Correct Option (c):
The value 6500 K printed on a fluorescent tube light refers to its colour temperature. Colour temperature is a photometric measure that describes the spectral characteristics of light emitted by a source, indicating its perceived "warmth" or "coolness." A colour temperature of 6500 K corresponds to "daylight white" or "cool daylight," which produces a bluish-white light. This specific colour temperature is widely adopted for general lighting, particularly in commercial and office environments, due to its neutral and bright illumination qualities.
Incorrect Options:
Options (a) 220 K and (b) 273 K represent extremely low temperatures, equivalent to -53.15 °C and 0 °C respectively. These values are unrelated to the colour temperature or any operational characteristic of a fluorescent tube light.
Option (d) 9000 K indicates a very high colour temperature, signifying a light with a significantly bluer hue than 6500 K. While such high colour temperatures are utilized in specialized lighting applications, such as professional photography or specific industrial settings, they are not typically found on commonly used fluorescent tube lights intended for general illumination.