The Light That Binds: Lighting for Young Plants

By Eric Hopper
Published: February 22, 2017 | Last updated: May 26, 2021 07:56:54
Key Takeaways

Building a strong foundation for a plant’s healthy growing cycle is shaped during its cloning/seedling and early vegetative stage. The most important influence during this time is lighting. Eric Hopper offers his insight on the best type of lighting and duration during this very delicate time in a plant’s life.

Source: L-51/Shutterstock

The lighting system of an indoor garden is the main driving energy behind all plant growth. In other words, if a grower uses an inferior lighting system, he or she will have lower yields and a lower return on investment.


Of all the equipment used in an indoor garden, the lighting system is the equipment that should be given the most consideration. After all, the lighting system will directly influence the rate of growth, the health of the plants, and the crop’s final yield.

When an indoor horticulturist asks me about ways to improve yields or a garden’s efficiency, I always revert to the garden’s lighting system. Small changes to the lighting system can result in big changes in the garden.


First and foremost, a grower must understand the importance of lighting. Once that concept has been buried deep in the grower’s mind, he or she can assess, maintain, and upgrade the system to better suit the garden.

For example, most indoor gardens consist of multiple rooms for different stages of growth. It is common for indoor horticulturists to have a dedicated cloning/seedling room, a dedicated vegetative room, and a dedicated flowering/fruiting room. Each room will have very different lighting needs depending on the type of crop being grown and the grower’s overall goals.

Read also: The Best Light for the Job


Foundation of Growth

A plant’s entire growing cycle will be shaped during the cloning/seedling and early vegetative stages of growth. In other words, these stages are the foundation and will directly influence the rest of the plant’s life cycle. One way to build a strong foundation is to provide proper during these critical stages.

There are many horticultural lighting technologies available that can promote plant growth, but the key to finding the best lighting system is to look at both the effectiveness and efficiency. Put another way, there may be lighting technologies that are effective, but are so inefficient that they cut into a grower’s return on investment. On the other hand, there are lighting systems that are inexpensive, both to purchase and to operate, but lack the ability to promote healthy plant growth.


Read also: A Plants Life from Seed to Seed Producer

seeds germinating in rockwool

The Cloning/Seedling Stage

The cloning/seedling stage is one of the most important stages for an indoor horticulturist to master. If the grower wishes to have a perpetual garden, a high cloning success rate is imperative for success. Horticulturists who grow from seed will also need to have a high success rate to have a productive outcome.

Some seed varieties are very expensive, so low germination rates are simply not an option. Along with keeping the atmospheric conditions consistent (crucial for success in the cloning/seedling stage), choosing the proper horticultural lighting system is imperative. The proper lighting system in this stage will not only help increase success rates, but will also increase the rate at which the plants can be rotated into the subsequent stages.

Read also: Seed Germination: How to Give Your Seeds a Strong Start

High Intensity Discharge

High intensity discharge (HID) lighting systems (including metal halide and high-pressure sodium) were once the industry standard for all stages of growth, including the cloning/seedling stage. Although HID lights will work during this stage of growth, they have a few disadvantages that make them less than perfect. During the cloning/seedling stage, plants do not need the light to be as intense as in later stages of growth.

A lighting system that is too intense can cause damage or retard growth. HIDs emit light from a single point on the bulb which means plants closer to the bulb will receive much more light than plants farther away. In other words, HIDs are terrible at creating uniform light footprints for small plants.

Inconsistency during early stages of growth can cause a whole slew of problems later down the line. Another disadvantage of HID lighting for the cloning/seedling stage is the immense amount of heat emitted. If not addressed, this heat may be too much for sensitive seedlings or tender clones.

Although it can get the job done, HID lighting is probably not the best choice for the cloning/seedling stage. HID’s intensity and requirements for additional ventilation equate to inconsistency and inefficiency.

Read also: Understanding the Different Types of Grow Lights Available

Seedlings in pots under fluorescent lights

Fluorescents and Light Emitting Diodes

Most professional indoor gardeners prefer fluorescents or light emitting diodes (LEDs) for the cloning/seedling stage of growth. Both fluorescents and LEDs offer a lower heat signature than HID lighting and generally are available in lower wattages. This is extremely important because the amount of light energy required by the plants is calculated by the size of the garden space.

