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SETTING UP LIGHT COLOUR PROPERLY

Those who work with 3D rendering software such as Cinema 4D, Maya 3D, Blender, 3D Studio Max, etc ... often has the need to illuminate the scenes and subjects with different light sources in a realistic way, for this reason it is useful to know what is the relationship between the color temperature of a given light source, expressed in Kelvin, and the corresponding values in RGB to be set in its own rendering software.

Kelvin is used for any light also in RL.

Stars  have colour temperatures, some are red giants other are neutron stars that emit very blue light, our sun has a whiteish/yellowihs kelvin colour temperature.

The very monitor  or HMD  you use needs to have a calibrated white point that  has to match 6500 kelvin with a 2.2 gamma to display proper sRGB information.

You commonly use directional lights in a scene to emulate the sun, and the sun  does `not always have the same temperature because of the atmosphere and its seasonal position, its angle at determined times of the day.

All these variables make it so that  proper sun set up needs to have a proper kelvin value applied to it.

The same is for spot lights,  or any light shapes and form or even IES, while u can adjust the intensity the temperature is a different value that is very important .

You can look up light manufacturers and see their lights specifications, and along with wattage they will also say the colour temperature  expressed in kelvin.

So u can precisely set a 25 watt lamp to have this colour that it is supposed to emit.

While this might seem an exaggeration to some, it is important to apply correct kelvin values, to achieve realism.

This does not mean that to achieve realism You cannot use green lights or purple, but that would be more of a ambiance aesthetic choice, or something very useful in a fantasy situation eg, a mars themed place, or some strange  world with a purple sky.

What you'll find below is a reference table of the correspondence of Kelvin of different light sources in the three main colors: red, green and blue.RGB values.

There is no mathematical formula to perform an "exact" conversion, the human eye has its adaptation to different light sources and performs a "white automatic" balance; actually an incandescent lamp emits a light orange light, the fluorescent light of a neon can have dominant ranging from blue to pink, the light of a cloudless day has a significant blue component - despite all this the human eye sees all these white lights.

To properly represent these and other light sources in a 3D rendering the project you need to properly set the light sources, as mentioned above each light source has its own particular color given by the emission spectra of the elements making up the same light source.


 

light source
Kelvin RGB  
match 1700 255,140,39  
candle 1900 255,149,44  
sunrise sunset 2000 255,160,75  
low pressure sodium lamp 2000 255,160,75  
high pressure sodium lamp 2300 255,180,112  
tungsten lamp 40W 2600 255,200,140  
tungsten lamp 60W 2700 255,205,150  
tungsten lamp 100W 2850 255,219,172  
fluorescent tube warm white (630,830,930) 3000 255,238,203  
halogen lamp 3200 255,248,224  
cool white fluorescent tube (640,840,940) 4000 255,249,230  
moonlight 4100 255,250,235  
white led 4500 255,250,240  
       
electronic flash 5500 255,253,250  
direct midday sun light 5600 255,255,255  
fluorescent tube daylight (665, 865, 965) 6500 249,251,255  
cloudy sky 7000 234,242,255  
fluorescent tube skywhite (880) 8000 213,230,255  
clear sky 20000 66,159,255

 

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