This article is from the Bicycles FAQ, by Mike Iglesias with numerous contributions by others.
From: Jobst Brandt <email@example.com>
Reflective tape is available in most better bike shops in various
forms, most of which is pre-cut to some preferred shape and designed
for application to some specific part of the bike or apparel. The most
effective use of such tape is on moving parts such as pedals, heel of
the shoe or on a place that is generally overlooked, the inside of the
First, it is appropriate to note that car headlights generally produce
white light and a white or, in fact, colorless reflector returns more
of this light to its source than ones with color filters or selective
reflection. Red, for instance, is not nearly as effective as white.
Placing reflective tape on the inside of the rims between the spokes
is a highly effective location for night riding because it is visible
equally to the front and rear while attracting attention through its
motion. It is most effective when applied to less than half the rim
in a solid block. Five inter-spoke sections does a good job. One can
argue that it isn't visible from the side (if the rim is not an aero
cross section) but the major hazard is from the front and rear.
Be seen on a bike! It's good for your health.