Choosing the Right Light for Vegetative Growth

By Eric Hopper
Published: July 8, 2017 | Last updated: May 4, 2021 09:24:03
Key Takeaways

The lighting for the vegetative stage is just as important as the lighting for the fruiting and flowering stage. Here is a closer look at some of these lighting technologies.

In any garden, the vegetative stage is the foundation for a successful fruiting or flowering stage. After all, it is during the vegetative stage that the majority of the root mass is created and the plant’s structure (the spacing between branches and overall stem strength) is established.


It is also during this stage that many growers use manipulation techniques to shape plants to increase yields. But aside from the various plant manipulation techniques used by growers, there is one other vital component that prepares a vegetative plant for a strong finish: the artificial light source.

A garden’s artificial light is the sole energy source for all plant growth. It should come as no surprise that indoor growers spend a lot of time and money perfecting their garden’s lighting.


The lighting for the vegetative stage is just as important as the lighting for the fruiting and flowering stage. There are a few different types of lights commonly used by growers for the vegetative stage of growth and each has its own advantages and disadvantages. Here is a closer look at some of these lighting technologies.

Read also: Finding the Sweet Spot for Artificial Lighting

High Intensity Discharge (HID)

High intensity discharge (HID) lighting has been, and remains, the most popular choice of lighting for indoor horticulture. HID lighting has been present in the indoor horticulture market since the beginning and for good reason. HID lights work really well for growing plants because they are intense enough to penetrate the plant canopy and grow tall, robust plants.


The downside to using HID lighting during vegetative growth is the light dispersion. Since all of the light energy is emitted from one single focal point, there is an inconsistency of light energy across the garden.

Although light reflectors help create a more uniform light pattern, there is still much more light energy available closer to the bulb than farther away. To combat this, many growers will either rotate the plants or use a light mover.


Gardeners looking to grow monster plants should definitely consider HID lighting for the vegetative stage. Other lighting technologies lack the punch to produce tight node spacing (shorter distances between branches) on taller plants. The HID lighting category includes metal halide (MH) and high pressure sodium (HPS) lights.

Metal Halide grow lightMetal halides are usually screwed into a reflector or hood to create even more light for the plants. - sezer66 / Shutterstock

Metal Halide (MH)

MH lighting is one of the most popular choices for vegetative growth among indoor gardeners. The high amount of blue light emitted by MH bulbs makes this particular type of lighting an attractive option.

Generally speaking, plants given adequate blue spectrum light during the vegetative stage are less likely to stretch and create elongated node spacing (increased spacing between branches). Most indoor gardeners are trying to keep their plants short and bushy. When used correctly, this is not a problem experienced with MH bulbs.

Growers using MH for the vegetative cycle will never fall short of high-quality choices in bulbs, either. Lighting manufacturers have created many different, vegetative-specific MH lamps designed to emit a spectrum catered to vegetative growth.

Read also: The Gas Lantern Routine and Other Alternative Light Cycles

HPS grow lightHigh pressure sodium bulbs emit light primarily from the yellow to red parts of the visible spectrum. - nikkytok / Shutterstock

High Pressure Sodium (HPS)

HPS lighting is generally associated with the fruiting or flowering stages due to its higher output of red-spectrum light. However, many growers successfully use HPS lighting for vegetative growth as well.

HPS is the most efficient form of HID lighting and some growers will argue HPS is a superior vegetative light because of its efficacy. HPS bulbs need replacement less often than their MH counterparts and produce more light output per watt or energy consumed.

Advancements in HID lighting technologies—more specifically, the design and construction of the lamps themselves—have created HPS bulbs with more full-spectrum outputs.

T5 Fluorescent grow bulbs

Unlike other grow lights, T5 fluorescent lamps do not consume a large amount of electricity.

T5 Fluorescents

One technology that revolutionized lighting for indoor vegetative growth is the T5 fluorescent. T5 fluorescent lights are high-output fluorescents and are capable of producing great vegetative growth.

Some old-school growers may remember using T12 or T8 fluorescents for growing plants. The T5 technology blows both T12 and T8 fluorescents out of the water and has made fluorescent lighting a staple for many indoor growers once again.

The biggest advantages of T5 fluorescents are their high output and their light dispersion. Horticultural T5 fluorescents are either 2- or 4-ft. long, and because the bulb spans the entire distance of the fixture, the light energy emitted is uniform. This means all plants grown under a T5 fixture receive the same amount of light energy. This leads to uniform growth and a uniform plant canopy, which equates to a higher return.

Read also: Photoperiod Effects on Hydroponic Crops

Another big advantage of T5 fluorescents is their heat dissipation. Fluorescents are cooler-running than typical HID lighting fixtures, meaning the lights can be placed closer to the plants.

