what sealant needed for lights that are steaming up?
 

as above

Front? Rear?

If they steam up regularly, they probably have moisture in them, so it's important to get rid of it first, then seal them.

Get rid by placing them without bulbs, bulb-hole upwards in an airing cupboard overnight. A day in the freezer helps too;)

You can seal them with Tiger seal, Sika-flex or Carafax non-setting mastic.

I'd not use silicone, as it's not meant to be immersed regularly.

Alcazar