Demystifying Number of Lumens a Plant Needs

Every plant requires an adequate supply of air, water, proper nutrients, and light. If these conditions are not met, the plant would grow weak and eventually die. Change of seasons affects plants’ health due to sudden changes in the hours of exposure to daylight and temperature.

Sunlight is a vital requirement for plant growth. Without adequate exposure to light, plants may develop complications. Many homeowners prefer using grow lights for both indoor and outdoor plants. The lights offer auxiliary light or can be the only source of light in indoor gardening. 

Number of Lumens a Plant Needs

Lumen in Plants

A light source should provide enough light energy to sparkle the photosynthesis process. Excess or inadequate amount of light emitted by the source will have adverse effects on the plants. Lumen is the amount of light emitted per second from a particular source of light. The number of lumens required by plants is dependent on several factors:

  • Plant growing area
  • Distance from the plants and their height
  • Current growth stage of the plants          

Indoor gardening demands that you know the lumens needed by your plants to decide the number of grow lights you should install. It gives the plants enough light energy and prevents potential damage. 

A dull bulb brings a lazy feeling and will easily lure you to sleep. It doesn’t produce enough lumens, thus tricking your body with a natural inclination to sleep. A bright bulb, on the other hand, makes you more relaxed, upbeat, and focused.

The same principle happens in plants. Fewer lumens will lure them into resting and won’t make enough carbohydrates through photosynthesis. On the other hand, enough lumens make the plant maximize productivity and have a healthy growth cycle.

Indoor plants are not directly exposed to all the lumens produced; thus, cases of wasted lumens are unavoidable. Some light sources tend to veer off from facing the plants directly.

The perfect position of light sources is essential in indoor garden planning. While determining the total number of lumens required, you must put into account wasted lumens. Potentially wasted lumens is also a factor to consider when buying a light source. Choose a light source that produces more lumens than your plants require. 

How Many Lumens Does a Plant Need?

Certain crops thrive efficiently in indoor conditions. Some of the plants you can plant indoors are cauliflower, potatoes, beets, carrots, garlic, lettuces, tomatoes, spinach, and broccoli. You should know the lumens needed by each plant for the right product at the end of the day.

To measure the total lumens needed, consider the lumens needed by the plants per square foot. Check out the figures below. They are not perfect but have proved useful to many homeowners. With the right application, you should at least get productivity that is above average. The figures consider the use of a compact fluorescent bulb. 

In every square foot, CFL, the compact fluorescent bulb produces at least 7,000 to 7,500 lumens.  Minimum light requirements on any plant should be 2000 lumens per square foot and approximately 5000 lumens per square foot on mid-range.

A plant carries out photosynthesis at the vegetative stage. At this stage, more energy is needed for flowering and reproduction processes. Once your plants are in the vegetative stage, you should have 2000-3000 lumens per square feet in minimum. The exact number should depend on the plant types. More lumen will be required for fruiting plants like tomatoes. 

Plants at the flowering stage require more lumens since it’s the stage where reproduction takes place. We recommend around 5000 to 10,000 lumens per square foot.

There are several factors to consider before settling on the number of lumens needed per square foot.

  • Number of plants
  • How far apart the plants are from each other
  • Growing area size and
  • Type of plant grown

Plants respond differently to light colors. Light spectrum, which is an easy way to see light colors as colors of a rainbow visually, has different effects on plants. The effects cannot be seen with bare eyes but have nothing to do with the lumens released by the light source.

A full light spectrum refers to all colors produced by natural light. Sunlight produces a full light spectrum no wonder outdoor plants don’t need extra lighting fixtures since nature is well balanced. 

Different plant species require a certain number of lights to thrive and become productive. When dealing with indoor plants, you provide the light required by the plant for a certain period. Full-spectrum growth lights are more suitable for aquarium plants, growing plants, and flowering plants. Certain plants need bright light for a short period. For these plants, a full spectrum is needed with maximum lumens. 

