Light is essential to the first stage of photosynthesis. This stage is appropriately referred to as the light-dependent reaction. This is the point during which the plant's chloroplast traps the light energy. This energy is then converted into chemical energy which will be used in the second stage of photosynthesis. The energy that is provided by light will ultimately assist in the creation of oxygen and carbohydrates.
The light itself has several different wavelengths, each a different color. Red and blue are the wavelengths that are most useful in the photosynthesis process, although all wavelengths except one are used. Green is the only wavelength that is not used in photosynthesis. The green wavelengths are reflected, giving plants their green coloring.
While plants need light for photosynthesis, they also use light to determine their growth pattern. Phytochromes are special chemicals that are released in response to the amount and duration of light that is provided. Plants will bloom in response to the number of hours of light that they receive. Some plants will bloom only when there are less than 12 hours of light each day, while others require more light to flower. Another reaction that plants have toward light is called phototropism. Phototropism is the movement of plants in response to sunlight. Plants will grow in the direction of the available sunlight, even when this results in uneven or leaning shapes.