What is a low-pressure sodium (vapor) lamp?

Low-pressure sodium lamp is an electric light source that uses low-pressure sodium vapor to discharge, and its glass shell is coated with infrared reflection film, which is an electric light source with reduced light attenuation and the highest luminous efficiency. Low-pressure sodium lamp emits monochromatic yellow light, which is used in places where there is no requirement for light color, but its "fog permeability" is very excellent, especially suitable for highway, traffic road, municipal road, park and courtyard lighting, which can make people clearly see objects with small color difference. Low-pressure sodium lamp is also an efficient and energy-saving lamp to replace high-pressure mercury lamp.

The principle of low-pressure sodium lamp is: using low-pressure sodium vapor (working vapor pressure does not exceed a few pa) to generate visible light source. The low-pressure sodium lamp was invented in 1930. After continuous improvement, the luminous efficiency of low-pressure sodium lamp has reached 450lm/W, which is the highest among all kinds of electric light sources. Principle of low-pressure sodium lamp: it is an electric light source that emits light based on the principle of low-pressure sodium-rare gas discharge. Because sodium is solid at room temperature, it is not easy to start a gas discharge lamp using only sodium. When the glass tube of the lamp is filled with mixed gas of argon and neon, that is, Pan Ning gas, the lamp first shows the characteristic red light of neon when discharging, and generates heat to raise the temperature of the discharge tube, which leads to the evaporation of sodium. Because the ionization potential and excitation potential of sodium are lower than neon and argon, the discharge quickly turns into sodium vapor, which radiates visible light. The radiation of low-pressure sodium discharge is concentrated on two double D spectral lines of 589.0nm and 589.6nm, which is very close to the highest value of spectral optical curve (555nm), so its luminous efficiency is extremely high.