Andy, I would guess that on a 2005 car your headlamps are not totally sealed as per the description by RRSTDV8 above.

Changing bulbs in a low humidity area would not make any difference if once fitted in the headlamp it is in any way exposed to the air. Its just going to gain moisture from the environment especially with this current weather. So if it has a drain tube or similar, then it will naturally gain and lose moisture via that drain tube. So it would seem that its only if the headlamp is sealed that the low humidity environment should be considered when changing a bulb.

For those of us with pre-facelift cars it might be worth checking that that drain tube is clear to do its job...  Robin
2008 Range Rover Sport TDV8
Gone:
Jaguar S-Type V8 4.2 Sport
MGZTT 190 2.5

Think I might try some silica gel sachets in the light unit over the next couple of days whilst the car is not being driven to help remove the moisture as it certainly doesn't seem like normal operation of the lights is going to dry out the inside of the light unit sufficiently. Range Rover Sport 2010 3.0 TDV6 HSE in Black
103,000 miles and a BAS Remap

Last edited by Chunk11 on Wed Jan 03 2018 8:11pm. Edited 1 time in total

In the 80's and 90's we used the completed seal headlights.
Once water got in, it would stay in

More recently we have these vents/tube loops/membrane or even open which are generally much better on the whole. You do get a bit of mist, but it usually quickly sorts itself out

I am hoping if I can remove a lot of the moisture then that will solve the issue but will keep you updated. I think there maybe too much moisture for the natural venting system to handle so I am thinking if I can get as much as I can out then hopefully the light unit will be able to handle what is left?! Range Rover Sport 2010 3.0 TDV6 HSE in Black
103,000 miles and a BAS Remap

Right all set for tomorrow’s test. I have a rather large number of silica gel sachets and have tied a piece of string so I can retrieve them easy enough. I was going to try it this morning without but realised I could only just about fit my hand down the back of the light unit.
 Range Rover Sport 2010 3.0 TDV6 HSE in Black
103,000 miles and a BAS Remap