LED Lighting Question

Hello,

I want to build a bike light for my son. My design has 3 LED lights and battery pack which holds 2 AA batteries. I would like to get the most light out of the LEDs and at least a 4-hour battery life. Can you please tell me what LED bulbs to use for max lumens?

I appreciate any help, I am not sure where else to ask.

Matt

Instead of a simple switch or special purpose LED, what you can do is build a circuit that pulses the LED when power is applied to the circuit. The trick here is that when pulsing, you can apply pulses that are the full peak current that the LED can take, yet keep the average power low. The human eye still sees this as bright because of persistence of vision, so as long as you pulse it at a rate of 30 Hz or higher, we will perceive it as bright. A simple 555 based oscillator can be used for this - it will produce the required pulses when turned ON via the relevant switch on the vehicle. I am not sure if a standard 555 would work with 2 AA cells (3V) - maybe a 3V version might be available... perhaps you could consider a 9V battery instead.

This is wonderful information! Thank you so much.

Do you suggest a online shop where I can purchase this?

I am okay with a 9v battery.

Matt

You Want a dc to dc convertor Buck convertor would do the job quite nicley and super bight diodes The you can power from as low as 3 volts

You can easily build one - google for 555 based square wave generator, there are innumerable circuits.

If anyone wants to help me with this I am willing to pay, please contact me at mg(at)graffx.com

I am looking to produce a few of these and am willing to pay for development and technical drawings for a patent

1) LED: My suggestion is to use high power LEDs that provide super bright light, requires ~3.0 V, draws ~ 250 mA each and are relatively inexpensive (consider Ebay!). Here's an example -- http://goo.gl/jR3wgp (Heat sinks are essential, beware).

2) BATTERY: 2 x AA is not a good idea unless you plan to use a dc-dc converter to regulate 3V, adding substantial cost to design. You can alternatively use a 9 V battery with LM317 acting as a constant current controller (circuit available in datasheet). You can connect the leds to be in series and simply control the current, thereby keeping all the bulbs at same brightness. (Recall, led brightness is a function of current, the voltage drop could be different in each based on material tolerances).

Using a PWM as others suggested will keep the power low, but you will also need a power mosfet to drive high current through the LED load. A 555 will only signal high-low. Now it's for you to decide. Good luck and have fun. Let us know how it goes.