Sodium Lamps

Sodium Lamps

street lights

Low-Pressure Sodium Lamps:

The discharge tube is similar in size to the fluorescent tube but consists of a special laminated glass coated inside a sodium-resistant layer. The long U-shaped discharge tube is encased in an outer vacuum envelope to provide thermal stability. During priming, the lamps emit an intense red glow due to the neon gas they contain.

The characteristic radiation of low-pressure sodium vapor is a monochromatic yellow, a color close to the maximum sensitivity of the human eye. With nearly 200 lumens/watt, low-pressure sodium lamps are currently the lamps that have the highest luminous efficacy. However, they remain limited to applications where color discrimination is not important, such as national roads and subways, as well as residential streets.

In many cases, these lamps are replaced by high-pressure sodium lamps which, because they are small in size, make it possible to better control the distribution of light, especially for urban lighting where light pollution constitutes a growing concern.

High-pressure sodium lamps:

These lamps are similar to high-pressure mercury vapor lamps, but offer better luminous efficiency (greater than 100 lumens/watt) and excellent luminous flux retention. The reactive nature of sodium requires a translucent polycrystalline alumina discharge tube because glass or quartz are unsuitable. The outer glass bulb is under vacuum to prevent arc formation and oxidation. Sodium discharge does not generate ultraviolet radiation, so fluorescent coatings are not necessary. Some light bulbs are frosted or treated to diffuse the light source
When the sodium pressure increases, the radiation passes broadband around the yellow line to give a golden white appearance. However, as the pressure increases, the efficiency decreases. At present, there are three types of high-pressure sodium lamps


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