How Many Watts Per Square Foot for Lighting? | Best Conditions for Growth Explained!

by Morgan

June 10, 2022

How To Choose The Right Lighting For Your Marijuana Grow Room

A question of how many watts one needs to use for lighting per square foot comes up rather often when one is looking forward to providing the perfect light output for their indoor growing. However, there is no concrete response in regards to the correct led wattage. The number of watts required for LED grow light per square foot depends on several vital parameters.

In this post, we will discuss the elements that should play a role in determining the LED wattage of the grow lamp that will provide your grow spaces with sufficient light, and we will share those considerations with you.

Indoor purple light on a plant

How Do You Calculate Watts per Square Foot for Lighting?

The watts per square foot (or square meter) approach can help estimate the number of LED grow lights or, more accurately, the light wattage that LED grow lights should have for indoor cultivation. That way, you can get the best yields.

Because the amount of light produced by LED grow lights is correlated to how much power (watt) is consumed, it is possible to quickly and easily give a rough estimate of one's light requirements by preparing the light layout for a cultivation space through established watts per square foot guidelines.

Calculate Watts per Square Foot to Select the Best Led Light for Your Grow Room

It is not unusual for members of the growing group to buy grow lights based on the "watt per foot or square meter" idea. Assuming that you are comparing different lights, this can be a straightforward and helpful strategy. If the lamp manufacturer doesn't give PPFD maps, watts per square foot could be the best option for evaluating a lamp's capacity to light a grow room or s grow tent

Compare the lamps since some lamps do better than others (higher effectiveness, PPE or µmol/J) and utilize fewer watts to output the right lighting. The Photosynthetic Photon Efficacy (PPE) shows us how effectively a lamp transforms the energy it receives from electricity (measured in watts) into light (photons).

Plants grown under less than optimal settings may show pros, yet they may not reach their full potential. Even if it falls slightly short of the recommendation, lighting a space 3 feet by 3 feet with a bulb with 200 watts of power instead of 225 watts will work quite well. However, lowering the amount of light any further to 150 or 100 watts would substantially negatively affect the yield. Alternately, raising the watts might boost the yield.

Close up of a lightbulb

Think About How Far the Light Can Travel

When you have a general idea of how powerful LED grow lights need to be for a grow room, the next thing you need to think about is how well the light will disperse across the same area.

Some lamps come equipped with focusing lenses, which create a powerful light source directly below the light source but a weaker light source further away from the center. The light from a lamp should illuminate the grow space uniformly, with the PPFD coming in somewhere between 600 and 900 mol/m2/s but ideally not falling below 200 mol/m2/s. Light intensity lower than 200 PPFD does not stimulate photosynthesis.

Due to their extremely efficient driver and diodes, high effectiveness lamps require fewer watts to generate the same light as a standard lamp. Diode brands such as Samsung, Osram, and Cree, and some versions of Bridgelux diodes, can deliver more light levels than generic brand diodes. A highly efficient system consists of high-quality diodes and a dependable and effective driver, such as the ones manufactured by Mean Well or Inventronics.

LED bulbs vary depending on the manufacturer and other factors. 

Man changing a lightbulb

The outside of two very distinct LED lamps might make them appear to have the same appearance. But what matters is the overall build quality and the diodes, driver, and energy discharged.

How Many Watts Do I Need to Light up a Room?

The proper application of high-quality lighting is one of the more challenging aspects of making a room beautiful. The amount of watts per square foot for lighting significantly impacts how well you accomplish this task. Sadly, many rooms either have an excessive amount of lighting, which causes the full spectrum, which should be enticing to become too harsh and repelling, or insufficient lighting, which causes many of the room's most beautiful aspects to be hidden.

weed growing

In most cases, the amount of High-Intensity Discharge, or HID, the lighting required to illuminate one square foot of a room adequately, is at least 30 watts. High-intensity discharge led lights to need to be at least 50 watts per square foot to provide enough illumination. When using fluorescent lighting, there 150 watts are needed to illuminate one square foot at a minimum and 250 watts of fluorescent light to illuminate one square foot at an optimal level.

