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Paul Moore and David Kerns of the US want to help tennis players and
spectators at matches keep their eyes on the ball (W0 98/26326). The players use
yellow tennis balls which have been treated with a fluorescent dye to make them
glow in ultraviolet light. This comes either from natural sunlight, or
UV-enhanced indoor lamps. Players and spectators can wear special glasses, or
spectators can watch the game through a treated glass panel at the front of a
stadium. In each case, the glass has a transmittance peak that is centred on the
blueish light coming from the balls. So the balls glow brightly to the people
watching.