Question
Download Solution PDFWhich of the below emits nearly monochromatic light?
Answer (Detailed Solution Below)
Detailed Solution
Download Solution PDFSodium vapour lamp:
It is low intensity so that the length of the lamp should be more. In order to get the desired length, it is made of a U-shaped tube.
This long U-tube consists of a small amount of neon gas and metallic sodium.
At the time of start, the neon gas vaporizes and develops enough heat to vaporize metallic sodium in the U-shaped tube.
Initially, the sodium is in the form of a solid, deposited on the walls of the inner tube.
When enough voltage is impressed across the electrodes, the discharge starts in the inert gas; it operates as a low-pressure neon lamp with pink colour.
The temperature of the lamp increases gradually, and the metallic sodium vaporizes and then ionizes thereby producing monochromatic yellow.
Important:
Advantages:
- Good efficiency
- Colour rendering is better than that of high-pressure sodium street lights
- Some lamps last far longer than the 24000-hour mark, sometimes 40 years
Disadvantages:
- Like many lamps, it contains traces of mercury which must be disposed of properly
- Human skin looks green under the light, it is poor for colour film/photography
- The warm-up time required to start the lamp
Applications:
Large areas like parks, street lighting, high ceiling buildings, and gyms
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