Philips TUV PL-L 18W/4P Germicidal Light Bulb Security of effective disinfection over the useful lifetime of the lamp. High system efficacy because it is not required to over-design the purification system to maintain effectiveness of disinfection. Protective inside coating ensures constant UV output over the complete lifetime of the lamp. Good environmental choice because of lowest amount of mercury. Beware of Counterfeits - Buy only from Authorized Dealers.