The most common type of lighting unit utilized in street lighting is:

a. metal halide lamps

b. mercury vapor lamp

c. high-intensity sodium vapor lamp

d. incandescent lamp

Option C. The sodium vapor lamp is a gas discharge lamp that uses sodium vapor for the production of light. It is an efficient lighting source that provides lumens per watt and produces bright yellow. It has a monochromatic light that makes its applications are reduced. It is used in street lighting, streets, highways, etc.