You’re thinking of buying or have an LED grow light, and you need to make sure it’s properly sized for your garden. You’ve come to the right place. We’re the No. 1 online retailer of LED grow lights in the U.S. and we partner with laboratories to independently test LEDs for efficiency, marketing accuracy and overall effectiveness. Let’s use that knowledge to help you succeed in your garden, and maybe you’ll even teach your friends a thing or two.
Let’s start with the most basic ways to calculate what size LED grow light you need and move to the more complicated—and more accurate—methods.
How many LED grow light watts are required per square foot of grow area?
Most people think they need a certain wattage for a grow area. While wattage can be a good approximator for LED coverage, it’s not extremely accurate because coverage is affected by other factors, including how efficient the LEDs are and their beam angle. That said, if you’re a hobbyist growing in a tent or other small space, you can safely use wattage to give you a general idea of the proper LED grow light coverage for your area.
Here’s our quick-and-dirty guide to determine how LED grow light wattage can be sized to the square feet in a grow room or grow tent:
- Vegetative growth: 20 watts per square foot.
- Flowering: 30 watts per square foot.
In the table below, you can go up or down (+/-) 10% from the wattage calculations seen here and still have an acceptably sized LED grow light. For example, if we look at the 4’ x 4’ row we can see 480 watts for flowering. Dropping down 10% would be 432 watts, while increasing 10% would be 528 watts. Anything in that range will work well, but remember: The lower the wattage in your garden, the lower your yield.
|Grow Room Size||Square Feet||Veg Wattage||Flower Wattage|
|1’ x 1’||1||20 watts||30 watts|
|2’ x 2’||4||80 watts||120 watts|
|3’ x 3’||9||180 watts||270 watts|
|2’ x 4’||8||160 watts||240 watts|
|4’ x 4’||16||320 watts||480 watts|
|5’ x 5’||25||500 watts||750 watts|
|6’ x 6’||36||720 watts||1,080 watts|
|4’ x 8’||32||640 watts||960 watts|
|8’ x 8’||64||1,280 watts||1,920 watts|
|10’ x 10’||100||2,000 watts||3,000 watts|
How many plants per LED grow light?
A question often posed by new growers—how many plants per LED grow light?—is not the right question. We’ll use an example to explain why. Let’s say you have a 4’ x 4’ grow room with a 480-watt LED grow light. You could grow anywhere between one and nine plants comfortably. Yes, some people like to grow just one or two monstrous plants per light, and that’s OK.
The better question to ask is whether the LED grow light you’re using is properly sized for the grow area, which we went over briefly in the table above. A common mistake by novice growers is fitting as many clones and vegetative plants in a grow area as possible. If you do that, they’re all growing over one another when it comes time to flower the plants. That can lead to lower yields. Plants need ample space to branch out and grow without running into a lot of other plants in the process.
For more guidance on how many plants you should grow within your given grow space under LEDs, see the reference table below.
|Grow Room Size||Square Feet||Recommended # of Plants in Veg||Recmommended # of Plants in Flower|
|1’ x 1’||1||Up to 2||1|
|2’ x 2’||4||Up to 4||Up to 2|
|3’ x 3’||9||Up to 9||Up to 5|
|2’ x 4’||8||Up to 8||Up to 5|
|4’ x 4’||16||Up to 16||Up to 9|
|5’ x 5’||25||Up to 25||Up to 12|
|6’ x 6’||36||Up to 36||Up to 20|
|4’ x 8’||32||Up to 32||Up to 18|
|8’ x 8’||64||Up to 64||Up to 36|
|10’ x 10’||100||Up to 100||Up to 48|
See Our LED Testing Results and Comparisons
We are having all of the bulbs that we sell tested ourselves and we are sharing all of the data with you! Check out some of the data that we have collected so far.
