This Bulb has a Black/Blue coating inside the tube to filter out the white light for ambiance as well as correct range of UV. The intensity of the UV emitted         diminishes over time - we recommend you change the tube every 24 months.

WHICH IS THE BEST TUBE TO USE, BLACK OR WHITE?

• They are both UV Black Lights. The white (BL) one gives off a brighter light and it’s only humans that see them differently.  
• The black (BLB) is a much deeper purple light.
• It doesn't really make that much difference as the biting insects see them both the same.