The Best Kelvin For Growing Plants – How Many Should a Bulb Have?

Sharing is caring!

Last Updated on January 31, 2023

You’ve probably heard of spectrum light and how it plays a key role in the stages of your plant growth. If you are a newbie or have little experience with grow light, and you are wondering what the best Kelvin for growing plants is that a bulb should have, you have come to the right place.

This article will enlighten you on how to go about selecting the accurate light spectrum, color temperature, and many more key points to consider when purchasing grow lights for your plants. So, read on to gain some knowledge.

Plants are generally required to grow under sunlight and for indoor gardens, we make use of grow light to accomplish the purpose of sunlight. Some grow lights such as fluorescent bulbs have various colors of light required for various stages of the plant life cycle.

Before we dive into what the best Kelvin for growing plants is in a light bulb, let’s have a brief introduction to various colors of light.

A Brief Introduction to Light Colors And Kelvins

One of a plant’s basic needs is light. This can be in the form of natural sunlight, artificial light provided by grow lights, or any other type of light that can mimic sunlight. It is essential to supply your indoor plants with the correct light spectrum at their various stages (such as the vegetative period) for optimal growth.

It may seem reasonable to think because the sun supplies white light in full-spectrum, and therefore our grow lights should do the same. This is not true. Sunlight produces different colors of light and the plant receives all these colors.

Therefore, grow light should have these various colors of light. Plants, however, perform well with red and blue light with a little bit of green and yellow. Because sunlight and other forms of light generally consist of various colors. A simple illustration of the light appearance is through growing light color temperature and it can be delivered or provided by light bulbs.

Durolux t5 Ho Grow Light

The measurement of bulb color temperature in a source of light is measured in Kelvin, usually abbreviated K, and has a scale of 1,000 to 10,000, with certain specialized lights having even higher values.

As an indoor gardener, you need to familiarize yourself with the various color temperatures of bulbs for your plant growth. From the Kelvin scale, the lower-end scale has the soft hues of the red spectrum or cool white. On the other hand of the Kelvin end scale, we have the blue light spectrum otherwise known as warm white.

The red spectrum of light is required for the flowering and fruiting period in a plant cycle. It is the blue spectrum of the opposite end Kelvin scale, which is the daylight hue that is required for the vegetative period.

What Kelvin Do Plants Generally Need to Thrive?

What light  Kelvin do plants need for optimal growth? The most important thing to remember is that plants typically absorb red and blue light for photosynthesis and that natural sunlight is in the range of 2,700 to 7,000 Kelvin.

Plants need different Kelvins to thrive, depending on the stage of growth that they are at. To promote fruiting and flowering, go for lights that are in the range of 3,500 – 4,500 Kelvin.

Keep in mind however that what is provided here is a wide range. Different plants have different specific Kelvin needs to thrive. So before you purchase indoor lights, it might be best to check with a grow light expert to help you gain more confidence in the grow light that you choose to purchase. 

There are LED lights that are available in the range of 4,100 and 10,000 Kelvin. There is a very low chance you would ever need these types of bulbs but it is good to know that they are available, if there is ever a small chance that you require them. Lights that provide light that is about 4,100 Kelvin are neutral looking and will promote the growth of the leaf and stem. This light would not beneficial for the vegetative or flowering stages of growth.

What Kelvin Should a Light Be For The Vegetative Period Of Plants?

Now let’s get to know how many Kelvin a bulb should have in the vegetative period. The vegetative stage of a plant is between seed germination and the flowering stage of plant development. During this period, the plant is busy carrying out photosynthesis and accumulating the resources that will be required for the flowering stage.

How much light in Vegetative Period

Plants undergo vegetative growth during daylight hours, so it is beneficial to give indoor plants light that mimics daylight so that they can successfully vegetate.

The best kelvin for vegetative growth is in the range of 5,000 to 7,500 Kelvin. They use blue light at the extreme end of the Kelvin scale, the daylight hue. It is the daylight hours plants go through during their vegetative period.

Grow Light Bulb

We can refer to grow light bulbs as multitasking light bulbs. They mimic the effect of sunlight function on the various stages of your plants’ cycle.

T5 and T8 LED tubes are the most conventional grow light bulbs used in most indoor gardens. The Kelvin range of these bulbs usually comes in about 6,500 Kelvin more or less. So this is the color daylight temperature required by plants, especially during their vegetative period.

There are other types of excellent grow lights also. Another light bulb-like LED light is obtainable in 4,100 and 10,000 Kelvin. Note that a bulb that supplies light of 4,100 Kelvin is known as neutral-looking light. They really don’t do much work with plants that are undergoing vegetative stages.

