Light

Light is the main source of energy for almost all ecosystems, because producers use it for photosynthesis. The light intensity, wavelength and duration (day length) all affect organisms.Light intensity. The rate of photosynthesis increases with light intensity until another factor becomes limiting. Where light is low, such as on a woodland floor under a dense canopy or deep in water, fewer plants can grow, so primary productivity is lower.Adaptations to shade. Plants that grow in shade often have larger, thinner leaves and more chlorophyll in their chloroplasts, so they absorb as much of the available light as possible. Many woodland plants such as bluebells grow and flower in early spring, before the trees come into leaf, when light still reaches the ground.Wavelength and water. Water absorbs red light more than blue light. In deeper water mainly blue-green light penetrates, so seaweeds that live deeper, such as red algae, have extra pigments that absorb the wavelengths available. Below about 200 m in the ocean there is too little light for photosynthesis.Day length. The photoperiod acts as a signal. It triggers flowering in many plants, and breeding, migration and hibernation in animals, so that these happen at the right time of year.Effects on animals. Light affects animals indirectly, through their food supply, and directly: many animals, such as woodlice, move away from light, which keeps them in damp, dark microhabitats.