A colour temperature meter is a device used to measure the colour temperature of a light source, expressed in degrees Kelvin (K). Photographers use this tool to ensure accurate colour reproduction by matching the light source to the film or digital sensor's colour balance. By measuring whether the light is warm, cool, or neutral, a colour temperature meter helps prevent unwanted colour casts and ensures consistent lighting across a shoot. It is an essential tool in studio photography, product photography, and any situation where precise colour control is required.