How much light output is needed for providing extraordinary growth to my indoor plants? That’s a common question for many household gardeners when deciding the best LED grow light coverage for their plants.

For deciding the wattage per square foot for LED grow lights, you also need to consider the PPFD level and DLI level to get the proper measurement. Both of them provide a better understanding of how many watts are being used by the plants in actuality. The general rule of thumb states that you need around 30 watts of LED grow light energy per square foot of growing room to get optimal light for your plants.

In this article, we will discuss how many watts per square foot for LED grow lights. So let’s jump right into it!

Primary Factors for Setting Up Grow Lights

Determining the size, type, and number of LED grow lights you need might get complicated quickly. It depends on many factors like light intensity, grow space, watts per square foot, plant requirements, etc.

There are mainly three basic requirements that you need to look out for while setting up LED grow lights for your plants.

1. Light Requirement

Plants need the correct light output to provide healthy growth and higher yield. The requirement for light depends upon the light intensity that the plant needs. It could require a higher light intensity or maybe a lower intensity. Figuring this out is the first major necessity.

Plants that have higher light requirements will need more light because of flowering needs or bearing fruits. Some of the examples would be citrus, tomatoes, eggplants, etc. But some plants have low light requirements as they don’t need so much light output to grow. Most herbs and lettuce fall into these sorts of plants.

2. Lighting Type

There are so many factors to consider when setting up a new grow light for your plant. If you’re new to this and don’t want to waste time calculating watts per square area, the number of LED lights you’ll need, and how many plants to cover.

You could always go for the easy route and get one or two fluorescent lights to start. CMH and LED lights might work just fine because of their ease of use, low operation cost, and longer life spans.

3. Growing Area

Knowing the exact size of the growing area is vital for specific reasons. If you’re unsure about the size of the place where your plants will grow, measure it out. Calculate a rough estimate on how many plants you’re planning to grow and the approximate grow room you’re willing to spare.

After you’re done with the factors mentioned above, you’re ready to set up the perfect LED grow light setup for your plants.

Determining how many LED watts for grow room

The grow room is crucial in deciding the actual wattage you’re planning to install per square foot.

Start by measuring the width and depth by foot and then multiply them together to calculate the area. The best wattage for growing weed in a 1 square foot area is 32 watts of energy.

The following table will show the grow space size needed for different wattages in a grow room.

Calculating The Correct LED Wattage

LED wattage calculation is quite simple. But before understanding how many LED watts per plant, you need to understand some basic concepts about the math.

Why Wattage is not the Perfect Measuring Method

For establishing the exact amount of wattage you need for your LED grow lights, the first thing you need to do is to identify the exact grow space of the room.

The second thing you need is the photosynthetic photon flux density, also known as the PPFD level. You need to multiply the size of the grow room and multiply it with the PPFD level. The result should then be divided by the PPFD watts per LED grow light.

An important thing to remember is that wattage is not the only determinator of the area you need to cover for the plants. It won’t determine how much power you need or the effectiveness of the grow light.

Basically, LED wattage is a standard measurement method for identifying how many lights you need for a specific fixture size in your grow space. More accurate measurement for light intensity is calculated by daily light integral, or DLI and photosynthetic photon flux density, or PPFD. Both are a more precise measurement of the light output.

Different light products show the level of watts per square concerning the maximum light wattage instead of the actual wattage of the grow light.

For example, if some lights have 300 diodes installed, each emitting 3 watts of energy, the maximum wattage would be 300 ✕ 3 = 900 watts of power. But in reality, these lights might draw only around 500 actual wattage of power while in use.

PPF and DLI will Provide More Accurate Results

For different LED lighting systems, PPF and DLI are more accurate representations of the light spreads utilized by the LED grow lights.

PPFD measures the light amount that is emitted by a light setup on a per-second basis. On the other hand, DLI is a measurement for the total light intensities a plant might receive per day. It calculates the photon numbers emitted per square meter per day for a specific plant.

For example,

Two lights have two different DLI measurements, one is 2.5 μmol/j, and another is 2.0 μmol/j. The second one might have higher wattage than the first one. But it doesn’t mean that it will have the same power or even more.

