Green plants require light to survive. Although different plants require differing amounts of light--some requiring full sun and others being able to survive in subdued light--any green plant will, quite simply, die without light.
Basics of Photosynthesis
Photosynthesis is the process through which plants use light to produce sugars which are subsequently used to create growth energy for plants. Photosynthesis occurs using the substance that makes the green color in green plants: chlorophyll.
Effects on Plant Growth
Adequate light allows plants to grow at optimal rates. Too little light results in lower production of sugars and slower growth. Plants that grow best in lower levels of light can often be damaged by direct sunlight through drying of plant tissues and through leaf burn. Too much or too little light can have detrimental effects on plant growth, depending on the type of plant.
Reaction of Plants to Directional Light
Many plants grow leaves that slowly turn to seek light. You can see this with plants left in the same position in a window. After a time period that ranges from several weeks to a couple of months, you will see many of the leaves turn toward the window because it is a consistent source of brighter light than the interior room. Plants requiring bright light in nature use this to turn leaves toward the sun when growing in shadier locations.
Green plants can be left for short periods of time in inadequate light. However, after a period of time, this lack of light will begin to affect growth and can eventually result in the death of the plant. For most plants, several days to a week will not cause major problems. However, although some plants can survive longer times, more than a week of inadequate light may start to affect some plant varieties.
If you grow plants in a window, rotate the plant every week or two to allow equal access to light to all sides of the plant. When planting inside or outside, consider light requirements when selecting plants for a particular location.