When drivers are asked what they look for in car lighting, “brightness” is one of the top answers. A large range is similarly popular. Further frequent responses include the color blue and LED as the light source. Homogeneity, on the other hand, is rarely mentioned. This is probably partly due to the abstract nature of the term itself (the general meaning of which is explained here). The relative indifference, however, also extends to the much more familiar term of uniform illumination.
Despite these results, homogeneous (or uniform) light distribution is a key characteristic of good headlights, helping drivers to detect obstructions on the road much more quickly than would otherwise be possible. When the light distribution is uneven, it’s possible for potholes or other dangers to “hide” for vital fractions of a second in a poorly illuminated area ahead. Although visible again an instant later, this delay may mean it’s no longer possible to avoid them.
Two-fold increase in safety
Uneven (or inhomogeneous) distribution of light also places a greater burden on the eyes and brain. They need to do a lot more work to compensate for the differences in brightness and distinguish details in the darker areas. This extra effort has a tiring effect on drivers. Homogeneity can therefore be seen to have a two-fold benefit on traffic safety – helping obstacles to be detected more quickly and reducing the risk of driver fatigue.
Over the past few decades, every innovative lighting technology has had a positive impact on homogeneity. As a rule, greater luminous flux leads to a more uniform lighting distribution. This is why the advent of xenon light in the early 1990s brought such a dramatic improvement, delivering around three times as much light as the previously standard H4 lamp. When reflectors or lenses are correctly configured, xenon headlights are able to evenly illuminate an extremely wide section of the road. Only the latest generations of LED headlights have been able to challenge xenon’s preeminent position. The older models provided less luminous flux, meaning developers were forced to concentrate the available light into crucial areas.
Chess boards on the road
In point of fact, this whole topic involves a conflict of goals. Achieving homogeneity and range at the same time is not at all easy to accomplish, particularly when (unlike in xenon headlights) there is no abundant amount of light available. When LED technology is used, individual light-emitting diodes can be utilized exclusively for range and others to compensate for differences in brightness. Results can be impressive, depending on the effort (and expenditure) invested by the makers.
The conflict of goals is most apparent in some matrix headlights with a glare-free high-beam function. These have an extremely large number of LEDs, each of which illuminates only a particular part of the road. However, in the first such systems to hit the market, the difference between adjacent LEDs was easily noticeable, resulting in what experts refer to as the “chessboard effect”.
But enormous progress has been made since then, mainly due to the explosive increase in the number of pixels. Volkswagen recently presented an experimental headlight with LCD HD technology . In terms of homogeneity, they leave practically nothing to be desired.
But those wishing for homogeneous light don’t need to wait around two more years for this innovation to enter production – or even go out and buy a new car. With halogen and xenon headlights, a lot depends on the lamp itself. The more precisely the filament or arc is positioned in the focal point of the headlight, the better and more evenly the light can be distributed. Although there are guidelines that regulate this, there are also permissible tolerances – and, regrettably, manufacturers that fail to comply with either. Lamps from a premium manufacturer like Osram meet even the most stringent regulations. In doing so, they contribute to providing the greatest homogeneity the various headlight technologies are capable of delivering.