Before you drill holes, try following method. it worked with me. I got a pair of headlights from Valeo. On the day i replaced them with the old ones, it was rainy and humid. I left the lights cover open for quite some time, since i have to put all the bulbs in and change the motor. When headlights were on, with all the lights switched on, and rain was pouring on the lenses, they immediately start to condensate.
I tried many methods how to get rid of condensation.
- First i dry them with all the lights on (long, main, position) and with open covers - after some time, closed the covers - no go
- than i add the hairdryer. I hairdryed them for about 5 minutes each - no go
- I put the headlights in an oven on 50C with the thermo/humid meter in, and let the humidity drop to 20%. Get the headlights out and leave them in the room until they cool down. Closed the covers and put them on the car. All was fine, until the first time, lights were on for a longer time. When i switched them off, after 5', condensation start. So - no go
-repeat all the mentioned methods, and always seal the covers (i used hand creme) - no go
- put silicagel and rice in a sock, and put it inside the headlight. - no go
The results were always the same. When the lights were on long enough to get warm, immediately after switching them off the condensation start.
Than i spent some time thinking about this problem.
The point is, that the air inside the headlight chamber gets very warm. When lights are switched off, and if its cold outside, condensation will start on the lense (from inside), specially if the air inside the headlight has high humidity. Bigger the humidity, bigger the condensation.
So this leads us to following conclusions;
- if trying to hairdry or dry with lights on (or both methods) we will always get to same situation, this is warm on the inside/ cold on the outside and as a result condensation
- ideally we would need SAME temperature on the inside and on the outside, just that the air inside the headlight chamber has as low humidity as possible. Vacuum would also be fine, but how to achieve this?!?
With this in mind, i waited for a cold and dry day. Strong dry NE wind was blowing for a couple of days and the air humidity dropped on 31%. The outside temperature was 6C. I left the covers of the headlights open, to let them dry. The covers were left open a day or day and a half. After this i sealed the covers (again with hand cream) get them closed and for now, i had no condensation jet. I did this three days ago. It is still pretty dry ( 40%) and cold (6C). On Friday will start raining, and than i will have all the answers. But from theoretical point of view, i thing this last method has good chances to work. Will keep you posted.
One more word about sealing.
What is the point of sealing, if there is a ventilation valve (that grey square thing on the edge of the headlight, right where the blinkers are). Sealing/resealing is only when the rain/water is entering inside the headlamp.
Hope it helps, cheers, Andrej