True "fog" lights only cast light to the sides and very little to the front. The idea is to illuminate the sides of the road to give more visibility to the edge of the road so you don't off the road. Ifyou put them behind a grill they will illuminate the inside of your radiator area.
You may actually want driving lights which will illuminate the road ahead. The actual pattern is quite narrow (as to not blind oncoming drivers) and usually goes further than your low beams.
Companies often interchange the terms, so be sure you know what you are actually buying.
Once installed, don't forget to take the time to aim them. I usually cover the headlights when I aim them. It makes the pattern more definable.