Best Light for Growing Plants Indoors
Best Light for Growing Plants Indoors | lintangsore.net
When starting growing plants indoors, one of the most important factors is light. Sure, you'll want to choose a good growstarting mix and establish a good watering routine, but proper lighting is crucial for healthy, stocky seedlings. The good news is that artificial lights, when used correctly, can give seedlings all the light they need to thrive.
Seedlings require lots of bright light, and when they don't receive enough of it they get tall and leggy. In most cases, even the sunniest windowsill will not provide the intensity of light they need. The best solution is to grow your seedlings under fluorescent lights.
Growing plants under lights, lets you control light intensity in two ways: the wattage of the bulb and how close the bulb is to the plant's foliage. Fluorescent bulbs are ideal for seedstarting because they give off very little heat. This means you can provide high light intensity by positioning the bulbs just 2-3″ above the foliage. Regular incandescent bulbs are not used for growing seedlings because they give off too much heat and can burn tender foliage.
As your seedlings grow, the fluorescent light fixture should be raised about once a week to maintain a 3-4″ distance between bulb and foliage. A light stand with one or more adjustable fixtures makes this task easy.
***
Horticultural lighting systems allow you to extend the growing season by providing your plants with an indoor equivalent to sunlight. This is a great advantage for those of you who appreciate having a year-round supply of fresh flowers, veggies and herbs. Artificial lighting is also a great way to jump-start spring by starting your seedlings months ahead of the last frost. There are three main types of horticultural lighting systems.
HID (High Intensity Discharge) Plant Grow Lights
HID lighting is the most efficient way to convert electricity into light that is available to the consumer. There are two types of HID grow lights used for horticultural lighting:
MH Plant Grow Light - ACFMetal Halide - MH
Metal halide bulbs produce an abundance of light in the blue spectrum. This color of light promotes plant growth and is excellent for green leafy growth and keeping plants compact. It is the best type of light to be used as a primary light source (if no or little natural sunlight is available). The average lifespan is about 10,000 cumulative hours. The bulb will light up beyond this time but due to the gradual decline of light, it is not worth your while to wait for the bulb to finally burn out. If you compare their lumen (brightness) per unit of energy consumed, metal halides produce up to 125 lumens per watt compared to 39 lumens per watt with standard fluorescent lights and 18 lumens per watt for standard incandescent bulbs. View MH & HPS grow lights
High Pressure Sodium - HPS HPS Plant Grow Light
High pressure sodium bulbs emit an orange-red glow. This band of light triggers hormones in plants to increase flowering/budding in plants. They are the best grow lights available for secondary or supplemental lighting (used in conjunction with natural sunlight). This is ideal for greenhouse growing applications.
Not only is this a great flowering light, it has two features that make it a more economical choice. Their average lifespan is twice that of metal halides, but after 18,000 hours of use, they will start to draw more electricity than their rated watts while gradually producing less light. HPS bulbs are very efficient. They produce up to 140 lumens per watt. Their disadvantage is they are deficient in the blue spectrum. If a gardener were to start a young plant under a HPS bulb, she/he would see impressive vertical growth. In fact, probably too impressive. Most plants would grow up thin and lanky and in no time you will have to prune your plant back before it grows into the light fixture. The exception to this is using HPS grow lights in a greenhouse or in conjunction another light source that emits light in the blue spectrum. Light sources that have a high output in the blue spectrum like sunlight and MH grow lights offset any stretching caused by HPS bulbs. View MH & HPS grow lights
Fluorescent Plant Grow Lights
Until recently, fluorescent grow lights have had a low output and have been too big and bulky to be of much use as a grow light for anything more than starting seedlings. CFL and T5 full spectrum fluorescent lights have changed that. At 75 to 90 lumens per watt, these lights are energy efficient and extremely effective especially when used in numbers. Fluorescent grow lights also have better color rendering properties (more of the light emitted is used by the plant) and produce much less heat than incandescent and HID grow lights. This allows them to be placed closer to plants (within a few inches) greatly decreasing lumen loss from the bulb to the plant. It is recommended that these lights be placed no more than a couple feet from the plants for best results. 2700k to 3000k bulbs provide higher output in the red spectrum which promotes flowering. 5000k to 6500k bulbs are full spectrum with much of the light in the blue spectrum which promote overall green plant growth. View (CFL) compact fluorescent grow lights, View T5 fluorescent tube grow lights
The standard T12 bulbs full spectrum tubes are fine for starts and seedlings and are popular for growing low-light plants like herbs and African violets. These lights are inefficient and are be replaced with high efficiency T5 lights which are a better light source for flowering and budding applications as well. View T5 fluorescent grow lights
Incandescent Plant Grow Lights
These lights are the most inexpensive to purchase but are also the most inefficient and a poor source of light for plants. At best they can provide supplemental light to individual house plants. Incandescent lights have a low lumen output per watt compared to HID and fluorescent grow lights. New smaller CFL grow lights like our 40 watt Green Thumb system produce as much light as a 150 watt incandescent bulb, and more of the light is used by the plant. This type of bulb will pay for itself in energy savings the first 60 days of use.
