What is BLACK LIGHT?
BLACK LIGHT refers to /BL.
Ballast (usually). Otherwise, on non-Ballast lamps /BL usually means Blister Pack, but, in some instances on filament bulbs might indicate "blue" light output.
On wide spectrum (unfiltered) UV output fluorescent bulbs /BL means "black-light"; who's bulbs are WHITE color when OFF. Fluorescent UV narrow filtered bulbs which are BLACK (dark purple) when OFF are actually /BLB "black-light blue" bulbs.
references for this page: /BL, BLACK-LIGHT, BLACK-LIGHT BLUE, BLACK LIGHT, BLACK LIGHT BLUE
references to this page: /BLB, ULTRAVIOLET