May as well just do glow effects in Photoshop unless your animating, but if you want to bump up the illumination power of ambient surfaces, them increase the scale value in the final gather settings in the render globals. It's a colour value but if you use HSV mode you can increase the value to greater than 1 to give the scene more power, like an exposure control.

Can't remember if I've already said that or not.

gio