Tech Note DWM-MA500-whitelight: white is white
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To introduce this topic do the following exercise:

Stare unfocused at the white screen (/worked examples/DWM-MA500-WE-redscreen.exe) for 60 seconds then view a piece of white paper lit by a 40-watt bulb, a candle, or the sun at sunrise/sunset.

Kelvin Scale

The Kelvin temperature scale (K) was developed by Lord Kelvin in the mid 1800s. The zero point of this scale is equivalent to -273.16 DegC on the Celsius scale. This zero point is considered the lowest possible temperature of anything in the universe. Therefore, the Kelvin scale is also known as the "absolute temperature scale". At the freezing point of water, the temperature of the Kelvin scale reads 273 K. At the boiling point of water, it reads 373 K. The light spectrum is scientifically described in terms of color temperature, and is measured in degrees Kelvin.

White hot

A material or an object (usually termed a "black body") heated in a vacuum will begin to glow and it will glow a different color depending how much it is heated. As the heat of the material increases, causing it to undergo color change, each different color of the spectrum is reached and the temperature of the material is measured in degrees Celsius (or centigrade). By adding 273 to the Celsius temperature, the scientist is able to express the color temperature in degrees Kelvin. As incrementally greater amounts of heat are applied to the material, thereby gradually increasing its temperature, its color changes from black to what we perceive as "warm" colors (the red and yellow the material emanates), then to what we commonly call "cooler" colors. Blue is actually hotter than red, although blue is generally described as a "cool" color. Thus, 10,000K light has a lot of blue in it while 2,000K light leans towards red and yellow.

Color Temperatures Of Light Sources

The list below shows the color temperatures in degrees Kelvin of various light sources.

• 18000 clear blue sky, deep shade
• 16000 average blue sky, medium shade
• 13000 blue sky,thin white clouds
• 9300 computer monitor (W3 standard)
• 9000 hazy sky, light shade
• 8000 cloudy sky, light shade
• 7000 overcast sky
• 7000 electronic flash
• 6000 blue flash bulb
• 5500 photographic daylight (standard)
• 5000 flourescent light
• 4400 sun low in the sky
• 4000 moonlight
• 3400 photoflood (standard)
• 3200 tungsten studio lamp (standard)
• 3000 flourescent light (warm white)
• 2800 household 100-watt tungsten lamp
• 2500 sunrise 2000 candle

Ref. http://photographytips.com/page.cfm/301

Standardising white

It is important to set a standard for white for web work:

• the designer wants the users to share a common visual experience
• the design team needs to produce consistent colours
• black is black, and white is white, is the base for setting colors, greys and gamma For Web design, white temperature should be set fairly high, 7500-9300K.

You will have to use you own judgement here because various monitors will give different results, just try to get the white as pure as possible, not too yellow, not too blue.

Print work is usually standardised at 5000K (Called D50) which is very yellow. ---Joe Gillespie

I understood the standard to be 9300K both for the sRGB color space and for the World Wide Web, but it's remarkably hard to find documentary evidence of this. One should be aware that many people working in CG and design will be viewing web pages on their Apple Mac with the white set to an incredibly (to us) warm 5000K. ---Steve Lowe

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AP, DWM, SL 2003/01/20 16:45