Question map
With reference to street-lighting, how do sodium lamps differ from LED lamps? 1. Sodium lamps produce light in 360 degrees but it is not so in the case of LED lamps. 2. As street-lights, sodium lamps have longer life span than LED lamps. 3. The spectrum of visible light from sodium lamps is almost monochromatic while LED lamps offer significant colour advantages in street-lighting. Select the correct answer using the code given below.
Explanation
The correct answer is Option 3 (1 and 3 only). This is based on the technical and physical properties of both lighting technologies.
- Statement 1 is correct: Sodium lamps are omnidirectional, emitting light in 360 degrees, which often requires reflectors to direct light downwards. Conversely, LEDs are directional light sources, emitting light in a specific direction (usually 180 degrees), reducing light pollution and wastage.
- Statement 2 is incorrect: LED lamps generally have a much longer lifespan (typically 50,000 to 100,000 hours) compared to High-Pressure Sodium (HPS) lamps, which usually last between 12,000 to 24,000 hours.
- Statement 3 is correct: Sodium lamps produce a monochromatic yellow-orange glow due to their specific gas discharge. LEDs offer a broad spectrum of light, providing better Color Rendering Index (CRI), which improves visibility and safety in street-lighting.
Therefore, since statements 1 and 3 are scientifically accurate while statement 2 is factually wrong, Option 3 is the right choice.
PROVENANCE & STUDY PATTERN
Guest previewThis question is less about textbook physics and more about 'Technological Rationale'. It tests why the Indian Government (via UJALA/SLNP) aggressively replaced Sodium lights with LEDs. If you only studied the definition of an LED, you failed. If you studied 'Why LED is better than Sodium' (the policy logic), this was a sitter.
This question can be broken into the following sub-statements. Tap a statement sentence to jump into its detailed analysis.
- Statement 1: Do sodium street-light lamps emit light in all directions (approximately 360 degrees)?
- Statement 2: Do LED street-light lamps emit light in all directions (approximately 360 degrees)?
- Statement 3: Do sodium street-light lamps have a longer operational lifespan than LED street-light lamps?
- Statement 4: Is the visible light spectrum emitted by sodium street-light lamps nearly monochromatic (dominated by narrow sodium emission lines)?
- Statement 5: Do LED street-light lamps offer significant colour advantages for street-lighting, such as substantially better colour rendering (higher CRI) than sodium street-light lamps?
- Explicitly states that most sources of visible light (except lasers) emit light in various directions.
- Notes that such multi-directional emission allows light to scatter into the atmosphere, relevant to outdoor lamps.
- Defines electric light sources as luminous objects that emit their own light, placing street lamps in the category covered by general emission rules.
- Helps connect the general principle about light-source behaviour to actual lamps used in lighting.
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This statement analysis shows book citations, web sources and indirect clues. The first statement (S1) is open for preview.
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This statement analysis shows book citations, web sources and indirect clues. The first statement (S1) is open for preview.
Login with Google to unlock all statements.
This statement analysis shows book citations, web sources and indirect clues. The first statement (S1) is open for preview.
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