Light Affecting Growth

• Some plants do not require high levels of light for growth, because they are adapted to low light conditions (such as jungle and forest plants).
• Plants left in the dark will grow taller than plants in lighted conditions  but they will also be yellower and more spindly.
• Increased height is often a response to low light levels – the plant is trying to grow over anything that may be blocking the light, and will grow towards any source of light.
• Etiolation is an extreme form of photosynthesis, and it occurs when you keep a plant in the dark too long.
• When a plant is blown down, like this teasel, its efforts to regrow will produce distorted stems or branches.
• Plants on a windowsill may grow only one one side, towards the light, unless turned frequently. (I must turn my pelargoniums again this afternoon).
• Seedlings need good, even light as a spindly plant many not recover. Beware sun through a window can burn seedlings.
• Too little light and leaves may brown and drop off.
• Blue daylight bulbs are the best if natural light is unavailable.

For more details read science for schools

Etiolation is a process in flowering plants grown in partial or complete absence of light. It is characterized by long, weak stems; smaller leaves and often pale yellow coloring. 

Blanching is the exclusion of light to prevent greening up of Celery Leeks and other plants