The Perfect LED Light
Copyright 2001 by Garry Petrie
The perfect LED light is designed for cavers who want an efficient, uniform and constant bright light for caving. This article contains some very specific technical information and it is assumed the reader has a basic understanding of electronics. To build the light, the reader also must have some experience soldering, drilling, wiring and cutting small objects. The list of required tools include a multi-meter, Dremel drill and soldering station. The electronics are available from major semiconductor manufactures has “evaluation” kits, but nothing should prevent the reader from “rolling their own” design. The principle cost of the light is the white LED’s. The best white LED’s are made by Nichia Corporation and are expensive. However, it makes no sense to undertake the project without starting with the best LED’s available.
A variation on the Mega Design is described, which adds six more LED’s and provides for current regulation, as opposed to voltage in the original Mega Design. The yellow LED’s were substituted with green LED’s. This designs accounts for the negative temperature coefficient of a LED, that as the LED heats up, it will draw more current. Either mode of regulation works, provided there is proper thermal regulation in the system.
LumiLeds now has an alternative to the single 5mm Nichia LED’s. It is their Luxeon Star device. It is a single device that operates at 350ma and comes with a built in lens to produce a bright, 10 degrees, beam. This product should make an excellent spot light. Here are micro-photographs of the front and back of the actual die after the phosphorescing dye removed. Be warned, the Luxeon data sheet does not describe a hidden oppositely configured diode with a relatively low Vf. Connecting at power supply equal to the typical forward voltage of 3.5v in reverse will destroy the device.