- HLG 350R vs Mars Hydro FC 3000 LED Grow Light Comparison
- Growers Choice TSL ROI-E420 vs Black Dog LED PhytoMAX-2 400W
- California Lightworks SolarSystem 550 vs Horticulture Lighting Group HLG 550 V2 B Spec
- California Lightworks SolarXtreme 500 vs. Phlizon CREE COB LED 400w
- Phantom PHOTOBIO MX 680W vs. Iluminar iL8x 670w
- HLG 600 R-Spec vs Spider Farmer SF7000 LED Comparison
How do you calculate how many LED lights do I need? ›
To determine the needed lumens, you will need to multiply your room square footage by your room foot-candle requirement. For example, a 100 square foot living room, which needs 10-20 foot-candles, will need 1,000-2,000 lumens. A 100 square foot dining room, which needs 30-40 foot-candles, will need 3,000-4,000 lumens.How do you calculate grow light? ›
Let's say you are growing in a 5' x 5' grow space. If your plants need 20-30 watts/square foot, and your canopy takes up 4' x 4' of that space, you will need 320-480 watts of grow lighting.How much LED light do you need to grow plants? ›
As a rule of thumb, aim for 20 to 40 watts per square foot.How many LED lights do I need for 4 plants? ›
|# of Plants||Square Feet||Wattage from Wall|
|1||4||120 to 140 watts|
|2||8||240 to 300 watts|
|4||16||500 to 650 watts|
|6||24||700 to 860 watts|
For the average space of 250 square feet, you'll need roughly 5,000 lumens as your primary light source (20 lumens x 250 square feet).How many watts is 3000 lumens? ›
|Lumens to Watts Conversion Chart|
|Lumens||Incandescent Watts||LED Watts|
Let's recap how to gauge how much light you need for a space. Multiply your room square footage by the footcandle requirement. For example, a 100-square foot living room, which needs 20 foot candles, will need 2,000 lumens. A 100-square foot dining room, which needs 40 foot-candles, will need 4,000 lumens.How many plants can I grow with a 1000w LED light? ›
This HPS and MH grow light kit will provide the necessary lumens to up to 6 plants in a 5x5 grow tent through the vegging and flowering stages. The power of this 1000w light is perfect for providing the coverage and depth to reach all of your plants.How far should 1000w led grow lights be from plants? ›
Lower wattage LEDs of around 200 watts should sit between 12-20 inches from the top of the plant. Higher wattage LEDs of 1000 watts and above should sit between 36-46 inches from the top of the plant.How many plants can I grow with a 300W LED light? ›
For example, one single 300W LED light fixture may be fine for one or maybe two plants, but it may not be enough to cover a bigger space with multiple plants. So make sure to reference any recommendations from the vendor and/or LED manufacturer on how much light you will need for your growing space.
Can too much LED light hurt plants? ›
Intense, direct light is great for some plants, but it will damage (or even kill others). The plant isn't able to convert all of the light into consumable energy, and the excess creates a heat issue over time. The plant might use available water to cool itself, which creates a moisture shortage as well.How far should a 300 watt LED light be from plants? ›
For established plants, they are already where they need to be in order to thrive. During the flowering stage LED Grow lights should be located between 16-36 inches from the plant canopy. Moving the grow light closer will increase the light intensity which can maximize photosynthesis.How many plants can you grow with 600w LED light? ›
2 month plants should give about 40g per plant, so with about 9 you'll be able to easily fill a square meter and get up to 400g per 600w light. 3 month autoflowering plants grow much bigger, however, so you should only plant 4 per 600w light.How long should you leave plants under LED lights? ›
To be effective, grow lights really need to be on for at least 8-10 hours a day. This can vary up to 16 hours, depending on the conditions. That's why LED grow lights are so popular – when they have to be left on all day, it's best to use an energy efficient type!How big of a grow light do I need for 4 plants? ›
A good rule-of-thumb for LED grow lights is 32 watts of actual wattage per square foot of growing space for flowering medical or other large flowering plants.How many lumens do I need for a 12x12 room? ›
As a handy rule of thumb, a sitting room or bedroom will generally require around 10-20 lumens per square foot, while a bathroom or kitchen will need a stronger level of lighting, at around 70-80 lumens per square foot. To work out the lumens you need, simply multiply the square footage of the room by this figure.HOW FAR CAN 1000 lumens go? ›
A 1000 lumen flashlight is quite bright and, depending on the lens or reflector design, powerful enough to reach a distance of 200 meters or more. This type of flashlight allows you to see objects from a far distance.How many lumens is a good grow light? ›
Light Brightness and Lumens
Vegetable seedlings and other “full sun” plants require about 2000 to 3000 lumens (at minimum) per square foot of growing space. So, if you're growing just a single standard tray of seedlings, using a grow light that emits 3000 lumens is sufficient.
A level between 4,000 and 8,000 lumens is ideal. This is a wide spread so you can choose the amount that is right for your bathroom size.Is 5000 lumens too bright? ›
A 5000-lumen LED bulb is a very bright light source, and if you are using it in a relatively small room, it can be very harsh. In this case, it is recommended that you use a 1000-lumen LED bulb. Under normal circumstances, garages, utility rooms, and warehouses are more suitable for 5000-lumen bulbs.
