Now real light bulbs have filaments and light is emitted all along the length of the filament. Some are just straight lines (actually curly but form a straight line) and some form U shapes. This is a straight filament using 4 radials very close to each other. Not much different than the single point except for a very slight softening of the shadow edge. I was expecting a bigger difference but looking at a similar light bulb(clear) in my house this is true. So for these types of lights a single radial will probably work just fine. Render time 1:56