hi all,

 

just a general question I've been pondering...

 

does anyone ever get their sidelight or numberplate light bulbs getting a shiny blackish silver coating on the outside, leading to reduced brightness? I've noticed it on a couple of my car's bulbs (and have ordered replacements) and have certainly noticed it on several other cars I've had

 

I've never seen bulbs for sale with this effect so I can only assume that it's due to dirt or grease colouring them, or perhaps that they'll soon fail, does anyone know what produces it? I've done plenty of googling but of course all I can find is references to cloudy headlights 

20 minutes ago, hebdenwill said:

hi all,

 

just a general question I've been pondering...

 

does anyone ever get their sidelight or numberplate light bulbs getting a shiny blackish silver coating on the outside, leading to reduced brightness? I've noticed it on a couple of my car's bulbs (and have ordered replacements) and have certainly noticed it on several other cars I've had

 

I've never seen bulbs for sale with this effect so I can only assume that it's due to dirt or grease colouring them, or perhaps that they'll soon fail, does anyone know what produces it? I've done plenty of googling but of course all I can find is references to cloudy headlights 

The lamp is on its way out, it'll probably fail soon.

 

The shiny black coating is actually on the inside and produced by the deteriorating tungsten filament.  

 

In small low voltage "vacuum filled" lamps the glass envelope is too close to the filament and tends to get blackened over time with the continuously evaporating tungsten filament.   The filament usually burns out before the blackening effect really takes place, but it does show the lamp is on its last legs.

 

But best to change them as soon as you get your replacements in.

 

Thank you, very well explained! I'll change them out as soon as the new bulbs arrive