How Long Should Your Grow Lights Be On For?

All plants have different requirements for light color and light intensity. When it comes to the duration of exposure, most vegetables and flowering plants need between 12 to 16 hours of light per day, with flowering plants requiring more time. Indoor plants should be given a minimum of 8 hours a day. This is to try and simulate the natural daylight cycle that they would typically experience per day if they were planted outdoors.

Putting automated timers on your grow lights would help make this process easier, so you wouldn’t have to worry about turning the lights on or off.

Where to Put Grow Lights

What is the best place or spot to place your grow lights? Ideally, the closer the grow light is to the plant, the better because it will receive more light. A grow light or bulb should be placed within a couple of feet of the plants so that they receive enough light, but not too much that they can get burned. Directly above the plants is usually best. If a light is placed more to the side rather than directly on top, it can cause the plant/s to lean over to try and “reach” for the light,

For other types of plants, however, such as those grown on a trellis, the placement of the lights will be different depending on the direction you want them to grow.

Conclusion – The Best Kelvin For Growing Plants

You must get the color of light for every stage of your plants right to that they can reach their maximum growth potential. The journey of plant growth and maturity from their seedling to adult, flowering, and fruiting phases require different colors of the light spectrum.

We conclude that the Kelvin range that a grow light or bulb should have for plants in their vegetative period is from 5,000 to 7,500 Kelvin. This is the blue spectrum on the Kelvin scale and the daylight hue. Also, for the flowering and fruiting stage in a plant cycle, the red spectrum is required.

The different light spectra may be needed to fulfill different functions, but both provide essential support for healthy and strong growing plants. Provide your plants with light that mimics the sun’s natural light and you will have happy healthy plants.


Is 4000K good for veg?

4000K bulb is that better for plants. It's the most common type of light used in greenhouses.

How many Kelvin does a plant need?

I believe it's the same as in your home, or at least in mine. There are different theories of how much heat is needed to grow a plant. 

The "Kelvin" theory says that each individual plant needs a different amount of heat. It's been estimated that a plant needs between 4 and 20°C above its ideal growth temperature to grow normally. But this is only an estimate. That's because the plant will adjust its rate of growth to match the temperature. The "Thermal Time" theory says that plants need to absorb enough heat to bring them up to the right temperature, then stay there for the time it takes to complete one cycle of growth and then go back down again. So they need more than one degree of heat to do that. The "Time and Temperature" theory says that you don't need to give your plant any more than the time it takes to complete one cycle of growth and then go back down again. This means that the amount of heat is less than the time and temperature theory

What color temperature is best for vegetative growth?

The best color temperature range from 5000K to 7000K.

What is vegetative growth?

Plants grow in two ways: by means of a shoot and by means of a root. A plant's shoot, or stem, is the part of the plant that grows above ground. The shoot is used to produce leaves, flowers, fruits, and roots. A plant's root is the part of the plant that grows underground. The root is used to take up water, nutrients, and minerals from the soil. All plants grow by means of photosynthesis. Photosynthesis is the process by which plants use sunlight to make food. The process takes place in leaves, and it is carried out by chlorophyll molecules. During photosynthesis, carbon dioxide (CO2. from the air and water from the soil combine to form glucose, which is stored in the cells of the plant.

Plants use sunlight to make food out of carbon dioxide and water. Plants grow vegetatively to increase their size and to provide more food for themselves. Vegetative growth also allows plants to grow taller.

What stimulates vegetative growth?

As with other organisms, plants grow in response to a combination of internal and external factors. Internal factors include: temperature, moisture, light, nutrients, hormones, and growth regulators (e.g., phytohormones). External factors include: nutrients, light, water, soil pH, and microbes. The plant hormone auxin is responsible for initiating the vegetative phase of growth in many plants. Auxin also regulates other hormones involved in growth. Nutrients Plants need both carbon (C) and nitrogen (N) to grow. When soil is depleted of these nutrients, the plant will stop growing until more C and N are available. The root system absorbs C and N from the soil, so as long as the roots are healthy, the plant should be able to grow. Some plants have special mechanisms for extracting nutrients from the soil. For example, peas and lentils store nutrients in their seeds, which are then released to the soil when the seed germinates. The amount of C and N needed by a plant depends on the species and variety. In general, most plants require 1-2% N and 1-2% C. However, some plants such as tomatoes, peppers, and eggplants require more N than C. Light Light is necessary for photosynthesis. Plants use light energy to convert water and carbon dioxide into sugars.

Sharing is caring!