Having a Solid Understanding of Watts and the Other Units Used to Measure Light

Usually, how much led light is emitted is measured in lumens, not watts; the lumen rating of a bulb is a considerably more critical factor in determining how brightly you may light a grow space. The measurement of light output, known as a lumen, is consistent across all varieties of incandescent bulbs. However, the lumen efficiency and rating of any individual bulb might vary considerably. Experts refer to the amount of electrical power that a light bulb consumes to produce its maximum amount of luminosity to its lumen efficiency. LED light bulbs are the most lumen-efficient type of light bulb currently available.

These are some straightforward definitions that can assist you in understanding these different units for measuring light.


A light bulb's quantity of electricity needed to produce its maximum light intensity is measured in watts. It refers to the amount of power that a light bulb needs to give you maximum yield for the growth stage. Particularly among the incandescent bulbs, you might come across certain light bulbs having wattage ratings of either 60W or 100W. Electrical power equal to either 60 or 100 watts is required to achieve the lumen output specified for these bulbs. There is no correlation between the wattage of a light bulb and the high light it emits.


The lumen is the unit of measurement used to describe how bright a light bulb is. It's how much light a bulb can emit in a given time. It is possible for a fluorescent bulb, an incandescent bulb, and an LED bulb to all have the same lumen, which shows that they generate the same quantity of visible light rays with each passing second. That implies that they illuminate a grow space with the correct proportions of light rays by logical extension.

However, for different bulbs to produce the same amount of lumens, an increased amount of electrical power is required. For instance, to make 1500 lumens, an LED bulb will need far less electrical power, measured in Watts, than both an incandescent bulb and a fluorescent bulb.

Lumen Efficacy

This is the ratio of the number of lumens produced by a light bulb to the number of watts it uses. We can measure the lumen efficacy of a light bulb by determining how many lumens it produces for each watt of power. That allows you to reduce your energy consumption while maintaining the brightness of the grow space.

Blue lightbulb

Light bulbs with an energy star rating often have a high lumen efficiency and save a significant amount of power. For instance, most LED light bulbs have high lumen efficacy since some of them can produce 1500 lumens while only using 10 watts of power. On the other hand, an incandescent bulb with 100 watts will put off the same number of lumens, although consuming ten times more power.

How Many Led Grow Lights for a 10x10 Room?

When lighting a section of a room, it is vital to consider whether the room requires minimal or optimal lighting. Since this will affect how the light is distributed and the needed watts per square foot. Consider the ideal light bulb for the room. You can use LED bulbs with lower lumen outputs in rooms that require less intense illumination.

The minimum amount of lighting required is thirty watts per square foot in most cases. That shows that a 50 square feet space will need 1500 watts of power. In addition, it is essential to think about the type of light bulb that will provide the illumination because different kinds of lighting produce a variety of different lumens. The suggested amount of power for lighting a room is 50 watts per square foot.

To calculate the number of watts per square foot of lighting required for any room, multiply the room's total area in square feet by either 30 or 50 watts, based on if you need the space to have minimal or optimal lighting. That will give you the required amount of watts per square foot of lighting. Also, think about your ceiling height since this might affect the amount of light that enters the room.

Indoor plant growing purple light

How Many Lumens Do I Need per Square Foot?

To determine the total lumen output that is necessary for your application:

Find out how much space there is in the room. To get the total square footage of a room, multiply its dimensions in both the length and breadth directions. For example, a room that is 10 feet wide and 10 feet long is 100 square feet.

Determine the footcandle criteria for the application—they need lighting changes based on the room that is being illuminated. A bathroom or kitchen, for instance, will call for more footcandles compared to a living room or bedroom.

Calculate the required footcandles by multiplying the room's square footage. For instance, a living room that is 100 square feet requires 20 footcandles and 2,000 lumens. A dining area that is 100 square feet and requires 40 footcandles plus 4,000 lumens.

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About the author 


I discovered the benefits of Cannabis at a young age in 2002, with years of trial and error, my knowledge grew just like my plants. As my love for cannabis unfolded I began to teach and learn, trying to gain as much information and practical growing experience.

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