Before Led light come to the market, the high pressure sodium(HPS) lamp is not bad, such as HPS for road lighting has the following advantages and defects:
1. Advantages:

•  Low color temperature yellow light, rain and fog weather, strong penetrating power.
• Power can be done relatively large.
• Small volume, light, strong wind resistance
•  Lamps with relatively low price.

• Huge energy consumption, bad power efficiency. For example, usually nominal 150W HPS, its overall energy consumption measurement generally more than 217W, the power efficiency is only 66.8%.         
• Very low color rendering index, Ra usually only around 20-30, the light is dark, color rendering ability is bad. It is very bad for road and traffic safety!
• For high pressure sodium lamp, a dedicated power supply to the lamp power supply to light, Its brightness can not be transient rapid change. At night, in order to save electricity general road lighting can only be taken every two bright a way to reduce power consumption, but the two bright one way will make the pavement shadow zone, rhythmically light phenomenon the eye, to a luminance of the light has a relatively stable adaptability, so the flickering light pattern will have a certain risk, but also can not meet the " CJJ_45-2006_ city road lighting design standards " road illumination environment than the requirement of SR.
• Short service life, high maintenance cost.
• Light distribution difference, water drop spot effect, make a lot of unnecessary light transmission to the far away from. The ideal spot effect should be for the rectangular beam, and illuminate the road on both sides of a certain range (i.e., the bat wing light distribution curve ). 
• Large power, high cost of laying lines. Because of large power consumption, therefore the power supply copper wire diameter is relatively thick, LED lamp can use relatively thin copper wire can satisfy the same need. F, other defects.