In spite of halogen light and LED-lights, a number of
vehicles will still be fitted with light bulbs. They are relatively reasonable in price, need no pre-resistor and replacements are found almost all over the world. At least as far as durability is concerned, the light bulb can
compete against the halogen light. If it is not exposed to too much, and too sudden vibrations, it can give an average service life of approx. 200 hours of operation.
The filament wire is made of Wolfram, which has a very high melting pont of 3380°C. Of course, under normal circumstances this temperature is not reached. If one measures the resistance in a cold light bulb, using
the formula U = R x I und P = U x I the specified performance is not given. This is due to the cold resistance, which only offers one tenth of the resistance of when the light bulb is switched on. This of course, also has
an influence on the current intake. Almost any electric tool (e.g., a sanding machine) which, when in operation, has a current intake distinctly lower than 16 A, can cause any (household) fuse to trip out the moment the
tool is switched on. For this reason they are mostly fitted with an electrical-surge-limiter. Because of it's resistance behaviour, a light bulb can well be serially switched together with a battery that is to be charged. The
initial high voltage drop in the lamp sinks with the charging time, thus providing a constant charging current.
In the above picture a two-filament lamp is shown. To save space, it is still always used in the rear
lighting system for the brake-light (21 W) and the rear light (5 W). It has two pins at different heights on the side, so that when being installed, the two (differing) filament coils always have the correct contact. If for
design reasons the light-glass is transparent, then the bulb-glass must be coloured according to it's function.
When being fitted, the glass part of the bulb should not be touched with the fingers because grease and much more the salty sweat from the skin attack the glass and can cause it to crack and possibly also dull the