I am building an electronic metronome for my mum. She has stipulated that she wants a short beep every clock pulse and a light flashing every 3 or 4 clock pulses. so I have built one for her. Unfortunately the array of four superbright white 5mm leds I am currently using is not bright enough! I have decided to employ the services of a logic level, n-channel, power mosfet to drive it. I am running the metronome from 3 AA batteries. What I am wondering is will i need a current limiting resistor if the on time is less than 40ms at a mark:space ratio of 100:1? or will the internal resistance of the power pack limit the current sufficiently?