The amount and the intensity of the light that the plant receives dictates much of a plant’s life cycle. Even though a plant that originated in a jungle (where it thrives in the shade of trees) appears to be getting plenty of light, the intensity of the light indoors is going to be much lower than what it needs.
Insufficient light usually manifests itself with paler foliage, lanky growth, and general lack of luster. When this happens you must do whatever you can to increase the light intensity for that plant. This can usually be rectified by moving the plant closer to the window, or moving it to another room with different light exposure.
When you change the light drastically for a plant do it gradually to accustomize to the brighter light. Plants will sunburn if they are put into too bright of a light after their skins have become tender from lack of light.
Plants should never be placed between a curtain and the window if the nights are cold, even if they are sun lovers. It is better to have a sheer curtain which will admit the light, and have the plant in the heated area.
via How to Grow and Care for flowering and foliage house plants.
