CCT or Correlated Color Temperature is used to determine the color of light sources that are close to white. They are measured in the unit, Kelvin (K), and light sources are available on the market between 1800K, all the way up to 6500K.
An 1800K source of light is very warm, or orange/amber. They are typically used in hospitality settings where a very dim and intimate feeling is wanted. On the other end of the spectrum, a 6500K source is very cool or blue. They are typically used in settings such as a hospital or school where visual acuity is important. In the middle, a 4000K source appears very white.
Incandescent sources are found in the warmer part of the spectrum and possess a slightly yellow hue. These typically fall around 2700K. Halogens are still considered warm but have a slightly less warm CCT closer to 3000K. These sources are the most commonly found in homes, retail, hospitality, and museum settings. Most consider the warmer ranges of lighting to be the most comforting and calming.
One unique aspect of incandescents and halogens is that as they are dimmed, their color temperature decreases, turning from yellow to amber to orange. Often, restaurants will dim their incandescent sources way down at night, leaving only a warm orange glow radiating from the filament. Non-incandescent sources typically will stay the same hue as they dim.
Fluorescent sources come in a wide variety of color temperatures. This is because without phosphors, fluorescents would only produce ultraviolet light which our eyes cannot detect. Different phosphors in different quantities produce different colors. Fluorescents have frequently been used in areas where lights are on consistently for a long period of time as they are more efficient than incandescents. Office building, schools, and hospitals frequently utilize fluorescents.
LEDs, too, are available in all color temperatures because they also utilize phosphors to alter their color. There are carbon filament replica lamps that are as low as 1800K, fluorescent replacements that are as cool as 6500K, and many sources at many K in between. LED are quickly replacing all types of lighting because they are extremely efficient, have a very long lifespan, and can produce a large about of light from a relatively small package. You can find LED lamps almost everywhere these days.