Perhaps this is fairly basic stuff to many of you but I will write it out anyway… Most people have a good idea about what the difference is between warm white and cool white light… and its effect on ambience and apparent brightness. a few points…

The concept of “pure” white light is a distraction! White lght is actually a mixture of every colour under the rainbow – literally!  Light consists then all the colours we see in the spectrum from red through to blue, and the character of that light will depend on what is in it… Heavy concept…

So lets keep it simple if there is more red light in the spectrum than blue light the white light will have a slight red or warm feel and vice versa, proportionally more blue, it will feel starker…

If an object has warm earthy tones ie a brown leather couch or red brick wall, it will look better if the colour balance is warm. Without the warm colours in the light the object will appear flat, dull, and lifeless!

So where does temperature come in to this… 

Metal objects if heated enough will glow. We talk about something being white hot! That object – say a tungsten filament in an “old fashioned” incandescent globe is actually very hot approx 2500o C (or 2800o Kelvin). We take this to be “warm white”. If that filament was heated further (without melting) the light emited would gradually shift toward the blue end of the spectrum… so that at 4000K it would appear as cool white, 5000K “natural” and 6000K ‘daylight”

Very likely the bit of metal would have melted long before reaching such temperatures so this is theoretical! The effective temperature to create this effect!