During the cloning/seedling stage the plants are much smaller, which means they will not need as much light energy. This, combined with the fact that they simply do not need as much light during this stage, means a low wattage system is more suitable. A common rule of thumb for light energy in an indoor garden is 40W per square foot.

For the cloning/seedling stage, this number can be cut in half, so 20W per square foot is adequate for starting seeds or rooting clones. LEDs and fluorescent systems can be purchased in a wide variety of wattages so finding one that fits the exact area of a cloning/seedling space is not difficult.

Light Duration for Clones/Seedlings

Although there is debate regarding the duration of the lights on cycle for the cloning/seedling stage, most professional growers rely on a 24-hour lights on cycle. One solid argument for the 24-hour lights on cycle is it makes it easier to keep the temperature and humidity consistent. If a grower decides to give the plants a dark period during this stage of growth, the plants should still receive at least 18 hours of light per 24-hour cycle. This will ensure they are conditioned for vegetative growth.

Read also: Back in Black: The Basics of Light Deprivation Cultivation

The Early Vegetative Stage

One crucial stage of plant development that is often overlooked by horticulturists is the early vegetative stage. The early vegetative stage refers to the stage of growth immediately following the root development of a clone or the period of growth right after the second pair of true leaves appear on a seedling.

The early vegetative stage is the stage where rapid root development occurs and is also when the plants should be introduced to more intense lighting. The most common lighting systems used by professional gardeners during the early vegetative stage are T5 fluorescents. However, LED, HIDs, and other horticultural lighting technologies can be used effectively during this stage as well.

It is a good idea to introduce the plants to a light intensity (per square foot) similar to what they will experience for the rest of the garden cycle. For many indoor horticulturists, this will be 40-50W per square foot of garden space. During this stage of growth, the lighting technology is not as important as the amount of light the plants are receiving. However, consistent light intensity can make a big difference during the early vegetative stage. This is probably the biggest reason T5 fluorescents are so popular for this stage of growth.

Due to their construction, T5 fluorescents can supply the necessary wattage per square foot in the most consistent manner. Plants placed directly under T5 fluorescent lighting fixtures will get even light distribution regardless of location. This equates to uniform growth. Uniform plant growth is crucial in the later stages of the plant’s life cycle because an even canopy allows for the most efficient use of artificial lighting.

Read also: T5 Grow Lights: What You Need to Know

Creating uniform vegetative growth with T5 fluorescents is almost effortless, but what about other light technologies? HIDs and some LEDs disperse light differently and, in the case of small plants, unevenly. The plants closer to the center of the bulb will receive much more light energy than plants farther away. This will cause the plants to grow at uneven rates. Some growers will remedy this by rotating the plants on a regular basis to ensure more even light distribution.

Light Duration for Early Vegetative Growth

Early vegetative growth will require an 18-24 hour light cycle. Again, the optimal photoperiod for this stage of growth is continuously up for debate. Many growers have success with a 24-hour light cycle and many growers have success with an 18-hour light cycle. My personal preference is an 18- hour light cycle. I believe that all biological creatures, including plants, benefit from rest. Providing my plants with a six-hour dark period each 24 hours is my way of giving them a break.

To have a smooth transition into the vegetative and flowering stages, a foundation must first be built during the cloning/seedling and early vegetative stages. The lighting system used for these initial stages of the plant’s life should be heavily considered. Not only will choosing the correct lighting system be better for the plants, it will also make things easier for the grower. Professional growers still prefer the T5 fluorescent technology when it comes to the early stages of growth.

Regardless of which lighting technology a gardener uses, it really comes down to light distribution and consistency. Plants provided with uniform light energy during the early stages of growth will continue to grow evenly throughout the later stages of growth. Maximizing the performance of an indoor garden is all about maximizing the performance of the garden’s lighting system.

It is also important to remember that uniform canopies equate to larger yields. In other words, when plants are grown at a consistent rate, it makes it much easier for the grower to maximize the efficiency of his or her grow room. One of the best ways to ensure the plants will grow consistently in the later stages of growth is to create a solid foundation from the very beginning.

Read next: How Spectral Light Influences Plant Growth


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Written by Eric Hopper | Writer, Consultant, Product Tester

Profile Picture of Eric Hopper

Eric Hopper’s past experiences within the indoor gardening industry include being a hydroponic retail store manager and owner. Currently, he works as a writer, consultant and product tester for various indoor horticulture companies. His inquisitive nature keeps him busy seeking new technologies and methods that could help maximize a garden’s performance.

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