A method and apparatus for treating a fluid. The spread spectrum signal includes a reference signal and a message signal. In each layer of the light emitting part 4, a hydrogen concentration is not more than 2\xd71017 cm\u22123, a carbon concentration is not more than 2\xd71016 cm\u22123, and an oxygen concentration is not more than 2\xd71016 cm\u22123. The planar portion and the mounting flange have respective ceiling-facing or wall-facing surfaces, which may be coplanar, which may be parallel but not coplanar, or which may be oriented at a right angle relative to each other or at another angle relative to each other.