Does anyone know the difference between the two kinds of bulbs? Are the h3s just smaller? Because you can get both h3 and h4 in 55w. Do they put out the same amount/kind of light?

 

besides the fact that they're totally different bulbs for different applications? you can get household light bults in 35 watt also. h3's are generally for fog lights, h4's are generally combination hi/lo beams.

h3:


h4: