What we're talking about here, simply put, is vehicle conspicuity. This is a topic well researched in the Emergency Vehicle arena. There is a study I'll post a link to below about this topic, although this study focuses on conspicuity of Emergency Vehicles primarily stopped, such as at the scene of a wreck or similar location. Further, let me post just one section of the study right here, which talks about bright lighting:
The “Moth Effect”
There is limited scientific evidence to support the notion that drivers steer toward bright lights, such as
those used to increase the visibility of emergency vehicles, as “moths to a flame" (often called the “moth
effect” and technically, “phototaxis”). (Interview with Dr. Michael Flannagan, 2008; Green, 2009) Several
recent studies, however, suggest that while bright lights may not be the cause, drivers' fixation on roadside
objects can cause their steering to drift in the direction of their gaze. (Readinger et al., 2002; Chatziastros et
al., 2006) This effect may be more pronounced with other impairments. The implications of these findings
on emergency vehicle visibility/conspicuity are unknown, but certainly support the need for additional
research on how to design passive conspicuity treatments so they draw drivers’ attention enough to induce
the appropriate (“stay away”) response, without causing the potentially negative results of visual fixation.This is not to say that a motorcycle with a bright headlight will cause this Moth Effect, but it's interesting all the same, and again, they're primarily talking about emergency vehicles parked at scenes.
I can tell you from the experience of sitting in the cab of a moving Emergency Vehicle with a lot more lights going than a motorcycle headlight, is that drivers don't often see those vehicles either, just because the lights are engaged. However, for certain, the lights flashing in varying pulses, such as programmable LED warning lights affixed to all surfaces of the vehicle, certainly make a difference. Back in the day of incandescent lighting, we were thrilled with Whelen and other warning device manufacturers came out with strobes. Studies back then showed that a combination of incandescent and strobes offered the most conspicuity for emergency vehicles. This would tend to support and advocate the use of a headlight modulator on a motorcycle, which provides that pulsating light pattern.
Light colors are also addressed somewhat in the study I referenced. It's interesting to note, but not surprising, how lighter colors such as amber and white, attract the most attention. Another plus for the flashing headlight position.
You may have noticed yourselves just how far away those amber lights of DOT or "Road Ranger" vehicles get noticed when you're hurtling down the interstate at sub-light speeds. In Florida, the statute changed a few years ago to allow commercial and other work vehicles (passenger vehicles, pickups, etc.) to sport flashing white lights. These originally were only allowed in Emergency Vehicles. They definitely catch your attention; yet another +1 for a modulating headlamp.
The net result here, I believe, is that
combinations of lighting facilitates the most conspicuity. Since we can't bolt on flashing LED's facing forward, at least, it stands to reason that the pulsating headlamp on a motorcycle is probably the best way to achieve the most forward facing conspicuity. Will a solid high-beam light do the same thing? In my opinion, no, and for obvious reasons. If solid, non-flashing lights promoted conspicuity, they'd be on Emergency Vehicles -- and WERE for many years, a long time ago.
Take a look at the conspicuity report, because it addresses the science around "retroreflectivity," which is what you're dealing with when you paste reflective decals and such onto your bike. The study shows that reflective markings are definitely a plus at night, and may very well be worth adding to motorcycles, as many have already done.
And just some additional food for thought -- someone mentioned the loud pipes debate again. This is another area of Emergency Vehicle warning that I can tell you about. Emergency Vehicles, at a minimum, will have at least one 100 dB forward facing audible warning device, in the form of a speaker (driver) or perhaps a mechanical siren like a Federal "Q" type. Most nowadays, have several, emitting varying tones and frequencies. That, along with air horns and the like, can generate many hundreds of dB's. The problem is, at 40 mph, the "effective range" of a siren is about 300 feet. At 60 mph, that range decreases to a mere 12 feet. Add in the ultra-quiet cabins of modern vehicles, especially the luxury marques, and that range may be lower. So loud pipes simply aren't going to do anything to warn anybody of a motorcycles approach, especially since the pipe is facing rearward. This is not to say that they don't attract attention laterally, such as when a bike is overtaking a car. That debate rages on and will continue to do so, for sure. Loud horn modifications on motorcycles may help in some circumstances, more likely at slower speeds, but falls under the same science. At a higher speed, the effective range decreases, period.
http://www.iaff.org/hs/evsp/USFA%20Emergency%20Vehicle%20Visibility%20and%20Conspicuity%20Study.pdf
