Brightness or burn time, a question of balance
Brightness and burn time are two inextricably linked parameters of any headlamp, regardless of its lighting technology. For a given quantity of energy, increasing the brightness automatically decreases burn time, and vice versa.
For a compact headlamp worn entirely on the head, the energy source (standard or rechargeable battery) often has a limited capacity in order to reduce size and weight for the sake of comfort. In spite of the improved performance of today's LEDs and batteries, this still limits the capacity of a headlamp to provide both significant brightness and long burn time.