LED Plant Grow Lights
LED grow lightsLED grow lights are the newest lighting option for plants. They are advertised to be the most efficient and coolest running grow lights available. We have tested several different types of LED grow lights and have found none that outperform much cheaper fluorescent grow lights of similar wattage. LED plant grow lights are also not recommended for use with plants that you want to be viewed, because they give plants an unnatural appearance when the light is on.
***
Not all light is the same. Plants respond differently to different colors of light.
Light on either end of the spectrum, blue light or red light, have the greatest impact on photosynthesis.
Red light, on the opposite end of the spectrum, triggers a hormone response which creates blooms.
Grow lights producing the orange and reddish light typically produce substantial heat, however, some lights are able to produce full spectrum light without the heat.
As a general rule, inexpensive lights to purchase tend to be the most expensive to operate and the least effective. While price is not necessarily an indicator of performance, many of the efficient grow lights require ballasts as well as specialized fixtures.
Incandescent Lights.
The least expensive lights to purchase cost around $30. These incandescent lights work well for specific plants where the light is placed a minimum of 24” from the plant. These lights get extremely hot so they must be used with care. Spot grow bulbs, color corrected incandescent lights, install easily and are good for use with a specific plant or a small grouping of plants. Most spot incandescent bulbs last less than 1,000 hours. Some light fixtures come with a clip handle so you can put them exactly where they’re needed.
Fluorescent Grow Lights.
They are a common choice for homeowners. Fluorescent lights are reasonably energy efficient and relatively easy to install. A typical fluorescent bulb will last approximately 20,000 hours. Fluorescent light is typically on the blue end of the spectrum. Blue light encourages bushy compact growth which makes them perfect for seed starting. Blue light is also cool to the touch making it possible to place lights within just a few inches of the seedlings.
New Full-Spectrum Fluorescent Lights.
Provide the red spectrum as well to encourage blooming.
Combining the lights in a fixture makes for even, all around growth.
The next generation in fluorescent lighting includes the new T-5 lights.
These new lights have extremely high output but are energy efficient and long lasting.
The T-5 lights triple the light output of normal fluorescent lights without increasing the wattage. Plants absorb a high percentage of T-5 lighting because the fixtures function well very close to plants. High output bulbs require a high output fixture to operate, so the bulbs and normal fluorescent fixtures will not work together.
LED Lights
The newest type of grow lights use LED technology.
One major advantage to the LED lights is the small size.
LED lights are only a few inches in diameter and are easy to mount.
In some greenhouses, LED lights may be the only practical light option.
Hanging most grow lights requires a strong greenhouse structure and a place to hang the lights.
LED lights weigh a fraction of other lights and are easy to configure where needed. According to LED manufacturers, LED grow lights maximize blue and red light to provide and excellent balance for plants.
They do not have much green-yellow light. Since humans see green-yellow light best LED grow lights appear dim to our eyes. This is an exciting new technology that will be interesting to watch as it develops.
Now that I’ve given you a good rundown on greenhouse lighting options, it’s also important to mention darkness.
Almost all plants benefit from a period of six hours or more of darkness.
It’s a good idea to know how much light your plants need, but unlike commercial growers, hobbyists often have a wide variety of plants so they need to take a broad approach to lighting.
Fluorescent lights offer excellent overall lighting options.
Other Considerations
If you chose to use any type of fluorescent lighting, you will need to account for plant growth.
Fluorescent lights perform best when positioned very close to plants.
As plants grow into the light, it is important to raise the fixture.
Generally only the plants touching the lights will burn, but be prepared because they grow quickly.
Adjustable hangers are a good solution. These hangers move easily allowing you to make quick adjustments.
