100.html

Yardlink 11 years ago |

He makes some dubious efficiency claims. It's true the colored LEDs have always been pretty efficient, but that's no use lighting your home. White LEDs have surpassed incandescent bulbs but still have a way to go to reach flourescent tubes and the grand-daddy of efficiency - gas discharge lamps.

One (the?) reason for low power levels is they generate so much heat and are difficult to cool. LEDs are still primarily heaters - useful in the winter.

ghostly_s 11 years ago | |

I think you need to update your figures. High-end consumer luminaires have been coming in above 100 lm/watt total system efficiency for at least a year or so now, and with CRI superior to fluorescents.

Yardlink 11 years ago | | |

Great news. I guess efficiency is following a similar rapid growth to power.

robomartin 11 years ago |

Several years ago I designed 1,500 W LED-based light source using extremely tightly packed LED's. Thermal management was a huge challenge. It took over three months of constantly running FEA thermal tests as well as physical tests to zero-in on an innovative approach to cooling the array. Crazy project. The surface of the emitter was measured at over 60,000 candelas per square meter. You simply could not look at the thing directly, it was really dangerous, almost like working with lasers.

johnm1019 11 years ago |

I'm a bit disappointed they didn't include a legend on the giant chart they put in the middle of the page.

jsilence 11 years ago |

Why do I have to enable "whatsappsharing.com" in my NoScript filter to see the graph?

jonathansizz 11 years ago | |

Because you're using a browser extension that breaks the web.