WHAT LED bulb equals 60 watts? ›
A 60-watt incandescent light bulb can be replaced with a 10-watt LED.What is the name of thumb rule for lighting calculation? ›
The watt per square meter method is fundamentally a rule of thumb method. This method of lighting calculation comes in handy when doing a quick calculation or double-check.What is the 80% rule in lighting? ›
This rule states that an OCPD can be loaded to only 80% of its rating for continuous loads. Remember that 80% is the inverse of 125% (0.80 = 1 ÷ 1.25) and, as such, the rules are indeed identical in their end requirement.What is the formula for lighting ratio? ›
Since the lighting ratio is the ratio of the light levels on the brightest lit to the least lit parts of the subject, and the brightest lit are lit by both key (K) and fill (F), therefore the lighting ratio is properly (K+F):F although for contrast ratios of 4:1 or more, then K:F is sufficiently accurate.WHAT LED is equivalent to 1000w? ›
As can be seen from the guide, 300 watt LED is the best replacement for your 1000 Watt Metal Halide.How much area will a 1000 watt grow light cover? ›
These lights range in power from 100 to 1000 watts. The 400 and 1000 watt lights are the most useful. A 1000 watt grow light can light up an area of about 7 feet square when the light is suspended 2 feet above the plants. A 400 watt light would work for an area of about 4 feet square.
|Grow Room Size||Square Feet||Recommended # of Plants in Veg|
|6' x 6'||36||Up to 36|
|4' x 8'||32||Up to 32|
|8' x 8'||64||Up to 64|
|10' x 10'||100||Up to 100|
You need to divide your wattage by 1,000 (1,000 kilowats in 1 watt). So, if we were to run a 1000 watt grow light 18 hours a day with the kWh rate we gave earlier, our formula would be: 1 x $0.1559 x 18 x 30 = $84.186/month. $120.00 on sale until 12/24/2022! $250.00 on sale until 12/24/2022!How do you know if your plant is getting too much light? ›
Telltale Signs of Too Much Light
The most apparent sign is leaf burning. This typically causes the yellowing of leaves at the top of the plant but the veins stay green, and the leaves take on a yellow or brown, burnt look.
Electrical Safety for the Indoor Growrooms
A 1000w HPS or Metal Halide light takes 9 amps at 120 volts so you can only run one on a wall outlet circuit. A standard dryer outlet is 220 volts and 30 amps so you can power up to six 1000 watt lights on that circuit.
How far should 100w LED grow lights be from plants? ›
|LED grow lights Wattage||Distance from Plants|
|250- 400watts||16 to 30 inches away from your plants|
|450- 550 watts||20 to 30 inches away from your plants|
|600- 800 watts||28 to 42 inches away from your plants|
|900- 100 watts||36 to 46 inches away from your plants|
According to our current data, the average wattage required per square foot is 32 watts (although this also depends on the plant, so we are taking averages here), so a 4×4 tent theoretically requires 512 watts for complete coverage. This number can float between 500 watts and 600 watts.How far should LED lights be from seedlings? ›
How Far Should LED Grow Lights Be From Seedlings? Seedlings are delicate and should be started at the maximum recommended distance away from the LED grow light. A safe distance for all of the G8LED grow lights is 12-36 inches above seedlings to start, depending on the size of the light.Can plants burn from LED grow lights? ›
While LED lights do produce some heat, they deal with that heat more effectively than other light types. Plants can grow much closer to LEDs than other lighting types because of this. Usually crops can grow right up to the light without burning.What light do plants grow worst in? ›
Green light is the least effective for plants because they are themselves green due to the pigment Chlorophyll. Different color light helps plants achieve different goals as well.Can plants live with just LED light? ›
Offering low energy usage, low heat, and color optimized for growth, LED lights are the most efficient, effective, and customer-friendly way to grow plants at home than growing with fluorescent lights or incandescent lights.Does more light equal more yield? ›
Light Intensity and Yields
The light intensity rule of thumb is that a 1% increase in light equals to a 1% percent increase in yield. In a study by Wageninen University, they discovered this to be true of all horticultural crops they evaluated including, fruiting (vine) crops and flowers.
