UNDERSTANDING BEAM PATTERNS
IT'S NOT ONLY ABOUT POWER ... IT'S  ALSO ABOUT CONTROL
 
     
SourceFlickr: The Commons. Photo on the left initialed "J. Lemm" (ca. 1910-15) forms part of the George Grantham Bain Collection (Library of Congress). Photo on right (ca. 1882) was photocopied by: Dave Conner.

If you have driven a car and ridden bicycles with modern high powered lighting you probably already noticed a difference between the beam patterns they produce. Modern incandescent automotive headbeams produce roughly 1000 to 1500 lumens of light, which is roughly amount of light produced by modern high powered LED lighting systems for bicycles. When driving a car however, you probably notice that the “carpet” of light on the road surface is relatively even and reaches much further ahead than that of a typical LED bicycle light, even where lumens ratings are similar. This is because very few bicycle light manufacturers have to date invested in optics to sculpt beam patterns for optimal efficiency … and safety.


STANDARD BICYCLE LIGHTING BEAM PATTERN
Standard bicycle lighting optics are largely borrowed from flashlights. The result of such beam patterns is normally high intensity light near the cyclist that dilutes very quickly as the distance on the road ahead of the cyclist increases. In many ways, this is the reverse of what a cyclist needs which is more light intensity further away from the bicycle and less near the cyclist thus creating a homogenous carpet of light reaching far ahead of the bicycle. An ideal beam pattern is one that illuminates imperfections in the road well ahead of the bicycle thus allowing for the cyclist to track them under consistent brightness as the bicycle approaches so the cyclist can avoid them.


THE STANDARD AUTOMOTIVE "DIPPED" BEAM
It is with these considerations that automotive lighting and the regulations governing them have evolved over the past half-century. Automotive lights are required to produce “dipped” beams with a strict horizontal “cut off” at the top of the beam pattern designed to protect oncoming traffic from glare. The reflector is furthermore actually designed to spread light as homogeneously as possible on the road surface ahead of the vehicle. Indeed, automotive dipped beams are actually very sophisticated in their use of the light produced as can be seen below.  

        
Source: Wikimedia Commons. Photo on left by: Scoo. Graphic on right by: Ruizo.


OPTIMUM OPTICAL DESIGN FOR CYCLISTS
If cyclists had the option of similarly powerful lighting systems on a bicycle used in road based applications, it would make sense for them to utilise automotive beam pattern standards that have evolved over half a century of use and refinement to optimise user-friendliness and safety. In can be seen in the graphic above that the asymmetric beam pattern is purpose designed to reduce glare for oncoming traffic (on the left of the automobile) while optimising the reach of the lighting directly ahead. The safety and efficiency of the modern automotive headbeam did not happen by accident. It would be sensible for such technology to be incorporated into bicycle headbeams.

It is of course intuitive that cyclists would consider brighter to be better as they are more vulnerable road users. The advent of LEDs have today made accessible to cyclists lighting system producing many more lumens of light output than automotive headbeams. As such powerful bicycle lighting systems become increasingly common, a scenario of bicycles regularly projecting the equivalent of automotive highbeams on public roads is an impending possibility. It is not clear that such a scenario increases the safety of cyclists. Being noticed is important, but situations where oncoming traffic is blinded by lights from bicycles are unlikely to increase the safety of cyclists, particularly those blinded by other cyclists.

 

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