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comparison and candle light looks almost red. Likewise, blue sky without the sun is very
blue although when you're in the shade everything looks OK to you and I. If you make a
photo in the shade the picture comes out way too blue or cool looking.
This is because different kinds of light have different amounts of red, green and blue.
Incandescent lights and candles have a lot of extra red because they make light by heating
something hot enough to glow. Blue sky has a lot of blue because the sky appears to be lit
by light scattering from assorted dirt particles and the various gas molecules which make
up the atmosphere. This scattering effect, described by Rayleigh, varies as the fourth
power of the wavelength. Fluorescent and metal halide lights have a lot of extra green
because they make light by exciting ions of gasses made from dog poop which glow
greenish.
Low pressure sodium (deep orange) street lights are always going to look orange because
they are orange. They are monochromatic with only one wavelength at 589 nm. They have
no red, green or blue light to balance.
High pressure sodium lights (whiter orange) can sometimes be white balanced. Most
cameras lack the range to do this. If your camera can, you can get the scene to look as if it
is under white light and not the orange of the street lights!
DEFINITIONS
The silly phrase "White Balance" comes from professional video. Videographers make it
tough and use a special kind of oscilloscope called a waveform monitor to match or
"balance" the signals from the camera's red, green and blue channels to make whites look
neutral under these different kinds of light.
In digital photography (and amateur video) we have it much easier. You can just press a
button to make whites neutral, or let the camera do this automatically. It's also trivial to use
this adjustment instead to make whatever colors you prefer.
Digital and video cameras have this adjustment and film cameras don't for the same
reason dogs and cats lick themselves: because they can. Since digital and video cameras
are electronic it's simple to set colors by adjusting each one separately. Film can't do this,
since color film is processed all at once. This is why we need color balancing and
conversion filters with film cameras and don't with digital.
Forget about Kelvin temperatures unless you're an engineer. Kelvin degrees work
backwards from how we expect them to work in photography and common sense. Kelvin
degrees are the same as Celsius, except for being 273 degrees apart. (C = K - 273.) This
scientific classification refers to how hot something would have to be heated to glow the
same color. Imagine your electric heater or range. At lower temperatures it's more red and
gets oranger as it heats up. If it got to 3,200 degrees Kelvin (3,200K) you have the same
color as a typical light bulb (and the heating element would explode). If you heated
something even more to say 5,500 K it would be brighter and bluer and similar to daylight.
Heat the thing up further to say 8,000K and it might be as blue as shade. Yes, the hotter
Kelvin looks bluer or cooler, which is why you should ignore this unless you are a scientist.
© 2007 KenRockwell.com 46 converted by Sándor Nagy