It really depends on what you want to light up.
You can use a longer exposure, and make even a small led light really light things up.
But depending on the situation, you might not be able to use long exposures.
What are you wanting to take photos of?
Will there be ppl in the shot?
I do whats called "painting" light onto the shot.
I do a long exposure, 6 to 15 seconds, and use a light to "paint" light onto the walls, etc.
Here is one of my cave shots,
done with a 3W led, that was waved around the room.
Heres one using the 35W X990 HID to bounce off the ceiling.
Most HIDs are rather spoty, and my create hotspots in your shot.
Such as this one, which is a realitively quick exposure, but you can clearly see the uneven lighting.
If you are wanting to take a normal exposure timed photo,
and just want to light up the surroundings alittle,
not much can beat a good flash, due to its very even light.
But theres only so far a flash can reach.
~John