Colorado Ag. Science Curriculum Section: Plant and Soil Science Unit: 5 - Environmental Factors Lesson: 2 Light Affects of Plant Growth

OBJECTIVES TO BE COVERED 1)Determine how light can affect plant growth 2)Identify signs of light stress in plants

Radiant Energy Visible light is a small segment of all the radiant energy given off by the Sun. –Examples: x-rays, gamma rays, ultraviolet rays, microwaves, and radio waves Radiant energy is measured on the basis of the wavelengths and placed on an electromagnetic spectrum.

Three aspects of how light affects plant growth 1)Color 2)Duration 3)Intensity

Light Quality Light quality refers to the color or wavelength reaching the plant surface. Sunlight can be broken up by a prism into respective colors of red, orange, yellow, green, blue, indigo, and violet. (ROY G BIV)

ROY G BIV R - Red and blue light have the greatest effect on plant growth. O - Incandescent light is high in the red or orange range but generally produces too much heat to be a valuable light source. Y G - Green light is least effective to plants as most plants reflect green light and absorb very little. It is this reflected light that makes them appear green. B - Blue light is primarily responsible for vegetative growth or leaf growth. I V - Fluorescent "grow" lights have a mixture of red and blue colors that attempts to imitate sunlight as closely as possible.

LIGHT DURATION A plants response to light duration is called Photoperiodism. Plants are responsive to the length of exposure to light. –Short day plants Chrysanthemums, poinsettias, and cotton –Long day plants Radish and lettuce plants, carnation, and ryegrass –Day neutral plants Rose, potato, tomato, and cucumber

LIGHT INTENSITY Intensity of light depends largely on the angle of the Sun, clouds, and the dust in the atmosphere. It is greater in the summer months when the Sun is higher in the sky.

LIGHT STRESS IN PLANTS Plants will show symptoms of inadequate or too much light. Plants with inadequate light will often look tall and spindly or “leggy” and blanched in color. Plants with too much light will often look stunted in its growth.