Light-Emitting Diodes (LEDs)
What is the most energy efficient way of illuminating work and living spaces? Are compact fluorescent lights and LEDs as good as incandescent lights?
10% of energy used by humanity is used for lighting. How much can we save? Is there any difference in light quality between incandescent and fluorescent lights and LEDs.
Compact fluorescent lights are replacing incandescent bulbs everywhere. They save us about 75% of energy at similar illumination levels and last much longer. They still cost more but the initial higher cost pays back quickly in savings. Are they the ultimate technology?
In places where energy is much more important than cost like in recreational vesicles of sailboats we very often replace both incandescent and fluorescent lights with LEDs. What are they?
Light Emitting Diodes work "opposite" to solar panels. Current passing through the junction of the diode consists of electrons and so called "holes" (empty spaces, where the electrons are missing, which can be treated as mobile positive charges). When "holes" and electrons meet in the junction of the diode they recombine (electron at the higher energy level fails into the hole, which is at lower energy lever) producing visible photons. This is a very efficient process but creates monochromatic light. There are two ways to make white LEDs. You can either make red, green and blue diodes in one package, this combination will look white or you can have violet or UV (ultraviolet) LED covered with appropriate phosphorous material, which absorbs violet or UV and emits white.
For a long time we were only able to manufacture small LEDs used as indicator lights and little displays. The technology however improved dramatically in the last 10 years and LED replacements corresponding to incandescent lights of 60 or 100 W are available.
LEDs have the efficiency (the amount of light in lumens or number of photons produced per unit energy) similar to fluorescent lights but contrary to fluorescent lights they emit light approximately into a half sphere rather than full sphere. So if we want to illuminate a particular surface (for example a book or a work table they are more efficient. They are also much smaller and last longer.
As you can see on our video to illuminate a surface with about 500lux (which is a good reading illumination) from the same distance we need 57 W for incandescent light 11 W for compact fluorescent light and 9 W for LED.
Lighting and Energy.mov (right-click and choose "Save Link As..." to download to your computer)
© Physics and Astronomy Outreach Program at the University of British Columbia (Brittany Tymos and Andrzej Kotlicki 2011-03-10)