User Manual

30 Chapter 2 How Digital Images Are Displayed
Sources of Light
Prior to the invention of electric lights, electromagnetic energy originated from only a
few sources. Even today, the sun is the primary source of light. Fire and candlelight
provided evening light for thousands of years, though considerably weaker than
modern electric lights. Newer sources of light include incandescent light bulbs,
fluorescent light tubes, cathode-ray tubes (CRTs), liquid crystal displays (LCDs), light-
emitting diodes (LEDs), and some phosphorescent materials. These light sources
directly influence the images you create as a photographer.
The Color Temperature of Light
Color temperature is a term used to describe the color of light. Every light source has a
color temperature. However, color temperature refers to the color value of the light
rather than its heat value. Light’s color temperature is measured in units called kelvin
(K). This temperature scale measures the relative intensity of red to blue light. Warmer
light—light that tends to cast an orangish-red tint across the image—has a lower
temperature. Neutral or balanced light occupies the midranges, and has no effect on
the image’s color values because of its white qualities. Cooler light—light that is blue in
appearance—has a higher temperature.
Light source Approximate color temperature
Candle 1930 K
Sunlight at dawn 2000 K
Tungsten lamp
(incandescent indoor lamp)
2400 K
Typical indoor fluorescent bulb 3000 K
Photographic lamp 3200 K
Photoflood lamp 3400 K
Clear flashbulb 3800 K
Sunlight at noon 5400–5500 K
Blue flashbulb 6000 K
Electronic flashbulb 6000 K
Average daylight 6500 K
Blue sky 12000–18000 K