If we calculate the PPFD for both of the lamps,

The first one will emit 2.5μmol/j ✕ 500 W = 1250 μmol/s

And the second one will emit 2.0 μmol/j ✕ 600W = 1140 μmol/s

And as we can see, although the second one has a higher wattage rating, it will provide 100 μmol/s less energy from the light source. The light system for both grow lights is not equipped with equally good lamps in terms of power draw.

So we can conclude that when a lamp manufacturer states a particular power draw for a light, something like 500W or 600W, it refers to light energy for the diode as wattage. But it does not define power draw or the actual light spread by the grow light.

Listed Wattage vs. the Actual Wattage

All the LED lamps on the market come with a specific wattage printed on them to specify their power. But to obtain the right LED lights for your plants, you need to understand the difference between running them in their maximum LED wattage vs. the actual wattage that you can expect them to run in.

The specification might say that they can run in 3W power. But if you try to run them at that level, their life span will be reduced severely, and they might burn out. So the rule of thumb is to run them at around 60% of their actual listed wattage for getting the best light coverage per square feet and their reliability.

The following is a chart for understanding the actual wattage for different densities of plants.

Looking at this chart, you might notice a pattern for the watts per square needed for each grow light. It goes by the Square foot rule of thumb and calculates the amount of wattage required for any given case.

Determining The Grow Light Coverage

The indoor plant growers have agreed upon a rule of thumb. They have concluded that the minimum watts per square foot are around 30 watts for providing the plants with the optimal light output. To get a good light spread for your plants, it means that you need approximately 30 watts of energy.

So from this calculation, we can come to the chart that will show the optimal range of light coverage by the right LED lamps.

 Determining the Plant Number Per Wattage

The number of plants you can grow under a specific area depends on the wattage output from the grow lights. The higher wattage means more plants can get the optimal light for growth.

The following table will show the number of plants you can expect to grow under specific wattage.

 Determining the Light Number Per Plant

The grow light number you can use per plant is also an important metric. For standard grow light wattage of around 30 watts, the required light number can be calculated from the plant here.

Here is a chart that will help you with that.

 

Determining Light Level in PAR

Photosynthetic active radiation or PAR accurately calculates how many watts per plant LED light is needed. It is a standardized measurement system that has been in use by indoor gardeners for a while.

PAR defines the light spectrum that plants need for maintaining the photosynthetic process. It measures the total energy discharged for a particular light source that the plant can use to sustain photosynthetic pathways and growth.

So you can probably tell that the higher amount of PAR output comes from your LED grow light, plants can use more light for the biochemical processes.

Knowing the optimal lumens per square foot grow room might be a little tricky. So here’s a chart for helping you with that.

As you can see, the optimal PAR output is utterly dependent on the growth stage of your plants. As the plant changes from seedling state to vegetative to flowering, the overall PAR requirement increases almost threefold. The growth rate can increase up to PAR levels of 1500 µmol/m²/sec with optimum temperature and optimum CO₂ levels.

The highest level of PAR output that a plant can achieve for a good amount of yield is 750 µmol/m²/sec. Increasing the PAR output beyond this level won’t affect the growth level much.

An important thing to consider about PAR is that the measurement of PAR equates to the same rate of photosynthesis regardless of the color of the light spectrum.

Selecting the PPFD Level

Photosynthetic photon flux density or PPFD measures the amount of light reaching the plant per second. This particular measurement is done using micromoles per square meter per second. PPFD is considered to be one of the most critical measurements for LED grow light systems.

Most plants need more or less PPFD to enhance their overall growth rate and determine what size LED grow light do I need.

Here is a simplified chart for that. Let’s take a look.

●      Budget red/blue light: 0.9 – 1.2 PPFD/ watt

●      High spectrum red/blue light: 1.3 – 1.5 PPFD/watt

●      Full spectrum LED light: 1.2-1.5 PPFD/watt

If you have a grow room with 2 square meters of area, the total PPFD needed would be 2 × 750 = 1500 μmol/s considering the desired PPFD level is 750 μmol/s.

So, the PPFD output should be divided by the per watt requirement given above. So for full-spectrum LED lights, the wattage would be 1500 / 1.5 = 1000 watts.

