SODIUM VAPOUR LAMP | An Architect Explains
Like in a Metal Halide lamp, the working principle of a Sodium Vapour lamp is that of a gas-discharge tube, but in this case, the discharge takes place through a tube with a small quantity of sodium-neon-argon (SOX lamp) or mercury-sodium amalgam (SON lamp).
These lamps are very efficient and last very long. But, unfortunately, they have very limited colour rendering properties, as they produce monochromatic, deep yellow coloured light only. Of the two versions, the SOX is more efficient, but the SON lamp has found better acceptance as it has slightly better colour rendition properties.
To help you in deciding the suitability of using Sodium Vapour lamps in your home, as an Architect, I have listed their advantages, disadvantages and usage under the following headings:
What are the advantages of Sodium Vapour lamps?
Where are Sodium vapour lamps used?
What are the disadvantages of Sodium Vapour lamps?
What are the advantages of LEDs over Sodium Vapour lamps in street lighting?
WHAT ARE THE ADVANTAGES OF SODIUM VAPOUR LAMPS OVER OTHER LAMPS?
Efficiency: Sodium Vapour Lamps are very efficient, turning one watt of power into a whopping 200 lumens! Compare this with the 12 lumens per watt of an incandescent bulb, or the 60 lumens per watt of a CFL, or the 90 lumens per watt of FTL.
Life: They have avery long life of 20,000 hours, compared to the 1000 hours of an incandescent bulb.
Light Colour: The monochromatic deep yellow wavelength light produced by the sodium vapour lamp is the ‘photopic’ range- in which humans see best. Hence the vision even in foggy and dusty conditions is excellent in this light.
WHERE ARE SODIUM VAPOUR LAMPS USED?
- Road Lighting: Due to the long life, efficient energy usage and excellent vision, the sodium vapour lamps are the ideal choice for road lighting, where colour rendition is unimportant.
- Monument illumination: They are also suitable for monument illumination, particularly those made of stone masonry of orange hue.
WHAT ARE THE DISADVANTAGES OF SODIUM VAPOUR LAMPS?
Colour rendering: The colour rendition properties are not comparable to the other lamps- the white SON lamp has a Ra value of 80 while the SOX has a Ra of just 20 which is way below that of an Incandescent (Ra -100).
Start time: Like all electric discharge lamps, Sodium lamps take some time to become fully operational.
Disposal: The Sodium Vapour Lamps contain mercury like all discharge lamps and need to be disposed carefully.
Since these lamps produce monochromatic colour, they are unsuitable for indoor applications. However, they find continued patronage among environmentally sensitive users, due to their efficiency and long life.
WHAT ARE THE ADVANTAGES OF LED OVER SODIUM VAPOUR LAMPS IN STREET LIGHTS?
With advanced technology, new, hi-power LED street lighting is threatening to replace the existing Sodium Vapour lamps as it gives a nice white light and energy saving of over 50%. Read more here:
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