Elsewhere on this site are diagrams showing the beam performance of various headlamp units. Why not photographs? Because photographs of beam patterns can be very misleading even if the photographer has the best of intent. That's because pixels and film work in a fundamentally different way than human eyes. Even a photographer who tries very hard to keep all the camera settings identical when photographing different beams up against a wall cannot present more than broadly general information about the beams, and then only by comparison (a sharper cutoff vs. a fuzzier one, for example, or a wider beam vs. a narrower one). To determine the safety performance and other aspects of any headlamp's output, we need to look at objective, quantified data that can't be had from photographs. The way to do that is with isocandela diagrams, which are generated by a machine called a photogoniometer that measures the intensity of light produced by the headlamp through a large range of vertical and horizontal angles.

The diagrams are just like topographical (elevation) maps, except the contour lines represent levels of light instead of elevation above or below sea level. The beam pattern is correctly aimed as it would be on a car on the road, and each contour line represents the threshold of a particular intensity level. Each diagram is plotted on a chart calibrated in degrees. Straight ahead is represented by (0,0), that is, zero degrees up-down and zero degrees left-right, which is at the centre of the diagram.

To get an approximate "feel" for the units and amounts of light under discussion here:

The main parameters to pay attention to when looking at the diagrams are:

Click here for the 165mm x 100mm small rectangular headlamp diagrams

Click here for the 7-inch large round headlamp diagrams (which can be used to compare, brand-for-brand, the 200mm x 142mm large rectangular headlamps, too)

Click here for the 5¾-inch small round headlamp diagrams