***
These bulbs pass electricity through a glass or ceramic tube containing a mixture of gases. The blend of gases determines the color of the light given off by each type of lamp. HID lights are twice as efficient as fluorescent lamps; one 400-watt HID lamp emits as much light as 800 watts of fluorescent tubing. All HID lights can run on regular 120-volt household current but they require special fixtures with ballasts.
Two Types of HID Lights
There are two categories of HID lamps: metal halide (MH) and high-pressure sodium (HPS). Both emit a much more intense light than fluorescent bulbs, which also pass electricity through a gas-filled tube.
MH bulbs emit light that's strongest at the blue end of the spectrum. It's a stark, cool white light that produces compact, leafy growth. Because the light does not distort the colors of the plants and people it illuminates, this type of plant grow light is a good choice for a light display in a living area.
Agrosun gold halide bulbs are color-corrected to give off more red/orange light than regular metal halides. This helps boost flowering in addition to supporting compact foliar growth. Halide bulbs should be replaced about once a year.
HPS bulbs last slightly longer; they should be replaced every 18 months. They emit light strong at the red/orange end of the spectrum, which promotes flowering. However, HPS lighting may also produce leggy growth unless used together with daylight or a metal halide system.
If your goal is lots of bloom, use high-pressure sodium lamps, but be advised: Their light has a red/orange cast that distorts the colors of everything they illuminate. This plant grow light is not flattering in a living room; everyone looks slightly jaundiced.
Grow Light Test Garden Tip:
You can use both high-pressure sodium and metal halide bulbs in a single location, but a metal halide bulb cannot be used in a high-pressure sodium fixture, and vice versa. HPS ballasts include an igniter and MH ballasts do not. If you have multiple fixtures, consider a combination of HPS and MH systems. If you have only one fixture, you can use a conversion bulb, using metal halide to promote foliage growth, then switching to a conversion high-pressure sodium bulb to encourage flowering.
Fluorescent Grow Lights
Traditional fluorescent tubes are the most economical choice if you're going to use grow lights. They can be used in inexpensive shop light fixtures or multitier growing carts.
The light produced by fluorescent tubes is much less intense than the other choices, so you are more limited in what you can grow. If you're just trying to supplement natural light rather than replace it, fluorescent light may be a good option.
Fluorescent tubes come in cool, warm, or full-spectrum. Light from cool tubes has a blue cast, while warm tubes emit a pink/white light. Full-spectrum tubes closely approximate the color of natural daylight. Full-spectrum bulbs are a bit more expensive but many growers consider them worth the price since the color of the light doesn't distort the color of your plants.
Less light is emitted from the ends of the fluorescent tubes than from the center. Plants with lower light needs should be placed under the 3 inches of tube at either end of the fixture.
Fluorescent tubes should be replaced every 18 months if they are being used approximately 16 hours per day.
Our Formula
First, determine how much space you need to illuminate. As a rule, you want 20 to 40 watts per square foot. Then divide the wattage of your bulb by 20 (such as 1,000 ÷ 20 = 50), then divide the wattage of your bulb by 40 (1000 ÷ 40 = 25).
The answer gives you the extremes of your light intensity range. With one 1,000-watt system, you can light between 25 and 50 square feet of interior landscape, depending on the plants and their light requirements.
Adjust your setup as you observe how well your plants grow, and increase or decrease the intensity of the light accordingly. This can be done by shifting the placement of your plants or light fixture so they are closer together or farther apart, but not by changing the bulb in your lamp to a bulb with more watts.
Each lamp is designed for a specific wattage and a 400-watt bulb cannot operate safely in a 250-watt system.
When starting growing plants indoors, one of the most important factors is light. Sure, you'll want to choose a good growstarting mix and establish a good watering routine, but proper lighting is crucial for healthy, stocky seedlings. The good news is that artificial lights, when used correctly, can give seedlings all the light they need to thrive.
The Key Points When Growing Plants Indoors Under Lights
Light Intensity
Seedlings require lots of bright light, and when they don't receive enough of it they get tall and leggy. In most cases, even the sunniest windowsill will not provide the intensity of light they need. The best solution is to grow your seedlings under fluorescent lights.
Growing plants under lights, lets you control light intensity in two ways: the wattage of the bulb and how close the bulb is to the plant's foliage. Fluorescent bulbs are ideal for seedstarting because they give off very little heat. This means you can provide high light intensity by positioning the bulbs just 2-3″ above the foliage. Regular incandescent bulbs are not used for growing seedlings because they give off too much heat and can burn tender foliage.
