How is color temperature of light sources measured?

The measurement of color temperature is based on the color that a light source emits; this is typically represented in degrees Kelvin (K). The concept stems from the way an ideal black body radiator emits light at different temperatures. As the temperature increases, the light shifts from reddish hues at lower temperatures to blueish hues at higher temperatures. Thus, observing and determining the color of the light emitted by a source allows for the assessment of its color temperature.

In the context of the other options, a color wheel helps visualize colors and provides information about color relationships but does not directly measure color temperature. A spectroscope could analyze the spectrum of a light source but is more complex than what is generally needed to determine color temperature. Assessing the brightness of the light does not directly relate to its color characteristics and therefore does not provide information about the color temperature.