# High-powered LED bicycle light.

#### Cowsandcowsandcows

Joined Nov 27, 2011
9
First things first, I'm new to this forum, and relatively new to electronics, so I apologise if some of my questions are a bit basic.

Now to the actual project. I'm trying to upgrade a large bike light from using a halogen bulb to using LEDs. It's running off a 4.8v NiMH battery pack with nothing in the circuit except the switch and the bulb. I've found these LEDs, but they apparently require a constant current supply. Maplin also sells constant current supplies, but the lowest voltage any of them operates at is 12v, which is too high for me. I've been reading up on LEDs on the internet, and from what I've read, if I were to use a variable voltage regulator to provide an LED with a voltage equal to its own voltage drop, it seems that it wouldn't need a series resistor to work without burning out. Firstly, am I correct in thinking that?

Secondly, if I am correct, the Maplin website gives the "forward voltage" of the LEDs, is that the same as their voltage drop?

Thirdly, do I really need a constant current supply if I can provide the LEDs with exactly the right voltage, or have I missed something?

#### MrChips

Joined Oct 2, 2009
28,139
The idea is to not waste any battery energy as heat in a drop resistor and to make the battery last as long as possible. If your battery pack is 4.8V, you can wire two 2.4V (2.3V will do) LEDs in series with the battery and you will be ok.

But a flashing circuit with a 50% duty cycle will make your light last twice as long and you will be more visible at night.

#### wayneh

Joined Sep 9, 2010
17,201
The difference between lathe/mills proejcts, and dremel and hacksaw is shocking. That light looks like something that would be sold for \$125, +charger and spare battery!
+1
I'd love to have one of those.