3Watts Power LED with 45deg Lens

Now a days white power LEDs are becoming popular, cheaper and more efficient. This makes it easier to use white LEDs as torch lights. You might have seen cheap Chinese torch lights available in the market.
Now why should we add a torch light to robot ?
Most of us have made roborts which can move, navigation enabled etc. Adding a torch light will help us to use it during night also. It is also cheap, I found the LED and lens shown in the picture for just INR105(around $2.5).

Lens and LED kept seperately

1.  Selecting the power LED. There are power LEDs available with various power ratings. Common ones are 1W, 3W and 5W. Here main thing to consider will be more the power rating, more brighter the LED will but less will be the battery life. Choose one with a metal base, because power LEDs draws lot of current compaired to ordinary LEDs which makes it very hot. Metal base helps the LED to dissipate the heat fast.
2. Choose the lens depend on the requirement. In the local market, I have seen Lens varying from 40deg to 75deg. Here lower the angle of lens narrower will be the beam of light.
3. Driver circuit: This is the most important part. Driver circuit has to designed considering the power consumption(more power consumption = less battery life), whether you want control the brightness using PWM, life of the LED, price of the components used in the driver circuit etc. Driver ICs are also available(ZD850 is one which I found on internet)

We can find a lot of circuits if we serarch on google. I have listed below some of the circuits which I found useful.

1. Microchip has article Buck Configuration High-Power LED Driver, which is based on based on a buck topology switching power supply using the on-chip comparator peripheral within the PIC12F675 microcontroller.
2.  A very simple circuit using regulator IC LM317.
3. Another circuit by dan.

You can search on Google for more information.