But, there's a reason why some of the largest commercial grow operations have made the switch to LED. A 600w HPS light can produce up to 150 to 300 grams in optimal growing environments, which is 0.5 grams per watt or less. LEDs, however, can produce as high as 1 to 1.5 grams per watt.Do LED lights yield more than HPS? ›
LEDs have much higher efficacy than HPS lights. LEDs are much more efficient than HPS lamps, which allows them to use lesser watts to achieve the same or higher output. The VOLT Grow® 720W FL-1 light produces a higher light output than a standard 1000W HPS light while using 30% less power.Do plants flower faster under LED? ›
Faster flowering can result in significant savings and better profitability for plant breeders. Various conditions can affect the flowering speed, but the quality of the light spectrum is probably the most important.
Can I leave LED grow lights on all night? ›
A: In general, you should not leave grow lights on 24/7. Plants need a light-dark cycle to develop properly. It's believed that they truly do “rest” during periods of darkness, and probably use this time to move nutrients into their extremities while taking a break from growing.How close can Buds get to LED lights? ›
The LED grow lights should be between 12-24 inches from the top foliage of your marijuana canopy. Monitor the plants closely to make sure they have enough light and not too much, which can cause adverse effects such as bleaching, discoloration, stunted or irregular growth.How many LED grow lights do I need? ›
To give you an idea, leafy plants need around a PAR of 200, while fruit-bearing plants would thrive between 400 – 500, depending on the plant. Knowing how much PAR a grow light has will affect how a plant grows. If the PAR is too low, your plant will have a hard time growing and will likely have stunted growth.How many LED lights can I put on a 12V battery? ›
You have a 12 V supply and each LED might need up to 3.5 V. (12 V)/(3.5 V) = 3.4 LEDs max. Since you can only have whole LEDs, the answer is 3.How do you calculate the number of light fixtures? ›
Multiply width of room x length of room x 1.5 = amount of total minimum wattage needed (assuming an eight foot ceiling). Divide by 60 to get the number of 60-watt equivalent bulbs required. Then, add up the wattage in each bulb in each fixture to figure out how many light fixtures are needed.How do you calculate how many lights you can put on a circuit? ›
Number of Lights
To calculate the current draw for each fixture, divide its wattage by 110 volts. For example, a 100-watt fixture would draw 100 divided by 110, or approximately 0.9 ampere. For 100-watt fixtures, you can have a maximum of 12 divided by 0.9A, or 13 fixtures.
“A good rule of thumb is 100 lights for every foot-and-a-half of tree,” according to Lowe's. But Better Homes & Gardens recommends using three 100-light sets for every foot of a tree's height. And Real Simple suggests 100 lights for every foot.What happens if you put too many volts through an LED? ›
LED lights require a certain voltage, such as 24 or 12V. When they run at higher voltages, they become extremely hot. Extreme heat damages the LED lights or the soldering around them. Due to the heat damage LED lights start to dim, flicker, or may die entirely.How big of a battery do I need LED lights? ›
The most common LED strip and battery voltage combination is 12V DC. Unless you have a specific situation that requires something else, 12V should work just fine. If you want to use standard AA batteries, you can use a battery holder that creates a 12V voltage from 8x 1.5V AA batteries.
24V is better suited for LEDs.
It is through configuring the LEDs in a particular parallel vs series combination, that the voltage of an LED system can be made to match a particular power supply voltage. Typically, a 12V LED strip is configured with 3 LEDs in series per string.
How do you calculate light spacing? ›
A good general rule for placement is to divide the height of the ceiling by two. The result is the amount of space to leave between each light. For example, recessed lighting spacing for a room with an 8-foot-high ceiling would be 4 feet between each light. This will provide good spacing for general room lighting.How many LED can lights per circuit? ›
Each CFL or LED bulb typically gives the same amount of light as a 60-watt incandescent bulb while drawing 10 watts or less, which is equivalent to a current draw of 1/12 amp. Thus a 15-amp circuit can safely control 180 or more fixtures that use CFL or LED bulbs.How many LEDs can be on a 20-amp circuit? ›
Therefore, a twenty-amp circuit can handle up to 38 LEDs. However, if you are using a 15-amp circuit, then you can install up to 30 LEDs. It is important to remember that putting more than 12 lights on a 20-amp circuit can cause the circuit to overheat and burn out.What happens if you put too many lights on one circuit? ›
Exceeding the rated load for the circuit wiring will trip the breaker, closing down the entire circuit. Without a breaker, an overload would overheat the circuit wiring, which could melt the insulation and cause a fire.What is the 50/50 rule right to light? ›
A right to light is a legal right to a particular amount of light in a room or space. Using the 50:50 rule, a right to light injury is defined as loss of light when the light within a room is reduced to less than 50% of the original amount. Not everyone has a legal right to light, so it's best to check.