Leaves on the upper part of the canopy tend to shade and reflect light away from the lower leaves. The amount of light incident on a leaf decreases as sunlight passes downward through the canopy. Within a building, the amount of light, whether natural or artificial, will be further affected by curtains and blinds, surface textures, and reflectance from wall coverings, furniture, and other furnishings.įurther, leaves on a single plant differ in the amount of light that they receive.
#Light intensity windows#
Likewise, many factors can affect indoor light.Īccording to Manaker (1981), the amount of natural light that may enter a building is affected by the location of windows or glass surfaces through which light enters, the presence of trees and shrubs, roof overhangs, window screens and awnings, and the tint and cleanliness of the glass.Ī gray glass allows 41% light transmission while clear glass allows 89%. This causes a slight variation in the amount of light and heat that the earth receives. 1978).ĭepending on the particular time of the year, the sun-to-earth distance varies it is closest in January (about 147 million km) and farthest in early July (about 151 million km Davis 1977). Light intensity is also affected by dust particles and atmospheric water vapor, slope of the land, and elevation (Edmond et al. Maximum intensity occurs at the equator, and gradually decreases with increasing distance from the equator to the south and north poles. It gradually increases from sunrise to the middle of the day and then gradually decreases toward sunset it is high during summer, moderate in spring and fall, and low during winter time. The intensity of light can change with the time of the day, season, geographic location, distance from the equator, and weather.
#Light intensity full#
Some terms that are used with reference to light intensity are open or full sun, partial sun or partial shade, and closed or dense shade.īased on adaptation, crops can be classified as sun plants and shade plants with various intergrades in between. High light intensity means it is brighter compared to low light intensity.
The following intensity values in footcandle are given for some light conditions (Janick 1972): starlight – 0.0001, moonlight – 0.02, indoors near window – 100, overcast weather – 1000, direct sunlight – 10,000. To convert the intensity of light from the sun, for instance, 800 μmol m -2s -1 to footcandle, 800 is multiplied by 5 which results to 4,000 fc.Īnother unit of measurement is the mol m -2d -1 which describes the total number of photons received by an area of 1 sq meter in 24 hours. It describes the number of photons of light within the photosynthetic waveband that an area of 1 sq meter receives per second. However, the units footcandle and lux are merely based on visual sensitivity and do not provide information on the energy or photon content of light.Īccording to Runkle (2006), the better unit of light intensity for studies involving plant responses is the μmol m -2s -1. Two adjacent plants may have differential light exposure
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