Introduction

“In problem-based learning, the starting point for learning should be a problem, a query or a puzzle that the learner wishes to solve”

Boud. D, 1995, p.13. Enhancing Learning through Self Assessment

Types of problems that are solved by measuring light intensity

  • In photography or film production, creative manipulation of light can create stunning images from a low cost consumer camcorder, while poor lighting will cripple the most expensive, state-of-the-art broadcast camera.

  • Light intensity is an important management factor for breeder type poultry. There is evidence suggesting a minimum threshold intensity is needed to obtain optimal reproduction performance.

  • The amount of light received by a plant is an important factor, because plants' growth may suffer if they do not receive sufficient light. They may lose their characteristic shape and grow thin, leggy stems. New leaves may also be smaller and turn yellow. Some plants may lose their color or turn dark green. Plants exposed to excessive light, on the other hand, may not flower properly or may turn pale green. Different species of plants require different amounts of light.

Light intensity decreases dramatically with distance from the light source. An object located 15 cm from two 40-watt fluorescent lamps receive about 9300 lux, but only 5400 lux if they are 30 cm from the lamps.

The human eye is a very poor "instrument" for measuring light intensity, because the pupil adjusts constantly in response to the amount of light it receives. To accurately measure the light intensity in a given spot, it is best to use a light meter.

Light intensity may be measured in lux (metric system) or foot-candles (Imperial system). Note that 1 foot-candle = 10.76 lux

To provide some points of reference:

  • Full sunlight 11000 lux

  • Morning sunlight 6000 lux

  • A bright office has about 400 lux

  • Moonlight represents about 1 lux

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