As your seedlings grow, the fluorescent light fixture should be raised about once a week to maintain a 3-4″ distance between bulb and foliage. A light stand with one or more adjustable fixtures makes this task easy.
Duration of Light
Most vegetables are "long-day" plants, which mean they require 14 to 18 hours of sunlight (or artificial light) each day. A rest period is equally important for healthy growth, so be sure your seedlings also get at least eight hours of darkness. Using an automatic timer is the best way to ensure that the lights are on for the right amount of time each day.Color of Light
Natural sunlight is the ideal light for starting seedlings, but with full-spectrum light bulbs, you can come pretty close. Full-spectrum fluorescent bulbs replicate approximately 94 percent of the solar spectrum. Recent innovations in fluorescent bulb technology have resulted in new-style bulbs that are lower in profile and higher in efficiency than standard fluorescent bulbs. That said, standard cool-white fluorescent bulbs will work just fine for starting seeds.***
Best Light for Growing Plants Indoors
Horticultural lighting systems allow you to extend the growing season by providing your plants with an indoor equivalent to sunlight. This is a great advantage for those of you who appreciate having a year-round supply of fresh flowers, veggies and herbs. Artificial lighting is also a great way to jump-start spring by starting your seedlings months ahead of the last frost. There are three main types of horticultural lighting systems.
HID (High Intensity Discharge) Plant Grow Lights
HID lighting is the most efficient way to convert electricity into light that is available to the consumer. There are two types of HID grow lights used for horticultural lighting:
MH Plant Grow Light - ACFMetal Halide - MH
Metal halide bulbs produce an abundance of light in the blue spectrum. This color of light promotes plant growth and is excellent for green leafy growth and keeping plants compact. It is the best type of light to be used as a primary light source (if no or little natural sunlight is available). The average lifespan is about 10,000 cumulative hours. The bulb will light up beyond this time but due to the gradual decline of light, it is not worth your while to wait for the bulb to finally burn out. If you compare their lumen (brightness) per unit of energy consumed, metal halides produce up to 125 lumens per watt compared to 39 lumens per watt with standard fluorescent lights and 18 lumens per watt for standard incandescent bulbs. View MH & HPS grow lights
High Pressure Sodium - HPS HPS Plant Grow Light
High pressure sodium bulbs emit an orange-red glow. This band of light triggers hormones in plants to increase flowering/budding in plants. They are the best grow lights available for secondary or supplemental lighting (used in conjunction with natural sunlight). This is ideal for greenhouse growing applications.
Not only is this a great flowering light, it has two features that make it a more economical choice. Their average lifespan is twice that of metal halides, but after 18,000 hours of use, they will start to draw more electricity than their rated watts while gradually producing less light. HPS bulbs are very efficient. They produce up to 140 lumens per watt. Their disadvantage is they are deficient in the blue spectrum. If a gardener were to start a young plant under a HPS bulb, she/he would see impressive vertical growth. In fact, probably too impressive. Most plants would grow up thin and lanky and in no time you will have to prune your plant back before it grows into the light fixture. The exception to this is using HPS grow lights in a greenhouse or in conjunction another light source that emits light in the blue spectrum. Light sources that have a high output in the blue spectrum like sunlight and MH grow lights offset any stretching caused by HPS bulbs. View MH & HPS grow lights
Fluorescent Plant Grow Lights
Until recently, fluorescent grow lights have had a low output and have been too big and bulky to be of much use as a grow light for anything more than starting seedlings. CFL and T5 full spectrum fluorescent lights have changed that. At 75 to 90 lumens per watt, these lights are energy efficient and extremely effective especially when used in numbers. Fluorescent grow lights also have better color rendering properties (more of the light emitted is used by the plant) and produce much less heat than incandescent and HID grow lights. This allows them to be placed closer to plants (within a few inches) greatly decreasing lumen loss from the bulb to the plant. It is recommended that these lights be placed no more than a couple feet from the plants for best results. 2700k to 3000k bulbs provide higher output in the red spectrum which promotes flowering. 5000k to 6500k bulbs are full spectrum with much of the light in the blue spectrum which promote overall green plant growth. View (CFL) compact fluorescent grow lights, View T5 fluorescent tube grow lights
The standard T12 bulbs full spectrum tubes are fine for starts and seedlings and are popular for growing low-light plants like herbs and African violets. These lights are inefficient and are be replaced with high efficiency T5 lights which are a better light source for flowering and budding applications as well. View T5 fluorescent grow lights
Incandescent Plant Grow Lights
These lights are the most inexpensive to purchase but are also the most inefficient and a poor source of light for plants. At best they can provide supplemental light to individual house plants. Incandescent lights have a low lumen output per watt compared to HID and fluorescent grow lights. New smaller CFL grow lights like our 40 watt Green Thumb system produce as much light as a 150 watt incandescent bulb, and more of the light is used by the plant. This type of bulb will pay for itself in energy savings the first 60 days of use.
