Ok, this is where it gets complicated. But, since you asked…
Technicians measure luminous colour, or light temperature, in units of Kelvin (K). Zero Kelvin is actually minus 273°C.
The higher the temperature of a thermal radiator is, the “colder” the light looks. Some bulb manufacturers vary in their measurements, but generally the following scales are correct:
Warm white 2700 K – 3300 K
Universal white: 3300 K – 5300 K
Daylight: Over 5300 K
LED and energy-saving bulbs are not thermal radiators, but their luminous colour is described by the Kelvin-value that they are closest to.
While traditional bulbs produce a warm, golden light, halogen bulbs can only produce a whiter, sharper “daylight”.