While your current Insect killer bulbs may be still emitting visible light, after a period of approximate 4000 hours of run time the amount of UV light emitted by a lamp will have dropped to a level where it will not be effective at attracting insects. Therefore it is advisable to replace the tubes in your insect zapper yearly, even if they lamps appear to still be admitting plenty of light as the useful UV light is not visible to the naked eye
These tubes are suitable for a variety of brands of insect zappers which take T9 round 22W circular UV tubes such as Insect-o-cutor Select SE22, SE44, CG22, CG44. Insect-a-clear F10CSW & F10CSS