The invention relates to a light comprising a light source or connection means for a light source, and a transparent panel which extends crosswise to a direction of light emission. The concentration of the sulfur component contained in the reducing agent added by the reducing agent adding unit is lower than the concentration of at least the sulfur component contained in the fuel supplied to the combustion chamber of the internal combustion engine. Also methods for retarding the accumulation of dental plaque andor calculus are provided. The switch that provides the differentially switched high-voltage output signal includes two differentially coupled chains, each having at least three serially coupled FETs.