As the main arc strikes and the gas heats up and increases in pressure the light shifts into the visible range and the high gas pressure causes.
Low pressure mercury vapour lamp circuit diagram.
Again transition of the electrons requires least amount of input energy from a colliding electron.
Amalgam lamps use a mercury amalgam mix to control mercury vapor pressure.
A sodium vapor lamp is a gas discharge lamp that uses sodium in an excited state to produce light at a characteristic wavelength near 589 nm.
Rather than a cold spot the lamp s amalgam spot on pellet regulates mercury vapor pressure during operation and yields up to three times the uvc output of a standard low pressure mercury lamp of the same length.
As pressure increases the chance of multiple collisions gets increased.
Low pressure and high pressure low pressure sodium lamps are highly efficient electrical light sources but their yellow light restricts applications to outdoor lighting such as street lamps where they are widely used.
Two varieties of such lamps exist.
When a mercury vapor lamp is first turned on it will produce a dark blue glow because only a small amount of the mercury is ionized and the gas pressure in the arc tube is very low so much of the light is produced in the ultraviolet mercury bands.
A fluorescent lamp is a low weight mercury vapour lamp that uses fluorescence to deliver visible light.
In case of fluorescent lamp the mercury vapour pressure is maintained at lower level such that 60 of the total input energy gets converted into 253 7 nm single line.