X-Light LED

Copyright © 1996 Jørn Yngve Dahl-Stamnes

Last modified: Wednesday the 01. of September, 1999

What is it made of?

The X-Light LED is a home made tail light based on four high-intensive GaAs red LED (Light Emission Diode). Each LED (produced by SHARP, Type no. LT9512U) produce 4000-6000 mCd (Cd = Candela) and have a 14 deg. light angel (+- 7 deg. measured with the center line). The LEDs are packed inside a waterproof plexiglass unit.

Ohm's law

Since the unit gets the power from a 12 Volt battery, a resistor is required to controll how much current the LEDs are using. Each LED have aproximatly 2 Volt between the pins @ 20 mA. With 4 LEDs connected in serie, this equal to 8 Volt. The resistor ensure that the current floting through the LEDs are 20 mA. By using Ohm's law:

R = U/I
R = (12-8)/0.02
R = 200 ohm.

I use a 220 ohm resistor, since it is the closes value I can find in the R14 series. Of cause, 180 ohm could also be used without any problem. With 180 ohm, the current flow would have been greater (22.2 mA) and the light a bit stronger.

The power consumption in the resistor is equal to I*I/R, which in my case give 0.088 Watt (88mW). That is not much, so as long as you are using a 12 Volt battery you don't have to worry about overloading the resistor.

Construction

The four LEDs and the resistor are placed inside a unit made of two plexiglass pieces. First, in the solid plexiglass piece, I made a well where the pins from the LEDs and the resistor could be connected together. The well is split in two parts with a smaller well (more like a channel) between them where a wire can go. The reason to have two well is to make place for three screews to fasten the back cover (see below).

Then I drilled out a large hole for each LED, two LEDs in each well. Each LED was placed in a hole and connected together. The resistor is placed together with the LED in one of the wells.

To be able to connect the LEDs to an external power source, I put two screws on the back cover. By making the holes for the screws smaller than the scews, the unit will remain water proof.

The back cover is held by three screws to the solid plexiglass unit. A gasget between the two units keep any water away from the LEDs and the resistor.

The X-Light LED is attached to a aluminum plate with an red cat-eye mounted to the carrying rack. One wire is connected to the rack (ground) while the other is going to the main switch for the X-Light II. As long as one of the head lights are one, the X-light LED will be on.

More information will follow later (photos and drawings).

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I made this! Jørn Dahl-Stamnes