I changed my headlights about a month ago. Now my left headlight is much brighter than the right one. Is it a problem with the bulbs? What is it?

 

Exchange the bulbs. That will reveal if the problem is with the bulb or the circuitry. When you do this, look at the bulb bases and sockets for signs of overheating.

 

properly and could be deciving to the untrained eye,but yeah try to swap sides with the bulbs first.

 

Maybe you melted a harness if they're over wattage

 

left = passenger side?
or left = driver side?

it depends on your perspective

the pass side is almost always brighter on the US spec vehicles as to not blind oncoming drivers.

 

My drivers side is brighter...

 

I bet it is the aiming. The driver's side headlight is supposed to be aimed towards the center of the road to light it up and to not blind oncoming drivers. The passenger's side headlight is supposed to be aimed toward the right side of the road, to illuminate the curb or shoulder. So if you are directly in front of the car, you'll see more light from the driver's side, since it's aimed directly at you and the passenger's side is aimed to your left.

 

if you changed both...they should look about the same brightness....
now if you only change one bulb..then you might get that different brightness.
again...it might be true that the passenger side kinda brighter as not to blind the oncoming traffic...but I think my car has the same brightness on both side..oh well...
=]