- Definition of Low Pressure Sodium Vapour Lamp: An LPSV lamp is defined as a gas discharge lamp that uses sodium to produce light, combining characteristics of HID and fluorescent lamps.
- Working Principle: The lamp works by creating an arc through a gas mixture, initially emitting pink light and eventually producing a bright orange light as sodium vaporizes.
- Construction: The lamp has a borosilicate glass outer envelope with an indium oxide coating and a U-shaped arc tube containing sodium and inert gases.
- Photometric Parameters: LPSV lamps have a luminous efficacy of 150-200 Lumens/Watt, a poor CRI, a CCT below 2000K, and take 5-10 minutes to reach full brightness.
- Applications: LPSV lamps are used in road and security lighting, especially effective in foggy conditions due to their monochromatic light.
A Low-Pressure Sodium Vapor lamp (LPSV lamp) is defined as a type of lamp that combines features of High-Intensity Discharge (HID) lamps and fluorescent lamps.
An LPSV lamp is defined as a gas discharge lamp that uses excited sodium to produce light.
The constructional features of the LPSV lamp are given below:
- The outer envelope is made from borosilicate glass. The inner surface of the outer glass case is coated with indium oxide. This heat-reflective coating of indium oxide allows visible light to pass but reflects infra-red radiation back inside the tube as a result of which both light output and temperature inside the tube increases.
- The arc tube of the LPSV lamp is made of glass and bent in the form of a U-shape in order to increase the length of the arc. The arc tube is supported at both ends. The arc tube contains a mixture of metallic sodium and inert gases argon and neon.
The operation of an LPSV lamp is similar to other gas discharge lamps. An arc passes through a tube with metallic vapor and a starting gas, typically a mix of argon and neon. The operation is explained step by step in details below:
- Electric power is given to the lamp and it is energized.
- The electrodes produce an arc and this arc strikes through the conductive gas and the lamp produces a reddish-pink light, characteristic of neon.
- Current flowing through the inert gas mixture of argon and neon generates heat.
- This heat vapourises the metallic sodium.
- With the passage of time, the quantity of sodium in the arc stream increases and this produces the characteristic monochromatic orange color at a wavelength of 489.6 nm.
LPSV lamps operate best at a pressure of about .005 torr and a temperature range of 250° to 270°.
Photometric Parameters
The luminous efficacy of the LPSV lamp is around 150-200 Lumens/Watt. Its CRI is very poor as it is monochromatic in nature. Its CCT is less than 2000K and the average life is around 18000 burning hours. LPSV lamps are not instant starting and take almost 5-10 minutes to come to full glow.
Applications of LPSV Lamps
LPSV lamps are economical to use in road lighting and security lighting where the color of the object is not important. They are most suitable to use during foggy weathers
