The square of the hypotenuse is equal to the sum of the squares of the other two sides – known as Pythagoras‘ theorem, this mathematical formula is still familiar to most people from their geometry lessons at school. Not many of us, however, would ever have seen any connection with automotive lighting. Nevertheless, geometry plays a key role in headlights. Alongside luminous flux it’s the most important factor of all.


In order for a headlight to deliver its light accurately to the correct areas of the road, the geometry of the filament needs to comply precisely with the specifications. In other words, the glowing portion of the coiled tungsten wire must be positioned in the focal point of the reflector. This can only be achieved by ensuring its location and the distance from the base are absolutely correct. Only the smallest of deviations (hundredths of a millimeter) are permitted. Alongside distances, angles are important as well.


End-to-end control

At Osram, the dimensions and tolerances of every single lamp are checked at several stages in the production process. A particularly critical part of the manufacturing process for a halogen headlight lamp is the point at which the glass envelope containing the filament (or burner) is joined to the metal base. Before the assembly machines place the final weld spots, the position of the filament is measured in three axes.


Quality saves money

This level of care and attention costs money – money that not every no-name manufacturer is willing to spend. The upshot: a no-name lamp’s inner workings can deviate from the specifications by as much as an entire millimeter. In comparison, tolerances for Osram lamps are in the hundredths of a millimeter range, and so clearly below the deviations permitted by relevant regulations.

But this level of precision definitely pays off. When the geometry is correct, the headlight can be adjusted with complete accuracy. What’s more, when a headlight lamp from a reliable brand is replaced by one of equal quality, there’s usually no need for any readjustment. This means purchasers actually save more money than they would have by buying a no-name product instead of a quality bulb.

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