All living things need food and water. For plants, light is food. They use it in a vital process known as photosynthesis, in which the energy of light is captured by chloroplasts, sparking several metabolic responses-- one of these being producing sugars (food) for plants. Sugars fuel plant growth, so the more light a plant is exposed to, the more energy it will make and the faster it will grow.
Know these pairs:
These properties of light are necessary in knowing how and why a plant will behave in your home.
Quality
Quality is based on the color and type of light. Light is energy that comes in varying wavelengths, each with a corresponding color. Colors we can see with our own eyes might not be beneficial for plants, since they 'see' light differently than we do. Plants look green because they reflect green light, so green light is useless to plants. Rather, plants need light they can absorb and make use of like yellow, orange, red, blue and violet, as well as invisible light like UV light from the sun and some infrared.
Quantity
Quantity of light is based on the intensity or the brightness of light that hits the leaves. The more light photons that hit the leaf = the more energy captured and faster growth. Begonias or Oxalis, for example, rely on strong light to maintain their fast-paced growth. Any kind of plant that makes flowers or fruits relies on strong light also. These plants are working with fundamental ingredients like water, CO2, sugars and nutrients that are chemically constructed into complex molecules, like flower pigments, but only when the right light intensity conditions are satisfied. Some plants have self-regulating mechanisms and will even refuse to flower or will attempt to but fall short midway through the process if there isn't adequate intense light.
In and Out
Outdoors, even in the shade, light is bouncing from all angles-- from 360 degrees around and from the 180 degree arc above in the sky. When a plant is indoors, light usually only comes from one source, like your sunny window, massively decreasing the angles light is bouncing off from, and the amount of light and vital photons a plant requires. When we bring a plant indoors, we actually invoke something called exponential reduction in photon exposure. The poetic quote above helps us remember this fact a little more easily.
Light Bright
You may have heard the terms "bright light" and "low light" plants, but what does that actually mean?
"Bright light" or "full sun" means there is no barrier (drapes or blinds, a tall tree or building that creates shade) between the plant and the source of light (a sunny window). This is where your plant will receive the most bright or direct light while inside. Ficus, succulents and Monstera are sun worshiping plants and should be placed right in or no more than 2-3 feet from a window. Generally speaking, you would want to put them in the brightest spot in the room.
"Medium light" or "filtered sunlight" is light that's been diffused (sheer drapes) between the plant and the source of light (a sunny window). Some refer to it as "dappled sunlight". Anything partially blocking the path between your plant and the source of light creates this medium light. Ferns and aroid plants (ZZ and Philodendron) have evolved to survive on the forest floor, so they are used to being shaded from the sun. They have not evolved to manage the strong rays of direct sunlight so they prefer medium light conditions.
"Low light" means no direct sunlight will reach your plant. It is most likely a few feet away from your source of light (sunny window) or any area where it can see outside but can not see the sky. Low light means less energy and also less food. Some plants can survive in low light environments however they will not thrive.
Remember that the sun changes places in the sky depending on time of day and season, impacting how much light your plant will get. Observe how the light changes throughout the year and adjust your plants placement appropriately.
