Learning Event 4:
DETERMINE THE INTENSITY OF ILLUMINATION
1. In photography, light is the most important ingredient. The intensity
of illumination on an object depends upon the strength of the light source
in candlepower and the distance from the light source to the object. Light
intensity diminishes inversely with the square of the distance from a light
source to an object.
2. In figure 1-11, a card is placed 1 foot, 2 feet, 3 feet, and 4 feet from
a light source. Assume the card, which is one foot from the light source,
is receiving 640 foot candles of illumination. If you double the distance
to two feet, the card receives 1/4 the illumination or 160 foot candles at
If you move the card to 3 feet, it receives 1/9 the amount of
light or 71 foot candles. If you move the card to four feet, it receives
1/16 as much light as it did at 1 foot.
How light loss intensity