Tube lights typically use a mixture of argon and mercury vapor. Here's how it works:

* Argon acts as a starter gas. When electricity flows through the tube, it ionizes the argon, creating a plasma that helps to initiate the discharge.

* Mercury vapor is the primary light emitter. When excited by the electrical discharge, mercury atoms release ultraviolet (UV) radiation. This UV radiation then strikes a phosphor coating on the inside of the tube, causing the phosphor to emit visible light.

So, while the argon gas gets the process started, it's the mercury vapor that's responsible for producing the UV radiation that ultimately creates the light we see.