How Does Light Affect Plant Growth?

Ed Wike
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Why Do Plants Need Light?

Water and light are the two basic necessities for keeping houseplants alive. Most plants need sunlight and at least six hours of uninterrupted darkness each day, so they can be kept in a room where there isn’t any electric light.

When you plant a plant in the ground, it grows because it is getting nutrients from the soil. When you keep a plant in the house, you are replicating the conditions in nature, without all of the dirt and impediments. As a result, you need to focus on nutrition and sunlight when learning how to best care for houseplants.

The goal in keeping a plant that stands by itself is to force it to elongate, causing the stem to stretch and bend. The plant will only grow if it thinks it is fighting for its life. In nature, it would only grow with its hostile surroundings.

Plants need sunlight for photosynthesis, the process of converting light energy into chemical energy that is stored. Plants use chlorophyll (a green pigment) to metabolize sunlight. During the process of photosynthesis, plants take carbon dioxide from the air and turn it into oxygen. Plants also use this process to produce simple sugars, which they use for energy.

What Kind of Light Do Plants Need?

Outside in their natural habitat, plants are exposed to sunlight. This is where they get their most important source of light: photosynthesis. This means that on average, plants in their natural habitat receive about 6 hours of sun a day. Although most plants can also grow in lower light conditions, being able to receive enough light is an important factor for a plant’s growth.

The sun provides different kinds of light (UV light, infrared light, etc.), varying in intensity, that allow plants to master the chemical reactions that promote growth.

The colors of light plants receive all have different effects on plant growth. For instance, blue light helps spur the increase of chloroplasts. Sunlight contains more blue light than the light that is produced by artificial bulbs or lamps.

Green light also helps increase chloroplasts. Red light does not increase the number of chloroplasts, but it works as a trigger for plants to start photosynthesis and absorb all the wavelengths.

Most everything we have around us is designed to give off light that appeals to the human eye (the color changes from white light to the range of colors your eye sees). Everything from lamps and light bulbs to the screen on your phone. Plants, however, need light that appeals to photosynthesis (the perfect green).

Light Spectrum

Lenses, and Plant Growth.

Plants use light to grow. In fact, the scientific name for plant growth is photosynthesis, which uses light to convert carbon dioxide (CO2) and water (H20) into glucose (C6H12O6) and O2.

Different types of plants need different amounts of light, and they also need the light in the right wavelength for photosynthesis.

Also, light helps to inform a plant how to grow.

Light travels in waves, and each of the different wavelengths in the broad spectrum of light is called a color. Scientists are able to measure the amount of light that each color has.

These measurements are commonly called light intensity, and they are measured in watts per square meter (WS/m2).

Many types of plant growth are tied to a specific wavelength of light. Some plants that use long wavelengths (red, orange, and yellow) for photosynthesis need less intense light than those that use shorter wavelengths (blue and violet) for photosynthesis.

Plants, in turn, emit certain wavelengths of light as well. The energy created by photosynthesis is transformed. Plants use this energy for a variety of purposes, including growth and building new tissue.

Phytosynthetically Active Radiation

Plants have an internal clock that tells them when to initiate growth, flowering, and germination. They also need light to tell them when to do these things. Plants need light to live for the following reasons:

They make food from photosynthesis, in the presence of light.

Photoreceptors help to guide the plant to the light. (Essentially, they use the sun as a GPS or steersman).

Photosynthesis produces oxygen which is required by all other organisms on the planet.

By measuring the amount of one type of light that plants absorb, it’s possible to make some generalizations about the need for light and the way they use it based on the rate they grow.

Phyto means plant, and synthetically means producing, so phytosynthetically means plant producing. Plants create food by photosynthesis, and sunlight is needed to make this happen. Photosynthesis happens in the presence of light. When the plant receives light, it will have a positive change in the natural growth cycle of its chemical make-up and physical appearance. Phytosynthetic active radiation means the wavelengths of visible light that are necessary and beneficial to plants.

When it comes to indoor gardening, light is one of the most important factors because it affects a plant’s ability to grow. When you want to grow plants in indoor gardens, it is important to know that too much light can be just as harmful to the plants as too little light.

Sunlight is the natural source of light for plants. Plants that are grown outdoors, such as potted flowers, trees, grass, and vegetables, require a lot of sunlight. However, if you are growing indoor plants, such as orchids, cacti, spider plants, Boston ferns, and hanging plants, there are some light-related growing problems that you should watch out for.

The first problem is too much light. Providing too much light to plants, particularly when they are young, can actually harm them. To add to that, do not place your indoor plants near windows because they receive too much sunlight that can dry out the roots of the plant, causing brown spots and can even lead to diseases.


Let’s start with the basics. Light is one of the six essential elements of life. Light means photosynthesis. Photosynthesis is the process that green-leafed plants (chlorophyll-producing organisms) use to convert sunlight to fuel. The fuel is a combination of water and carbon dioxide.


One of the first things that you'll hear (and worry about) is how to get those "sunshine" plants to grow. When it comes to light duration, sunlight is considered natural, and during the daytime, these plants like to be outside in the sun.

Artificial light has a variety of technologies and options, and it is measured in lumens.

While artificial light can get quite expensive, most people use these for viewing and tend to overlook for plant growth.

Most artificial light does not have enough lumens to promote plant growth. It is more for providing a source for viewing during the evening hours. The "sunshine" plants need several hours of light a day, and they need full-spectrum light.

Farming plants will do well with artificial lights, and you may want to buy greenhouses that come with LED lights.

The good news is artificial light is much cheaper than natural light fixtures. But if you want to boost plant growth, you may find that they are not potent enough and need more light.


What is white light? The electromagnetic radiation visible to human eyes falls on the spectrum between 400 and 700 nanometers (nm). The color of the light is determined by its peak wavelength.

Light influences plant growth in intensity and duration. Light can be measured in both intensity and duration. Gardeners consider the following to determine the best light for growing plants:

“Low”, 5,000 lux or less, is enough to read under without eye strain. This amount of light will promote foliage growth but not fruits or flowers.

“Medium”, 5,000 to 10,000 lux, is enough light to grow plants without much eye strain.

“High”, 10,000 lux and more, is enough light for horticultural lighting.

High-intensity light, such as sunlight, transmits the most light energy. Plants close to the light source are overgrown while plants on the edges of the light source are starved for light.

Indoor Grow Lights vs. Sunlight: Which Wins?

Growth results are directly proportional to the quality and quantity of light.

So if you want your plants to survive in a place of cloudy skies and gray winter days, you must simulate the most balanced, natural lighting wherever you go.

Hoods that come over your indoor plants mimic the sun to make the most of the plants’ growth every single day of its life.

Some of the most popular home indoor grow lights:

LED Grow Lights- Many people see the price of LED units as a deterrent to purchasing them. However, what you really want to look at is the number of units, not the price. When there is only one LED, the price is cheaper. Having more LEDs, however, increases the output of the unit.

High Pressure Sodium- These are probably the most common HID systems. These are the most intense lights available. This type of light doesn’t penetrate deeply into the plant, but is more focused. Because of that, it’s important to keep the plants within one to two feet of the light itself. The brightness of these lights increases a good amount and their efficiency is more efficient than any other HID system.