The terms "cool" and "hot" used to describe blue and red light respectively have different meanings depending on the context. In the context of color temperature, the terms "cool" and "warm" are used to describe the color appearance of light sources, particularly in relation to incandescent lighting.
Color temperature is a characteristic of light sources that relates to the color of light they emit. It is measured on the Kelvin (K) scale. Lower color temperatures, around 2000-3000K, are considered "warm" and have a reddish or yellowish appearance, similar to the warm glow of candlelight or incandescent bulbs. Higher color temperatures, around 5000-6500K and above, are considered "cool" and have a bluish appearance, resembling the light from a clear sky or a computer screen.
The terms "cool" and "warm" in this context are purely descriptive and have no direct connection to temperature in terms of heat. They are used to describe the visual perception of the light's color. So, a "cool" light source has a higher color temperature and a bluish appearance, while a "warm" light source has a lower color temperature and a reddish appearance.
On the other hand, when we refer to blue light as "cool" or red light as "hot" outside the context of color temperature, it may be due to the psychological associations we have with those colors. Blue is often associated with coolness, calmness, and tranquility, while red is associated with warmth, energy, and intensity. These associations are subjective and not directly related to the color temperature of light sources.
In summary, the terms "cool" and "warm" in the context of color temperature describe the visual appearance of light sources, while the terms "cool" and "hot" used to describe blue and red light have more to do with psychological associations and are not directly related to temperature.