Theme 2: Energy and the Environment Background Material, Nepal Light Project

White Light Emitting Diodes
The light source for this project is a White Light Emitting Diode (WLED) that consists of a small clear glass envelope approximately 8 mm in length and 5 mm in diameter with two power pins attached to the bottom.

Photo of an LED, provided by theledlight.com. For more on how LED's work, view the Technical Information from the LED site.

An LED requires a DC voltage of 3.6 volts and draws a current of 25 milliAmps. Therefore, its total power requirement is less than 0.1 Watt. It operates on the quantum principle which means that it produces virtually no heat and it is very efficient in its electrical to optical power conversion. The WLED is, by virtue of its solid state design, is an extremely rugged and reliable device that is ideally suited as a light source for a flashlight. The useful life span of the WLED is in excess of 100,000 hours of continue use. Another feature of the WLED is that all of the light is focused in one direction.
MORE: Background on LEDs

Incandescent light bulb. Copyright 1991, The National Academy of Sciences. Reproduced with permission from Electric Circuits, National Sciences Research Center.

In comparison, the incandescent light bulb generates light by agitating the molecules of the filament with an electrical current such that a great deal of heat and some light is produced -- the electrical to optical power conversion efficiency is quite low.

The filament continuously loses atoms due to this heating process thus limiting the useful life span of the bulb. The bulb filament and glass envelope are susceptible to breakage if not handled carefully. The light produced by an incandescent bulb is not focused and a reflector must be used to concentrate the light in a particular area.

MORE: Background on incandescent light bulbs

Generating Electricity to power the White Light Emitting Diodes
Currently in Nepal, flashlights are powered by non-rechargeable, alkaline batteries. The battery life in flashlights is relatively short and the disposal of "dead" batteries is creating an environmental concern in this part of the world.

One of the key components of the Nepal Light Project is Pico Power. The philosophical guiding principle of the Nepal Light Project is that LED's require extremely small amounts of power (Pico power) to produce enough light to read a book or to get home safely at night.

The systems currently being designed are very simple and low tech and consist of:

• a pico powered wind turbine or
• a pedal generator made from second hand permanent magnet motors
• scrap metal
• a relatively small, sealed lead acid rechargeable battery
• voltage regulator

The pedal generator can be used to recharge a 5 AH sealed lead acid battery from a fully discharged condition with only a few hours of gentle peddling (hands are free for other activities). The fully charged battery can store enough energy to power a set of 6 LED's for a week.

The researchers involved in the Nepal Light Project are working with the Nepalese people to supply an affordable, rechargeable system for the batteries used in flashlights.