[0054] Triboluminescence is an optical phenomenon in which light is generated or emitted by a material when that material is subjected to a force, stress or strain. The force or stress may result from contacting the triboluminescent material with another object such as when a golf club head strikes a golf ball. Other types of contact may be described as scratching, crushing or rubbing. Although not bound by any theory, it is believed that the light generation may come from the breaking of bonds in a crystal or the application of a mechanical shock sufficient for certain electrons to overcome their energy barrier and cascade down to ground state.

[0002] An ongoing frustration with sports enthusiasts is the ability to track and find athletic balls such as golf balls, tennis balls or baseballs, particularly in low light conditions that exist at dusk or at night. For example, in low light conditions it can be difficult to observe a golf ball in flight after it has been struck by the golf club head. Even more frustrating is the inability to find a golf ball that is lying in a concealing location such as deep rough or plant undergrowth. Thus, a ball that is easier to track in flight and locate would be desirable.

[0003] Non-white golf balls have been made, but such balls typically have a color that is either always "on" such as with a pigmented or fluorescent ball. Other balls have been disclosed that reversibly change color, but in response to environmental stimuli such as sunlight, temperature or water. A reversible color-changing ball that is not dependent upon uncontrollable environmental stimuli would be useful.

[0047] A triboluminescent ball according to the present disclosure generates light when the ball is struck by another object such as the head of a golf club. The triboluminescence then dissipates or fades over a certain time period with the ball eventually returning to its original color. When the ball is struck again, the triboluminescence is again generated. In contrast, in other types of luminescent golf balls (e.g., fluorescent) the luminescence is always "on". In other words, the luminescence or light generated by the ball does not dramatically change over a short period of time. Moreover, a triboluminescent ball does not undergo a color transformation in reaction to environmental stimuli such as sunlight, temperature or water. The triboluminescence generated by the ball upon contact is useful to visually trace the ball in motion (e.g., its flight) and at rest (e.g., for finding the ball in long grass). Moreover, the amount of generated triboluminescence can be adjusted so that it varies depending upon the strength of the force applied to the ball. For example, the amount of generated triboluminescence could be relatively low or non-existent when a weak force is applied to the ball such as during putting. Due to the triboluminescence, the golf ball can reversibly change color upon application of a force or impact to the golf ball.