We compared the visual conspicuity of several different types of modern bicycle lights to the conspicuity of some conventional lights, for several relevant trafic secenarios, for different ambient lighting conditions, and for different ways of mounting the lights. We only investigated the detectability of the lighting, becaue this crucial traffic safety issue. Factors like identifiability and distance estimation were not studied.

For front lights we find:

• Without flicker some of the tested modern front lights are significantly less conspicuous, and others are significantly more conspicuous, than the conventional front light that served as a reference.
• The conspicuity of a front light  that shines straight ahead is independent of the way in which it is mounted (i.e. whether it is attached to the bicycle or attached to clothing)
• The conspicuity of a modern front light that is not mounted straight (i.e. diagonally, vertically, or slanted) is usually less than the conspicuity of one that is mounted horizontally.
• For a straight posture of a cyclist a lamp attached to the chest is visible in the entire forward sector.
• A bent-over/slanting posture can decrease the sector in which the lamp can be seen with more than three times. A bent-over postur als causes the lamp to slant. Since most lamps radiate strongest (have highest luminance) in the forward direction, a slant will also cause the lamp to appear less bright, and therefore less conspicuous.
• In most cases flicker raises the conspicuity of front lights.
• There is no clear relation between flicker frequency and conspicuity.

For rear lights we find:

• Without flicker all tested rear lights are just as, or even more, conspicuous than the conventional rear light that served as a reference.
• The conspicuity of a rear light that shines straight ahead is independent of the way in which it is mounted (i.e. whether it is attached to the bicyle or attached to clothing).
• The conspicuity of a modern rear light that is not mounted straight (i.e. diagonally, vertically, or slanted) is usually less than the conspicuity of one that is mounted horizontally.
• Flicker does not contribute significantly to the conspicuity of rear lights.

Other conclusions:

• Norms can be defined for the conspicuity of bicycle lights in a given environment, and the corresponding functional requirements for their luminous intensity canbe formulated.
• There is no need to increase the conspicuity of front light by using flickering bicycle lights:
  - Flickering bicycle lights make it harder for the other road users to estimate the speed and trajectory of a bicycle.
  - Flickering bicycle lights may reduce the conspicuity of emergency services.

Recommendations:
- Front bicycle lights should be white.
- Bicycle lights should not flicker.
- When attached to clothing, bicycle  lights  should be visible at all times.
- The importance of proper ways of attachment and alignment should be communicated to the users.

The importance of an isotropic radiation characteristic should be communicated to producers and dealers.