Fog lights and headlights both have different functions, both are used at different conditions. The use of fog lights is to indicate the direction of your vehicle for the vehicles passing from the left or right side of your car. It is often red in color as red is very visual which can more easily indicate the rear or the front of your vehicle. But the headlights are like white lights on the front part of the vehicle, which works to spread the light for a longer distance. Use at night time to indicate the activity and road direction of the vehicle next to your vehicle. Both have different uses, you cannot use fog lights as a headlights.