PPFD is a standard measurement for calculating the wattage needs for plants, but other factors also need to be considered.

Deciding Factors for Choosing the Appropriate Grow Light

To get the optimal light output, there are specific parameters that you need to keep in mind for getting the best light spread. Each parameter has particular requirements from others, and they determine how many plants you can set to get the perfect coverage.

Some of the Deciding Factors are described here in detail.

Light Options

Different types of light provide different amounts of watts per square foot, and they draw different amounts of wattage from the electric board. More light doesn’t necessarily mean more yield. Depending on the plant canopy, different plant types will produce different outcomes.

The following are all possible lighting options that provide you with all ranges of LED grow light coverage.

LED grow light

These lights are cost-friendly and provide you with around 38% savings compared to other light types. LED lighting is also delightful for plants. They can grow quite fast if supplied with the correct wattage.

LED lamp types perform significantly better than other grow lights. There are many forms of LED lighting available on the market.

Fluorescent grow light

There are mainly two types of fluorescent light available- T5 grow lights and compact fluorescent light. It is also known as the CFL. CFL provides less wattage per light but has a uniform light intensity.

HID grow light

High Intensity grow lights, also known as the HID lights, have three main types. One of them is metal halide (MH) light, another one is high-pressure sodium (HPS), and the final one is ceramic metal halide light (CMH).

Although they have poor light spread than LED grow light, they have their own perks depending on the plant types.

Light Color

Which light provides how much watts per square foot shouldn’t be the only matter of concern when thinking about grow lights. Full spectrum LED grow light will give much better results than blue LED light. Even using different colored lights with the same light output, the plant growth won’t be the same under them. If you’re not using the right LED lights with the proper color, using twice as much light might not be enough.

For example, it has been found that using box LED grow light with red color will show deformity and poor growth on the plant leaf. For getting the best result, 30 µmol/m²/s blue light is required with the red light.

Following are the two best color options for LED grow light that you might want to look at.

White-colored LEDs:

Getting white-colored light from generic budget light isn’t an option if you want good plant growth.

A common trick is to use a reliable and efficient driver with medium efficacy lights like HPS and MH lights. These lights are the closest to the natural sunlight that you can get without emitting too much light in the process.

Full-spectrum LEDs:

A common problem with white-colored LEDs, no matter how many high efficacy lamps they use, is that they contain too much useless light spectrums like yellow and green.

A solution to this problem is to use a combination of multi-colored LEDs to provide the appropriate light spectrum to the plants. Many full spectrum LED lamps are available on the market. Choose one depending on the plant requirement and budget.

The Efficiency Of The Grow Lights

Getting high efficacy lights and putting them into the grow space isn’t enough. No matter how high watts per square the lights emit, the main question is how much the plants can absorb it?

Depending upon a few things, the light intensity and efficiency might increase or decrease. Let’s take a look.

Height of the Light

You can put grow light at any height, depending on the grow space. With every inch of change, the efficiency of lights per square will increase or decrease.

Usually, you want to follow this guideline for adjusting the height of the grow light. Seedling > Vegetative > Flowering > Harvesting. Each of these stages has different lighting requirements, and you can easily change the light intensity by adjusting the height of the light.

Alignment of the plant and light

If you’re using CFL bulbs or something like that, there are a few common light intensity hotspots where the light intensity will be most. So you can get pretty good wattage per square foot without using a powerful LED grow light.

There are some drawbacks too. As the light power won’t be even in all areas, it’s best to maintain average wattage for the entire space.

Light loss

It’s a fact that no matter how strong LED grow lights that you use for your plants, there will be some photon losses traveling from the light source to the plants.

If you’re an intelligent indoor gardener, you’ll think about minimizing the losses and think how many watts you can salvage. Using light reflectors and light luminaires will help to minimize light losses.

Chip Size

For applying the optimal wattage per square foot, chip size for the grow lights is also an essential consideration. LED grow lights can come in various chip sizes. Chip sizes determine what is the optimal range for watts per square footage in a grow room. They can range from 0.25 watts to 10 watts.

