There are incandescent, low pressure sodium, high pressure sodium, low pressure mercury, high pressure mercury, metal halide, and LED street lights.
- Incandescent street lights: They are used in the earlier centuries, but because of the high energy consumption, people don’t use them anymore.
- Low and high pressure sodium street lights: Low and high pressure sodium lights stimulate the sodium vapor to emit light. They have a relatively high efficiency and low CRI.
- Low and high pressure mercury street lights: Similar to sodium street lights, the mercury vapor in them emits light. Low and high pressure mercury street lights are cheap, but will cause pollution.
- Metal halide street lights: These lights have higher CRI, but the metal halide is unstable.
- LED street lights: Many countries are changing their lights into LED ones because they have a high efficiency and CRI.
More reading: 7 Types of Street Lights Classified by Light Sources