UPSC Prelims 2020 Q39: Science & Technology – Computer & Information Technology
- (a) 1, 2 and 3 only
- (b) 1, 2 and 4 only
- (c) 1, 3 and 4 only
- (d) 2, 3 and 4 only
Answer: (c) 1, 3 and 4 only
Explanation
Visible Light Communication (VLC): Technology Facts
| Statement | Claim | Verdict | Detail |
|---|---|---|---|
| 1 | VLC uses wavelengths 375-780 nm (visible spectrum) | TRUE | This is the visible light range. Violet (~375nm) to Red (~780nm). |
| 2 | VLC is 'long-range' optical wireless | FALSE | VLC is SHORT to MEDIUM range (10-200 meters typically). 'Long-range' is incorrect - confuses with fiber optics or free-space optics. |
| 3 | VLC transmits faster than Bluetooth | TRUE | VLC: ~100 Mbps (theoretical up to 1-10 Gbps). Bluetooth 5.0: ~2 Mbps. VLC is much faster. |
| 4 | VLC has no EM interference | TRUE | VLC uses visible light (not radio spectrum), so avoids RF/EM interference from WiFi, cellular, etc. |
Statements 1, 3 and 4 are correct. Answer: (c) 1, 3 and 4 only.
Answer: (c) 1, 3 and 4 only.
Why each option is right or wrong
- (a) Incorrect. Statement 2 is wrong (short-range, not long-range).
- (b) Incorrect. Statements 3 and 4 are also correct.
- (c) CORRECT. Statements 1 (wavelengths 375-780nm), 3 (faster than Bluetooth), 4 (no EM interference) are correct. Statement 2 wrongly calls it 'long-range.'
- (d) Incorrect. Statement 2 is definitively wrong.
Key point
VLC technology: Uses visible light (375-780nm) for wireless data transmission. Short-range (~200m). Faster than RF (Bluetooth, WiFi). No radio frequency interference. Challenges: Line-of-sight only, blocked by obstacles.
Remember
VLC uses electromagnetic spectrum wavelengths 375-780 nanometers (Statement 1 correct), is NOT long-range but medium-range (Statement 2 wrong), CAN transmit faster than Bluetooth (Statement 3 correct), and HAS no electromagnetic interference because it avoids radio spectrum (Statement 4 correct).
Common mistakes
- Confusing VLC (short-range visible light) with FSO (Free-Space Optics, longer range infrared/laser).
- Assuming wireless = RF. VLC avoids RF spectrum entirely, which is both advantage (no interference) and limitation (line-of-sight).
- Missing VLC applications: LED communication, underwater communication, indoor localization.
Exam tip
VLC advantages: No RF interference, faster data rates, visible light spectrum unlicensed, secure (blocked by opaque objects). Disadvantages: Line-of-sight required, range limited, blocked by obstacles/shadows.
Sources
- IEEE 802.15.7 - VLC Standard
- Daphne Okeya et al. - Visible Light Communications: Technology and Applications