Colour temperature

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!

Brightness…

The common assumption is that higher the colour temperture the “brighter” the light… This assumption is not all together correct.

Brightness is a function of intensity more than what it looks like. Intensity can be measured with a light meter much like a camera does to ensure correct exposure  – remember photographic film? too much exposure the film would “burn out” and there would be no image… reduce the intensity – “stop down” the lens… success!… And in low light we would need a flash because it wasnt bright enough!

Increasing colour temperature might appear to be brighter to us, but we are seeing another effect… starkness! less red in the light, more blue and what we see seems bright but it isnt. Warm tones will go flat… will appear to be bleached as we might expect with film technology but we are seeing a lack of colour – not too much light. 

So on to ambience… What makes us feel good! What effect is right for the situation. Cool white light then might be right for certain effects but not others… Office lighting for example, or where nuetral or bluish tones have been used in colour schem. Lets go back to that raw red brick feature wall in the living room… cool white light wont do much to bring out the warm tones in the brick, and likewwise with timbers – they will look (if you can pardon the term) crap!

Lastly in this discussion Colour Rendition! – how well is that object being lit up, or more accurately am i seeing the true colour. 

Artificially created light (electronicly created rather than from lots of heat) will not cover the entire spectrum evenly. There will be sections of the spectrum where the intensity will be less than other sectons, so if those sections correspond to the colour of the object you are observing you wont see it in its full glory! This is particularly noticable when viewing artwork. 

For LEDs and flourescents, colour rendition is an issue. Quality does matter, and seeking out lightsources with CRI of 85 or better will ensure a better result. There is a lot more to say on these subject… More later!