An electric light source that produces visible light by discharge using low pressure sodium vapor (working vapor pressure not exceeding a few kPa). The low pressure sodium lamp was invented in 1930. In 1932, the Dutch company Philips commercialized low-pressure sodium lamps for the first time. After continuous improvement, the luminous efficiency of the low-pressure sodium lamp has reached 200 lm / W, becoming the light source with the highest luminous efficiency among various electric light sources. Low-pressure sodium lamp principle: It is an electric light source that emits light based on the principle of low-pressure sodium--rare gas discharge. Since sodium is a solid at room temperature, a gas discharge lamp using sodium alone is not easily activated. When the glass tube of the lamp is filled with a argon-helium mixture gas, that is, Penning gas, the lamp first exhibits a characteristic red light of krypton, and heat is generated to increase the temperature of the discharge tube, causing the sodium to begin to evaporate; due to the ionization potential and excitation potential of sodium It is lower than helium and argon, and the discharge is quickly transferred to the sodium vapor to emit visible light. The low-pressure sodium discharge radiation is concentrated on two double-D lines of 589.0 nm and 589.6 nm, which are very close to the highest value of the spectral light curve (555 nm), so the luminous efficiency is extremely high.
Low-pressure sodium lamp structure: There are two kinds of straight tube shape and U shape. Straight tubular low pressure sodium lamps are similar to fluorescent lamps. It has a double-ended lead arc discharge tube filled with a mixture of sodium and argon-helium, each with an electrode at each end. The discharge tube is sealed in a vacuum outer sleeve, and a double-pin base is mounted on each end of the outer sleeve. The U-shaped low-pressure sodium lamp uses a thin and long discharge tube with a small diameter to bend it into a U shape to reduce the volume of the lamp and to heat the bent ends of the tubes to reduce heat loss. The bulb of the discharge tube is made of sodium-resistant glass that is resistant to sodium vapor attack. In order to reduce the heat loss caused by conduction and convection, the discharge tube is placed in a vacuum cylindrical outer bulb, and a film transparent to visible light and reflecting infrared rays is coated on the inner wall of the bulb to reduce the heat radiation loss of the discharge tube. Improve the luminous efficiency of low pressure sodium lamps. Such a transparent infrared reflecting film layer is mostly composed of an indium oxide film layer.
A bracket is also mounted in the outer bulb of the lamp to support the discharge tube. Specifications: Power has 18W, 26W, 35W, 36W, 55W, 66W, 90W, 135W and other specifications. The life of a low-pressure sodium lamp varies depending on the number of ignition points during use, typically 19,000 hours. The light decay is smaller than other light sources, and the end-of-life fashion can reach an initial luminous flux of 80-85%.
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