Then?

How do we use it in bikes?

I will answer with my limted electronics knowledge. 7805 is rated for 5V. A 1W HPLED needs 3.4-3.8V. So i would use a 7810 (rated for 10V) and connect it to 3x 1W HPLEDs. The HPLEDs being in series. This would gve each 3.333V. P=V.A, 3W= 10V. xA, x=3.33A But according to the HPLED specs. sheet each draw 350mA. So that would be 1050mA for 3, around 1A. Since we are giving less than the rated voltage, current should be lower than 1.050A. But still not low enough for use without a HS.

Oops i failed . Will have to think of a better combination.

Each normal LED is 20mA or so! That is like some 50 LEDs in parallel.

For high power LEDs, special driver ICs are there for accuracy.