I’ve added a new section to the sidebar for LED lighting. While LED lighting is presently very expensive, there are some applications in which it is preferable to compact fluorescent and ultimately LED lighting promises to be much more efficient, provide better color rendering, have a much longer life span, and be less expensive than compact fluorescent without any toxic mercury (but there are other toxic substances such as arsenic, although generally in significantly lower quantities).
We use a tremendous amount of energy for lighting. Compact fluorescent greatly improved lighting relative to incandescent lamps and even somewhat over the larger fluorescent tube lamps. Incandescent lighting tends to turn between 3-5% of the electricity it uses into visible light while compact fluorescent tends to turn between 15% and 20% of the energy consumed into visible light.
LED stands for light emitting diode. It is a solid state device that acts like a solar cell in reverse. LEDs in their pure form produce a very narrow band of light frequencies so they have a distinct color such as red, orange, yellow, green, blue, etc. White LEDs are being manufactured for illumination purposes but these actually are usually blue LEDs with a broadband yellow phosphor that converts a portion of that yellow light into a broadband yellow spectrum light. Single color LEDs can be made with efficiencies that very closely approach 100%, but white LEDs currently in production are usually on par with compact fluorescent efficiencies with 15-20% efficiencies though some of the very best approach 30%.
This method of making white light actually is spectrally very sparse and renders colors very poorly. A better and potentially much more efficient method is to combine a red, green, and blue led into one unit. This can produce a LED which has spectral output in all the same energy bands that our eyes have receptors and thus can render colors much better. Until recently, ultra-bright and efficient red and blue LEDs existed but ultra-bright green LEDs were not as efficient and limited the overall efficiency of a LED light using this technology. However, recent advances now make it possible to make an ultra-bright and efficient green LED but this type of RGB LED isn’t yet in wide production.
So while present LED lighting tends to be insanely expensive, only about as efficient as compact fluorescent, and with a similarly icky color rendering index, the potential exists and has been realized in the lab, for LED based lighting that is nearly 100% efficient or about five times more efficient than compact fluorescent, and that has an excellent color rendering index. This is about as large of an improvement in efficiency over compact fluorescent as compact fluorescent is over incandescent lighting. Hopefully we will see these get from the lab into full scale production and costs drop out of the stratosphere soon.
LED light lifetime also tends to be much better than compact fluorescents, with typical ratings from 30,000 to 70,000 hours, however, this is actually much better than the numbers indicate because of the difference in the way lifetimes are rated. Compact fluorescent lamps are considered “dead” even in the absence of complete failure when their output drops to 50% of their new output. LED lighting is considered “dead” when it’s output drops to 70% of it’s new output. If LED lifetimes were rated at 50% instead of 70% output, they’d be much longer. Also, compact fluorescents frequently do fail outright rather than just dimming, but in the absence of some external abuse, LED lamps rarely do, they just get progressively dimmer with age. Lastly, the rate that LED lamps dim is dramatically lower when operated at less than 100% rated output power and their efficiencies are generally higher at below 100% rated output power.
One additional difference, compact fluorescent lamps perform poorly in cold temperatures owing to incomplete vaporization of mercury used in the arc tube but LED lights are generally more efficient at lower temperatures. LED lifetimes are longer at lower operating temperatures.