How to Determine Sunlight Levels for Houseplants

Potted aloe vera plant on windowsill
Jaan Sokk/Photodisc/Getty Images

Most plants come labeled with information about their sunlight preferences. If yours doesn't, you can easily look it up online or in a reference book. This is valuable information because too much or too little light can quickly stress a plant and stressed plants are prone to disease, pests, and premature death.

It's often easier to determine the amount of sun out of doors, rather than inside. Outdoors you can easily see where it is shady and where the sun is hitting directly and warming things up.

Light is more subtle indoors and it may take some experimentation to find just the right spot for your plant. Here is a simple breakdown to use when determining if a houseplant will be happy in your home and where to place it once you bring it home. However, other factors, mentioned below, as well as the temperament of the plant itself, will all make a difference in determining optimal lighting for your houseplant, so you will have to monitor your plants and use some judgment about what is best for it.

Determining Indoor Plant Lighting

  • Bright Light: Bright light means a sunny southern or western facing window with bright, direct light all day long. It should get a minimum of 5-6 hours of direct sunlight each day, preferably more. This can be hard to accomplish in winter but resist the temptation to move your plant closer to the window, to catch every fleeting ray of light. Most plants that need bright light will not be able to handle the cold draft that increases the closer you move it toward the window. You would be better off supplementing the light by putting a plant light bulb in a nearby lamp.
  • Indirect Light: Indirect light can be either an eastern facing, bright window or in the interior of a room that receives full light from a southern or western facing window. While the plant will not be getting a direct hit of sunlight, it will still need light for at least 5-6 hours per day.
  • Low Light: Many rooms qualify as low light, especially in winter. Rooms with north facing windows, rooms partially shaded by outdoor trees and even tables set too far in the interior of the room to receive much light from a window, would all qualify as low light situations. If it is not a spot where you can easily read a newspaper, it is probably low light.

    Other Factors That Can Affect How Much Light an Indoor Plant Needs

    When you are determining how much light your houseplant will need, you will also need to keep in mind the cultural conditions the plant will be growing in. Determining the right lighting level for houseplants is not an exact science, but keep these factors in mind, when finding a spot to place your plant.

    Temperature: Plants positioned near a source of heat, such as a heating vent or electronic device, may not be able to handle as much bright light as a similar plant in a cooler spot. If your plant often looks like it is wilting, even though you give it regular water, it is probably the heat source and not the light.

    Humidity: As with temperature, a low level or lack of humidity in the air can cause plants to wilt and stress. If that happens, you can usually leave the plant in its optimum light conditions, if you also mist the plant regularly or provide a supplemental source of humidity, such as a shallow tray of water.

    Duration of Sunlight: Most plants need a full day's worth of sunlight. That can be hard to come by, during the short days of winter. Luckily many plants go dormant during the winter and this includes most houseplants. However, you may still need to provide some supplemental lighting, especially if you can't provide a spot with ideal light conditions for your plant.

    Seasonal Changes: It's not just day length that varies as the seasons change. The angle of the sun is also different. When the days are long and the sun is high in the sky, your western facing window may get full sun for the entire day. Come winter, when the days shorten and the low sun only comes in at an angle, even a western facing window will not be enough light for a plant that craves full sun.

    Finding the perfect spot for your houseplants may take a few tries. The best gauge is to keep an eye on how your plant is doing. If it seems happy and healthy, let it be. If not, try another spot.