Although the tubes in your fly zapper may appear to be working and giving out plenty of visible light after use of around 6000 hours run time the amount of useful insect attracting UV light coming from your old lamps drops to a level where it will no longer be attracting insects to your bug killer These Replacement UV blacklight bulbs for bug killer machines fit 15 Watt/30 Watt fly zappers that use 300mm T5 bulbs such as the Pestwest Titan Alpha

Specifications:

• Wattage: 15w
• Bulb length: 30cm / 12 inches
• Weight: 60g
• Average life: 6000 hours
• Cap type:  G5
• Quantity: 2 tubes
• Type: T5

Please check the size of the bulbs that your zapper takes before ordering. As these tubes are 12 inch / 30cm in length. 

It is also advisable to replace the starters in your insect killer when replacing the bulbs as your old starters may not be able to provide enough power to reliably light your new lamps