There are larger chip sizes available in the market, offering a higher watt count per chip. But for many indoor gardeners, 3-watt chips are the preferable size. If you want to control how many watts per plant LED grow light, 3-watt chips are the easiest to use.

They can perfectly balance the line between heat dissipation and penetration of light into the plant canopy. As most plant canopies are 5-6 feet in width, a 3-watt chip is more than capable of penetrating them to provide enough light. Especially for controlling how many watts per weed plant, 3-watt chips are our recommendation.

You can also get away with using higher chip wattage. But the downside is the extra heat that can be generated from them. You need to be careful about the heat or find out a way to dissipate the heat efficiently to get the maximum efficiency.

Minimizing the Light Costing

Providing LED grow light to your plant grow space is not a cheap task by any means. Every square meter will cost you a whole lot if you’re not careful. It’s essential to cut down the cost so that every lamp requires fewer watts to get into the optimal zone.

There are mainly two ways that can come in handy for saving your precious bucks on light watts.

Using Light Reflectors

The primary cost-saving idea that will save you a whole lot of watts per bulb is using a reflector. Not utilizing a reflector means that you’re losing almost half as much light to complete waste.

Different light reflectors are available on the market, and each offers a slight benefit than the others, depending on the plant.

Hood

Hood reflectors are best for intensifying the light output by directing the light from the bulb to the plant canopy. This type of reflector is best for urban gardening because of its high canopy penetration and light output.

Umbrella

For covering a large area with many plants in the grow room, an umbrella reflector is what you’re looking for. This reflector won’t offer too much penetration for the canopies, but it will deliver the lights to a lot of plants.

The circular shape might obstruct the light delivery. But its form enables grow lights to operate in an open environment.

Wing

Wing reflectors are the most used and most known reflectors to indoor gardeners. It’s because of their focused, yet more expansive light spread to cover a large area with good lighting. Wing reflectors are also relatively cheap, considering the other reflectors on the market.

Air-cooled

Air-cooled reflectors have a unique trick up their sleeve – they can lower the overall heat generated by the lights for saving electricity. Air-cooled reflectors are effective at smaller grow areas. But they’re not effective in large rooms.

Using Luminaires

Reflectors help you save watts per square foot on your grow room. Another tool that is equally useful or even better at saving lights is luminaire. Using both of them together will deliver the highest amount of watts per square meter.

Luminaires range from a small amount of light saving 10-100 µmol/m²/s to high efficacy lamps emit saving 2000 µmol/m²/s.

There are mainly three types of luminaires available.

1. Tubes

These types of luminaires are perfect for small grow spaces where light intensity is low. Tube lights are appropriate if you have a small grow room focusing on tissue culture and vertical farming.

2. Bars

For bar LED grow lights, the light intensity can vary in a lot of cases. They are placed in high or medium indoor spaces, where they tend to cover a wide range of plants saving precious watts per square meter.

3. Boxes

If you’re looking for high-intensity lamps that can produce a whole of watts per square meter, box grow lights are what you’ve been looking for. They can cover a large grow room and are typically used for a more significant number of plants.

Frequently Asked Questions (FAQs)

How many LED watts for 2✕2 grow room?

The exact LED watts requirement for a 2×2 grow room is entirely arbitrary. The calculation varies depending on a lot of conditions. However, a general rule of thumb defines that 120 watts should be enough for such a small grow room.

How many LED watts for 2✕4 grow room?

Choosing the number of LED watts needed to light up a 2×4 grow area is completely arbitrary. The formula changes based on a wide range of factors. For a small grow room, 280 watts should be sufficient, according to a general consensus.

How many LED watts for 3✕3 grow room?

Ideally, one can’t choose the exact number of LED watts required to light a 3×3 grow area. The formula is subject to change depending on a variety of conditions. According to most experts, 300 watts should be adequate for a small grow area.

How many LED watts for 4✕4 grow room?

A 4×4 grow space requires a certain number of LED watts to be lit. Experts agree that 500 watts should be enough for such a space. However, the calculation is subject to modification.

How many LED watts for 4✕8 grow room?

To light a 4×8 grow room, a particular number of LED watts is required, but the exact formula is subject to modification. Experts think that 1500 watts should be plenty for a small grow room.

