Solution

Convex mirrors are used as reflectors in sodium reflector lamps because they are able to spread the light over a wide area.  The neon gas  lights at a lower temperature. As the temperature increases the  sodium begins to vaporize and the  lamp turns to a pure yellow. Argon has a lower glow voltage, argon helps the smaller  lamps start at a lower voltage. The larger LPS lamps used in street  lighting for the most part do not use argon.