I've seen outdoor fixtures with 2 bulbs, installed with the wiring set such that 1 bulb was wired to the photocell and was on all night, but the other bulb was wired to the motion detector, so it came on only when there was motion. Thus there was 75 watts of light all night, but that jumped to 150 watts whenever motion was detected. (Assuming standard 75W floodlamps. Trying different sized bulbs will allow you to adjust the light however you want.) Or you can use 2 separate fixtures, one on all night and one entirely motion detection triggered.

That's a simple and cheap way to do what you want.