Also not an auto electrician but a few thoughts:
I assume you mean that the headlights are not as bright as you would expect and do not provide enough light on the road.
Initial things I would look at would be are the lenses of the headlights obscured by dirt or condensation, if water has got into the area then they might mist over. Or possibly yellowed with sunlight.
Are the headlights accurately adjusted, they may just be pointing down too low and need adjusting upward.
If the lights are just dim then I would expect a high resistance joint on the cabling, i.e. a loose or corroded connection that is limiting the current, however if it is both lights than it would be before the fuses as they tend to be fused separately.