LED Plant Grow Lights
LED grow lightsLED grow lights are the newest lighting option for plants. They are advertised to be the most efficient and coolest running grow lights available. We have tested several different types of LED grow lights and have found none that outperform much cheaper fluorescent grow lights of similar wattage. LED plant grow lights are also not recommended for use with plants that you want to be viewed, because they give plants an unnatural appearance when the light is on.
***
How to Select the Best Grow Light for Indoor Growing
Not all light is the same. Plants respond differently to different colors of light.
Light on either end of the spectrum, blue light or red light, have the greatest impact on photosynthesis.
Kinds of Light for Grawing
Blue light, referred to as cool light, encourages compact bushy growth.Red light, on the opposite end of the spectrum, triggers a hormone response which creates blooms.
Grow lights producing the orange and reddish light typically produce substantial heat, however, some lights are able to produce full spectrum light without the heat.
As a general rule, inexpensive lights to purchase tend to be the most expensive to operate and the least effective. While price is not necessarily an indicator of performance, many of the efficient grow lights require ballasts as well as specialized fixtures.
Basic Types of Grow Lights
These lights run the gamut of performance and price range.Incandescent Lights.
The least expensive lights to purchase cost around $30. These incandescent lights work well for specific plants where the light is placed a minimum of 24” from the plant. These lights get extremely hot so they must be used with care. Spot grow bulbs, color corrected incandescent lights, install easily and are good for use with a specific plant or a small grouping of plants. Most spot incandescent bulbs last less than 1,000 hours. Some light fixtures come with a clip handle so you can put them exactly where they’re needed.
Fluorescent Grow Lights.
They are a common choice for homeowners. Fluorescent lights are reasonably energy efficient and relatively easy to install. A typical fluorescent bulb will last approximately 20,000 hours. Fluorescent light is typically on the blue end of the spectrum. Blue light encourages bushy compact growth which makes them perfect for seed starting. Blue light is also cool to the touch making it possible to place lights within just a few inches of the seedlings.
New Full-Spectrum Fluorescent Lights.
Provide the red spectrum as well to encourage blooming.
Combining the lights in a fixture makes for even, all around growth.
The next generation in fluorescent lighting includes the new T-5 lights.
These new lights have extremely high output but are energy efficient and long lasting.
The T-5 lights triple the light output of normal fluorescent lights without increasing the wattage. Plants absorb a high percentage of T-5 lighting because the fixtures function well very close to plants. High output bulbs require a high output fixture to operate, so the bulbs and normal fluorescent fixtures will not work together.
LED Lights
The newest type of grow lights use LED technology.
One major advantage to the LED lights is the small size.
LED lights are only a few inches in diameter and are easy to mount.
In some greenhouses, LED lights may be the only practical light option.
Hanging most grow lights requires a strong greenhouse structure and a place to hang the lights.
LED lights weigh a fraction of other lights and are easy to configure where needed. According to LED manufacturers, LED grow lights maximize blue and red light to provide and excellent balance for plants.
They do not have much green-yellow light. Since humans see green-yellow light best LED grow lights appear dim to our eyes. This is an exciting new technology that will be interesting to watch as it develops.
The Best Grow Light Option
Now that I’ve given you a good rundown on greenhouse lighting options, it’s also important to mention darkness.
Almost all plants benefit from a period of six hours or more of darkness.
It’s a good idea to know how much light your plants need, but unlike commercial growers, hobbyists often have a wide variety of plants so they need to take a broad approach to lighting.
Fluorescent lights offer excellent overall lighting options.
Other Considerations
If you chose to use any type of fluorescent lighting, you will need to account for plant growth.
Fluorescent lights perform best when positioned very close to plants.
As plants grow into the light, it is important to raise the fixture.
