UPSC Prelims 2006 Q148: Science & Technology – Physics
Which one of the following is printed on a commonly used fluorescent tube light?
- (a) 220 K
- (b) 273 K
- (c) 6500 K
- (d) 9000 K
Answer: (c) 6500 K
Explanation
Colour temperature printed on a fluorescent tube light
| Value | Meaning |
|---|---|
| 220 K | Far too cold for lighting |
| 273 K | Freezing point of water, not a lighting rating |
| 6500 K | Standard daylight colour temperature printed on tube lights |
| 9000 K | Too bluish, not the usual tube rating |
A commonly used fluorescent tube light carries the rating 6500 K, indicating the cool-daylight colour temperature of the light.
Answer: (c) 6500 K.
Why each option is right or wrong
- (a) Incorrect. 220 K is far below any lighting colour temperature (220 is the mains voltage figure).
- (b) Incorrect. 273 K is the freezing point of water on the Kelvin scale.
- (c) CORRECT. Fluorescent tube lights are commonly labelled 6500 K (daylight).
- (d) Incorrect. 9000 K is not the usual rating of a commonly used tube light.
Key point
Commonly used fluorescent tube lights are labelled with a colour temperature of 6500 K (daylight).
Remember
Tube lights are labelled 6500 K, the daylight colour temperature.
Common mistakes
- Choosing 220, the voltage in India, as a temperature.
- Confusing colour temperature with the actual operating temperature.
- Not knowing tube lights are rated cool daylight.
Exam tip
Warm white about 2700-3000 K; cool daylight tube about 6500 K.
Sources
- Bureau of Indian Standards — IS 2418: Tubular fluorescent lamps for general lighting service
- Encyclopaedia Britannica — fluorescent lamp