The Difference Between Watts and Lumens

It is easy to confuse between watts and lumen. One might tend to think a bright bulb has more watts, but that is not the case. Watt is a measure of energy consumption. It does not determine the amount of light a plant receives. Traditional bulbs consume more energy than modern LEDs; thus, they have more watts while LEDs have fewer watts. Lumen, however, is a measure of the bulbs’ brightness. It determines the amount of light a plant will receive. 

For clarity, a 6-watt LED bulb can produce the same lumens as a 50-watt HID bulb. To have an effective gardening business, change your focus from watts to lumens. We must understand the amount of light (lumen) a plant needs for growth and development. Botanists and plant specialists do this by examining the photosynthesis process since it’s the stage where light energy is transformed to plant energy through glucose and sugar. 

Most commonly, plant leaves handle photosynthesis efficiently in 3000-4000 lumens per square foot. A 1000-watt grow light has an output of around 100,000 lumens. Considering a plant needs 4000 lumens for optimal photosynthesis, this means a 1000-watt bulb will have optimal coverage of 25 square feet.

When purchasing grow lights, you should consider lumens. Bulb manufacturers and garden shops will woo you to believe a 1000-watt bulb can cover between 40-50 square feet. However, it’s worth noting that most consider actual light coverage but not based on plants’ photosynthetic processes. 

Further looking at the lumens required for photosynthesis, you will note that an ideal temperature is essential for optimal photosynthesis; thus, the distance between the bulb and plants matters. Optimal photosynthesis occurs in 68 degrees F to around 74 degrees F. Temperature above 80 degrees F slows down the photosynthesis process.

Measuring Lumen

Lumen measures the total amount of visible light by the human eye emitted by a light source. Lumens are quite complicated to measure. A high number of lumens indicate more intense light from the lighting source. A lumen is measured using a lux or simply a square meter. Using British measurements, one lumen per square foot is equivalent to a foot candle.

Footcandle is a common unit used in light measurement. The unit emanates from the origin of candles as people tried to measure the intensity of light produced by a candle since it was the only available light source. 

Measuring lumens might require additional laboratory assistance. There is, however, a relationship between watts and lumens, a difference that might help you understand the number of lighting fixtures for your indoor gardening area.

40 watts is equivalent to 450 lumens
60 watts is equivalent to 800 lumens
75 watts is equivalent to 1100 lumens
100 watts is equivalent to 1600 lumens

Lumen Measurement Through Color Temperature

Blue: blue color promotes bushy growth in plants. It also encourages germination and vegetation.

Red: red lighting promotes flowering, fruiting, and budding in plants. There are many colors involved to make the full spectrum, but red and blue are the main colors. 

For an accurate number of lumens needed by plants, it’s of the essence; we look at a color temperature spectrum known as the kelvin scale and color rendering index (CRI). Kelvin scale is an easy scale for accurate lumen measurement through color temperature. We will look into this scale without getting more technical factors like CRI, color rendering index, PAR, photosynthetically active radiation, and nanometers.

Kevin scale bulbs. These are effective in determining the number of lumens you plan required. 6500K is enough to grow vegetables, young plants that need more light energy to grow, and seedlings. 3000K is enough when used for budding and flowering plants. Indoor aquarium plants thrive best in 10,000K light. Higher Kelvin scale is much cooler, and lower kelvin is warmer.

Common Grow lights

There are different types of grow lights used in indoor gardening. 

Fluorescent: This lighting is most common in cold months where plants do not receive adequate lighting. They are also common for indoor gardening as the sole light source for plants. Fluorescent lighting encourages flowering and the growth of seedlings. It comes in various types, like compact fluorescent bulbs, T5 and T8 bulbs. 

LED grow lights: Light-emitting diodes are popular grow lights since they consume less electricity than fluorescent and HIDs. LEDs have a cheaper installation and purchase cost and can be used over the long term.

High-intensity discharge bulbs: these bulbs have the highest lumen for indoor gardening. They are available as metal-halide and high-pressure sodium. It’s an expensive setup but also the way to go for professional growers.

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