How many LED watts for 5✕8 grow room?

A certain number of LED watts is needed for all sizes of grow rooms. In the opinion of growers, an 1800-watt setup would suffice for a 5×8 grow room.

How many LED watts for 8✕8 grow room?

For an 8×8 grow room, calculating the LED wattage needed is relatively unambiguous. The formula is subject to several variables. Even though it’s a massive grow chamber, 3000 watts is a good starting point to test out the canopy.

How many LED watts for 10✕10 grow room?

Based on opinions from experts, 4000 watts should be more than enough to grow your desired canopy in a 10×10 grow room. But do keep in mind that the calculation may change based on some other arbitrary factors.

What is 300 watt LED grow light coverage?

Having a 300 watt LED is relatively minimal, and it means you have a small grow space. You can, at best, grow 6-7 plants under such illumination. But based on some other factors, the number may change.

What is 600 watt LED grow light coverage?

A 300-watt LED light fixture suggests you have a moderately sizeable growing area but a tiny budget. Under such lighting, you can grow a maximum of 10-11 plants. However, depending on a variety of variables, this figure may alter.

What is 1000 watt LED grow light coverage?

Installing a 1000-watt setup means ample grow space to grow about 15-16 plants in the area. You can try stepping it up a notch by growing multiple species of plants under one roof.

What is 1500 watt LED grow light coverage?

By a generalized calculation, a massive canopy of 20-25 plants should be able to thrive under the 1500-watt LED setup. Such a large-scale setup is only useful if you take up home gardening very seriously.

What is 2000 watt LED grow light coverage?

Talking about 2000 watts means you are now in the big leagues. You don’t have to worry about a home garden anymore. You can grow up to 30 plants in this setup without having a sweat.

What is 3000 watt LED grow light coverage?

If you plan to grow more than 35 pants, a 3000 watt LED grow light setup should suffice. But remember that such a  massive scale will require other amenities to support the ample growth of your plants.

What is 4000 watt LED Grow Light Coverage?

It’s pretty rare to see home garden enthusiasts take up growing more than 40 plants at once under a home setup. But, if you’re just curious, an extensive arrangement of 4000-watt LEDs can cover up to 50 plants in your grow area.

How many LED lights for 6 plants?

For a small setup of only 6 plants in your grow area, you can opt for 10 LED lights at best. Any more than that won’t do you any good, but rather cost you unnecessary money.

How many LED lights for 12 plants?

A moderately large grow area hosting 12 plants can be supported by a setup of 20 lights. You can choose to install these lights in an orderly fashion so that you can get the most output from all your plants.

How many LED lights for 20 plants?

If you have an ample grow area and can produce about 20 plants in your home garden, get at least 36 LED lights. That will ensure the most economic output from your plants and provide an excellent cost-benefit ratio.

How many plants can you grow under 100w LED grow light?

Although the number of plants that can be grown under a specific wattage of LEDs is quite arbitrary, you can make a quick estimate about it. In general, you can grow 1-3 plants under a 100-watt LED grow light.

How many plants can you grow under 300w LED grow light?

Having a 300-watt LED grow light in your home garden means you’re taking it a bit more seriously than just a hobby. You can test it out with up to 6-7 plants under that coverage.

How many plants can you grow under 600w LED grow light?

You can grow more than 10-11 plants under a 600-watt LED grow light setup. Rest assured that you can get ample output from all your plants as it’s close to an ideal home garden requirement.

How many plants can you grow under 1000w LED grow light?

When you’re curious to know about the growth output of a 1000-watt LED plant, it means that you’re taking it very seriously. By a rough estimate, about 15-16 plants can be adequately grown under such a lighting setup.

Final Words

Deciding upon the proper grow space, the wattage requirement, the actual wattage calculator for both PPFD and DLI – all these are quite lengthy and take time. But once you understand the core concept behind all, you can harvest and cultivate any type of herbs and shrubs inside your house and put them with appropriate lighting.

If you’re just starting, using the 30-watt per square rule of thumb might be the way to go. This should clear up all your queries about how many watts per square foot for LED grow lights. Happy gardening!