A tensioner for a power transmission system includes two tensioning arms operatively engaged with the strand of the chain or the belt of the power transmission system. The optical unit includes a reducing portion which is directly provided in a illumination light emitting portion or provided frontward to part of the illumination light emitting portion and which reduces the density of the primary light as the illumination light emitted from the illumination light emitting portion. The bundled financial instrument may include any set of contracts considered a linear combination of a plurality of standardized contracts associated with an obligation to exchange an asset at a set price on a future date.