Generally only the plants touching the lights will burn, but be prepared because they grow quickly.
Adjustable hangers are a good solution. These hangers move easily allowing you to make quick adjustments.
***
Growing Plants Indoors with Artificial Light
HID Plant Grow Lights
The brightest grow lights are high-intensity discharge (HID) lights. They can be installed anywhere in your home, garage, or greenhouse to supplement existing light, and they can serve as the sole source of light for your plants.These bulbs pass electricity through a glass or ceramic tube containing a mixture of gases. The blend of gases determines the color of the light given off by each type of lamp. HID lights are twice as efficient as fluorescent lamps; one 400-watt HID lamp emits as much light as 800 watts of fluorescent tubing. All HID lights can run on regular 120-volt household current but they require special fixtures with ballasts.
Two Types of HID Lights
There are two categories of HID lamps: metal halide (MH) and high-pressure sodium (HPS). Both emit a much more intense light than fluorescent bulbs, which also pass electricity through a gas-filled tube.
MH bulbs emit light that's strongest at the blue end of the spectrum. It's a stark, cool white light that produces compact, leafy growth. Because the light does not distort the colors of the plants and people it illuminates, this type of plant grow light is a good choice for a light display in a living area.
Agrosun gold halide bulbs are color-corrected to give off more red/orange light than regular metal halides. This helps boost flowering in addition to supporting compact foliar growth. Halide bulbs should be replaced about once a year.
HPS bulbs last slightly longer; they should be replaced every 18 months. They emit light strong at the red/orange end of the spectrum, which promotes flowering. However, HPS lighting may also produce leggy growth unless used together with daylight or a metal halide system.
If your goal is lots of bloom, use high-pressure sodium lamps, but be advised: Their light has a red/orange cast that distorts the colors of everything they illuminate. This plant grow light is not flattering in a living room; everyone looks slightly jaundiced.
Grow Light Test Garden Tip:
You can use both high-pressure sodium and metal halide bulbs in a single location, but a metal halide bulb cannot be used in a high-pressure sodium fixture, and vice versa. HPS ballasts include an igniter and MH ballasts do not. If you have multiple fixtures, consider a combination of HPS and MH systems. If you have only one fixture, you can use a conversion bulb, using metal halide to promote foliage growth, then switching to a conversion high-pressure sodium bulb to encourage flowering.
High-Intensity Fluorescent Grow Lights
High-intensity fluorescent bulbs are also an excellent choice. Fixtures resemble those of HID bulbs, but they are less expensive, and cool and warm bulbs are available that fit in the same ballast. Choose according to which light is more appealing to your eye.Fluorescent Grow Lights
Traditional fluorescent tubes are the most economical choice if you're going to use grow lights. They can be used in inexpensive shop light fixtures or multitier growing carts.
The light produced by fluorescent tubes is much less intense than the other choices, so you are more limited in what you can grow. If you're just trying to supplement natural light rather than replace it, fluorescent light may be a good option.
Fluorescent tubes come in cool, warm, or full-spectrum. Light from cool tubes has a blue cast, while warm tubes emit a pink/white light. Full-spectrum tubes closely approximate the color of natural daylight. Full-spectrum bulbs are a bit more expensive but many growers consider them worth the price since the color of the light doesn't distort the color of your plants.
Less light is emitted from the ends of the fluorescent tubes than from the center. Plants with lower light needs should be placed under the 3 inches of tube at either end of the fixture.
Fluorescent tubes should be replaced every 18 months if they are being used approximately 16 hours per day.
How to Determine Plant Grow Light Wattage
Once you've decided which kind of plant grow light you want, it's time to decide how big a bulb you need for the space you have.Our Formula
First, determine how much space you need to illuminate. As a rule, you want 20 to 40 watts per square foot. Then divide the wattage of your bulb by 20 (such as 1,000 ÷ 20 = 50), then divide the wattage of your bulb by 40 (1000 ÷ 40 = 25).
The answer gives you the extremes of your light intensity range. With one 1,000-watt system, you can light between 25 and 50 square feet of interior landscape, depending on the plants and their light requirements.
Adjust your setup as you observe how well your plants grow, and increase or decrease the intensity of the light accordingly. This can be done by shifting the placement of your plants or light fixture so they are closer together or farther apart, but not by changing the bulb in your lamp to a bulb with more watts.
Each lamp is designed for a specific wattage and a 400-watt bulb cannot operate safely in a 250-watt system.
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