Do fly killers need black light or black light blue types of light bulbs?

Fly killers also known as bug zappers use UV light to attract insects,  Both black light and black light blue are types of UVA light but the commonly used UV ln fly killers is the standard black light.

These UVA bulbs emit a wavelength of between 350-370nm and are highly attractive to flying insects.

Understanding UVA light in insect traps

UVA often called black light is important as insects are sensitive to this spectrum which draws them into the traps killing grid or glue boards.

Black light (BL) lamps

These are the most common tubes found in fly killers.  They email UVA light along with some visible blue light. These run at 350-370nm which is the peak attractiveness for flying insects.

Black light blue (BLB) Lamps

BLB lamps are normally dark blue/purple in colour and technically produce black light and they are often used for theatrical or forensic purposes as they make fluorescent material and white colours glow brightly.  They can be used in fly killers but generally it is the standard black light that is used.

Why are bug zapper lights blue?

The light emitted from fly killers is not truly blue to insects, it is the invisible spectrum that attracts them.  To the human eye these lamps appear to have a deep blue/purple glow for 2 reasons

1.  Manufacturing necessity - the glass envelope of the tube contains phosphors that convert UVC light (produced by the mercury arc inside the tube) into the required UVA.  During this process some of visible light is emitted and this falls into the blue hue end of the visible spectrum.
2.  Visual Confirmation - The bluey colour is used as a visual indicator for people that the bulb is functioning in the correct UV range.

Why is my fly zapper not attracting flies?

If a fly zapper is not attracting the flies is it normally due to:-

1.  Old or worn out bulbs - it is recommended that the tubes are changed yearly and ideally before the peak fly season.  The peak performance for these tubes once fitted is 0-6 months,  declining attraction is between 6-9 months and between 9-12 months they are becoming ineffective.
2. Competition from natural light - Insects are attracted to the strongest light source in the room.  If you place your fly killer near a window or a brightly lit lamp  it will become weaker  as the UVA light will be overwhelmed by either brighter or more natural light
3. Improper placement - the fly killer should be placed away from entrances, any where that people are congregating  and it should ideally incept insects before they can enter a kitchen or dining area

Height - Optimum height for fixing the fly killers is between 5 and 6 feet from the floor

Food and odor - If the zapper is placed next to food or strong odors it will distract from the light attraction.

4. Poor maintenance - If the fly zapper’s killing grid or glue board is full of insects it would render the tube ineffective as the dead insects shield the UVA light required
5. Incorrect bulb type - Using a standard fluorescent bulb will have no effect on the attraction of insects as the light spectrum will not contain the wavelengths the insects seek.