When you hear a light being described as “black light” and “black light blue” it is not immediately obvious what the difference between these two things would be.  The confusion between these terms is fairly common and there are a few key differences meaning it is important to know the differences if you need to replace this type of light.  

The difference between these two terms is:

• Black Light Blue: This is the scientific term for electromagnetic radiation that has a wavelength shorter than visible light but longer than X-rays. UV light is invisible to the human eye.  You would use this for a fly killer unit for example.
• Black Light: This term is used for a lamp that emits a long-wave UV light (UVA, typically 315 nm to 400 nm) while minimising the output of visible light.   This makes fluorescent or light coloured materials glow without illuminating the rest of the room brightly.

What are the other differences between Black Light and Black Light Blue?

The distinction between these two types of light can be found in the glass envelope or filter material used.

1. Black Light (BL)

The standard "black light” is a fluorescent tube or lamp that emits UV radiation.  It uses a glass that is specially treated to absorb most of the light which is done by giving it a phosphor coating.  These lamps are often used in fly killer units designed to attract insects.  The tube itself is clear and the light once turned on may have a faint purple glow.

2. Black Light Blue (BLB)

"Black Light Blue" is often used for parties, theatrical effects and can even be used for currency verification.  It is designed to maximise the fluorescent visual effect of the items it is shining upon making items such as white clothing glow brightly.

The "blue" in the descriptor for this type of light refers not to the color of the filter rather than the light itself.   These lights use a dark violet or deep blue filter glass which is made from a barium-sodium silicate glass.  It allows the long-wave UVA light to pass through and blocks almost all other visible light produced from the tube.  When it is turned on it appears as dark purple/blue.  

Is there a difference between a Black Light and a UV Light?

A black light is a type of UV light, to be specific it is a UV-A light.  This also applies to black light blue lights as well.  UV light is the scientific classification for an entire range of electromagnetic radiation based light that is invisible to the naked eye. This category can be divided into three types:

• UVC (100–280 nm): Short-wave light that is mostly used for germicidal and disinfecting purposes. It is extremely dangerous to human skin and eyes.
• UVB (280–315 nm): Medium-wave light that can cause sunburn and is used in some medical treatments.
• UVA (315–400 nm): Long-wave light which passes through glass more easily and is used for fluorescent effects and tanning.

In Conclusion

"Black light" is the term used to describe a lamp or lighting fixture specifically designed to emit UVA light (315-400 nm).  “Black light” is used to make highlight fluorescent colour and/or materials in an object whereas “Black light Blue” lights are designed for use in a fly killer unit.

All black lights can be described as UV lights but not all UV lights are black lights.  Black lights are UVA lights - anything else would be just a UV light (UVB or UVC).  A UVB or UVC light will never be described as “black light” or a “black light blue light.”