Light Effects

• Plant growth processes rely on the energy contained inside light waves to trigger essential metabolism activities required for healthy development. Plants use light to initiate photosynthesis processes and can actually bend, or lean towards light sources in an attempt to capture as much light as possible. The cyclic patterns of night and day also provide a way for plants to schedule rates of growth and flowering. According to the University of Illinois Extension-Resource Network, photoperiodism represents the metabolic activities that take place as plants respond to cyclic patterns of light exposure.
  
  

Photoperiodism

• Photoperiodism processes account for why some plants only produce flowers in the spring, while others don’t show signs of flowering until the warmer summer months, according to the Biology Reference. This phenomenon was first discovered by two plant physiologists named Wightman Garner and Henry Allard who conducted experiments in 1910 to examine how day length affected flowering growth. Day and night periods were both found to play essential roles in plant life cycle processes, as a plant’s life cycle doesn’t complete until existing seeds give way to flowers.
  
  

Phytochrome Receptors

• According to the Biology Reference, photoperiodism takes place in specialized pigment materials called phytochrome receptors. Phytochrome receptors act as light sensors that integrate with a plant’s biological clock and provide a means for a plant to adapt to its lighting conditions. These receptors also absorb available light energy and use it to activate the genes involved in seed development and flowering. In effect, phytochrome pigments can measure the time periods that elapse through successive days and nights.
  
  

Effects

• Phytochrome receptors respond most to the energy contained in red and far-infrared light waves. According to Biology Online, two types of receptors, called P(red) and P(far-red) intercept these waves and coordinate plant metabolism processes accordingly. P(red) receptors absorb red light waves during the day, while P(far-red) receptors absorb far-red waves during dark periods. As each plant type requires only a certain amount of light wave, too much of one or not enough of the other prevents flowering from taking place. Also significant is a plant’s need for uninterrupted dark periods, as any length of light exposure disrupts absorption processes in P(far-red) receptors.
  
  

Types

• Photoperiodism processes have varying effects on different types of plants. According to Biology Online, a plant’s particular light-dark requirements can determine whether it’s able to survive in one environment versus another. As a result, different plants typically fall under one of three basic categories--short day plants, long day plants and day neutral plants. Short-day plants require short periods of light and longer periods of uninterrupted dark in order to flower. Examples of short-day plants include goldenrods and chrysanthemums. Long-day plants include petunias, asters and beets and require summer conditions where long days and short nights prevail. Day neutral plants, such as roses, corn and dandelions will flower regardless of how much light or dark exposure they receive.