The closer the light source is to the plant canopy, the more light energy can be used by the plants. This more efficient use of light energy creates plants with tighter node spacing. Short, bushy plants are the most sought after for indoor horticulture and will generally produce higher yields than tall, lanky plants.

Due to their high output, even light dispersion and low heat signature capabilities, T5 fluorescent fixtures have become one of the most popular lighting choices for vegetative growth.

Young plant under LED grow light.Unlike other types of grow lights, LEDs do not burn a filament, but instead pass light through semiconductors to create their spectrum. - Nikkytok / Dreamstime

Light-emitting Diodes (LED)

Some of the newest technologies growers have adapted for vegetative growth are light-emitting diodes (LEDs). LEDs provide many advantages for indoor gardens. They have an extremely low heat signature, which means plants can be placed close to the light source, and some LEDs also have a customized spectral output.

In other words, LED fixtures can be made to produce a particular spectrum suitable for various types of growth. For the purpose of vegetative growth, many LED manufacturers produce fixtures with a higher output of blue spectrum. LEDs, like T5 fluorescents, can produce even growth in terms of both node spacing and plant canopy uniformity.

Read also: How to Set Up Your LED Grow Light for Growing Cannabis

Another large advantage of LED lighting is longevity. LEDs will not need bulb replacement like HID or fluorescent lighting. They can be used for 10-15 years before requiring replacement.

The largest disadvantage of LEDs is their price. Although an increasing amount of LED manufacturers continues to bring the price down, LEDs are still more expensive than other commonly used lighting technologies.

When purchasing LED fixtures, a grower is making a long-term investment. LED fixtures will eventually pay for themselves with the savings accrued from not having to replace the bulbs and the reduced heat loads.

Induction grow lightInduction grow lights combine both induction and gas exchange. - Ivan Karpov / Shutterstock

Induction Lighting

Most recently, two types of induction lighting have entered the indoor gardening market: induction fluorescents and sulfur plasma. Both of these lighting technologies can be used for vegetative growth with good results.

Induction fluorescents have similar qualities to T5 fluorescents, but their spectral output will not degrade over time. In many ways, induction fluorescents are the perfect vegetative light: they produce uniform light energy over the span of the fixture, have a low heat signature and last for 15 years.

As with LEDs, the biggest disadvantage with induction lighting fixtures is their initial cost, but for committed growers, they are worth considering.

Read also: Recycling Heat Between Dual Flowering Rooms

Sulfur plasma lighting is the most recent horticultural lighting technology to emerge. Sulfur plasma lighting has an incredible spectral output—closer to that of the sun than any other lighting technology—making it an ideal candidate for both vegetative and flowering stages.

As this technology is developed more for horticultural purposes, it is plausible that sulfur plasma lighting will eventually become the standard light source for indoor horticulture. Like LEDs and induction fluorescents, sulfur plasma lights last for 10-15 years without significant depreciation of usable light energy.

The initial cost for sulfur plasmas is still high, but over a long period of time, the advantages of this technology can make the initial investment worthwhile.

Vegetative Lighting Techniques

Regardless of the type of lighting technology one chooses for vegetative growth, there are a few general rules of thumb that will help growers maximize their growroom’s light energy.

First of all, always keep the light source as close as possible to the plant canopy. For vegetative growth, increased light energy equates to tighter node spacing and more robust stalks, depending on the crop.

In some cases, especially when growing a wide variety of plants, a grower may need to use manipulation to keep a plant canopy uniform. Topping, pruning, super cropping, tying down and trellising are all methods growers can use to keep the plant canopy as uniform as possible.

During vegetative growth, the lights should be on 18-24 hours a day. Although many growers will insist a 24-hour light cycle will speed up growth, I have always preferred an 18-hour light cycle. I believe plants, like all biological creatures, benefit from a period of rest.

Read also: Transition to Bloom Phase: When & How to Switch

Finally, make sure to replace HID or fluorescent bulbs used for vegetative growth annually. Even though the bulbs appear bright to the human eye, a significant amount of the plant’s usable light energy degrades after a year of use. Annual bulb changes will keep a garden’s performance in high gear.

The vegetative stage of growth can be compared to a marathon runner’s training period. For this analogy, the flowering period is the marathon and the vegetative stage is the athlete’s training for that marathon. Without the proper training, no marathon runner can be expected to have favorable results.

The same holds true with an indoor garden. Without proper vegetative growth, a garden cannot perform to its true potential in the flowering stage. For a marathon runner, training builds strength and endurance and is the foundation for the runner’s success.

In an indoor garden, the vegetative cycle is the time when a plant’s strength and vitality are built. With the proper lighting in the vegetative cycle, a garden can be properly prepared for the final event: a bountiful fruiting or flowering stage.


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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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