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Which of the following lamps is NOT a discharge lamp?
Incandescent lamp
Neon lamp
Sodium vapour lamp
Mercury vapour Lamp
Incandescent lamp
An incandescent lamp is a thermal radiator that produces light through incandescence (heating a filament to high temperatures). In contrast, discharge lamps generate light by the passage of an electric current through a gas or metal vapor, which excites atoms to release photons.
IS 2418:1977 (Specifications for Tubular Fluorescent Lamps)
An incandescent lamp is a thermal radiator that produces light through incandescence (heating a filament to high temperatures). In contrast, discharge lamps generate light by the passage of an electric current through a gas or metal vapor, which excites atoms to release photons.
P=I2R тАФ Power dissipated in a filament
E=h╬╜=╬╗hcтАЛ тАФ Photon energy emission in discharge lamps
In an incandescent lamp, current passes through a tungsten filament, heating it to approximately 2500┬аK to 3000┬аK, causing it to emit visible light. Discharge lamps use an electrical discharge between electrodes within a gas-filled tube, where collisions between electrons and gas atoms lead to electronic excitation and subsequent emission of light at specific wavelengths determined by the gas used (e.g., Sodium or Mercury).
Incandescent lamps operate based on black-body radiation principle.
Discharge lamps require an auxiliary ballast to limit the current due to negative differential resistance.
Incandescent lamps have a low luminous efficacy compared to discharge lamps.
Discharge lamps produce light through gas ionization rather than thermal heating.
Incandescent lamps have excellent color rendering index (CRI) of 100.
Discharge lamps offer significantly higher luminous efficacy and longer operational life.
Incandescent lamps have high thermal losses and shorter filament life.
Discharge lamps often require warm-up time and ballast circuitry.
Incandescent: Residential lighting, heating lamps.
Discharge: Street lighting, industrial high-bay lighting, signage.
| Feature | Incandescent Lamp | Discharge Lamp |
|---|---|---|
Light Generation Mechanism | Thermal Radiation (Incandescence) | Gas Ionization (Electroluminescence) |
Neon, Sodium vapour, and Mercury vapour lamps all function by ionizing gas, categorizing them as discharge lamps.
The incandescent lamp is the only option here classified as a thermal radiator.
A is correct тАФ An incandescent lamp relies on heating a filament until it glows, whereas other listed options rely on gaseous electrical discharges.
Always remember that any lamp requiring a 'ballast' or 'choke' is almost certainly a discharge type lamp.
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