While this feature focusses on the main headlamp bulbs, the advice on filament lamps is relevant to other exterior lamps, too
The light source Replacement car bulbs remain one of the fastest moving and profitable product lines, leading Rob Marshall to question Osram and Philips Lumileds about how they work and why they degrade It is quite remarkable that the humble light bulb has become so central to our modern way of life that we take the technology for granted. While conventional bulbs were banned from domestic use from September 2021, they remain popular within an automotive context. The principle on which a halogen bulb works extends to the early 1800s. Humphrey Davy discovered that a metal wire heated up, when electricity passed through it. Unfortunately, the wire reacted with the oxygen in the air and burnt away; enclosing the wire within a glass tube containing inert gases posed the solution.
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Modern automotive bulbs employ coiled tungsten filaments, because the metal possesses the highest melting point. The use of halogen gases extends the filament's life, because any evaporated metal redeposits itself onto the filament, increasing its life. Naturally, the bulbs do not last forever, chiefly because the filament thins and, eventually, fractures. While all automotive replacement bulbs, used in exterior lamps, must be Type-Approved, quality still varies between manufacturers. Some bulbs possess thinner filaments, less
expensive gases and lower quality glass. The gas fill pressure can also be too low and poor quality production can also introduce impurities into the glass envelope. Low grade bulbs can also damage the lamp to which they are fitted. Should the bulb glass lack an ultra-violet filter, the UV can damage the reflector and plastic cover. Some bulbs can also shatter, due mainly to thermal shock, especially if water enters the lamp unit for any reason, although those featuring quartz glass should be immune. Yet, technicians can also facilitate failure. Touching the bulbs with bare skin can impart an impurity that creates a hot spot. In addition, badly-fitted bulbs can increase their exposure to vibration and, possibly, overheating.
