Whether you want to grow houseplants, flowers, or even edibles, providing the right amount of light can often present a challenge to indoor gardening.
To have a thriving indoor garden, it’s a good idea to learn about the different types of plant grow lights and how you can best use them. This includes knowing about different light temperatures and colors, the lighting technology available, and the setup and exposure time.
Temperature and Color
Light has a temperature measured in Kelvin. You’ll find that most light bulbs are marked with a temperature such as 2000K or 4000K. The higher the number, the “cooler” the light appears.
For your plants, you want a light that imitates natural sun-lit conditions. Sunlight can have a temperature of 5000K or more, and contains all the colors of the visible spectrum. However, this temperature can differ throughout the day and in different seasons, so it can get a bit tricky picking the best light for your plants.
A lot of people recommend a cooler light for vegetation (5000K to 6500K), and a warmer light for flowering stages (around 3000K), but a neutral temperature of 4000K is great for most situations.
Many grow lights available use blue and red light only, and are thus a magenta color. This is because they’re typically cheaper to make, and it also comes from the myth that plants don’t need green light to grow.
Just because most plants appear green to us, doesn’t mean they reflect all green light! Some of the green light penetrates into the deeper parts of leaves, and is absorbed. Unlike blue and red light which is only absorbed in the outermost layer.
Natural sunlight contains all the colors of the spectrum, and studies show that this is exactly what plants need. A light that covers the entire color spectrum should appear white to the human eye.
Some companies use magenta lights, supplemented with white lights to fill the missing spectrum of light. This is an efficient way to match the absorption patterns of various plants.
Light Technology
There are three main types of technologies being used for growing lights, each with varying positives and negatives. These are Compact Fluorescent Lighting (CFL), High-Intensity Diode (HID), and Light Emitting Diode (LED).
There are other types available, but they are experimental and less common.
Compact Fluorescent Lighting (CFL)
Common household Fluorescent lights (known as T12) can be used as growing lights, but they have low intensity so they need to be placed very close to the plant. T5 fluorescent lights have a higher intensity and are thus more ideal.
Another option is the Compact Fluorescent Bulbs (CFB), which are great for smaller spaces and can be fitted into common light fixtures.
Generally, fluorescent lights are useful if you only have a few plants, but if you need to grow a lot of plants, you’ll need a stronger light.
High-Intensity Diode (HID)
Also known as High-Intensity Discharge Lights. These lights are the most commonly used by professional growers. They’ve been around for a long time, and are known to produce the fastest growth rates and the best yield/m2. The reason for this is that they produce the most usable light spectrum for the plants.
There are two types of HIDs commonly used for growing. The first is High-Pressure Sodium (HPS), which is used for the flowering stage, and Metal Halides (MH) which is used for the vegetation. If you have to pick one only, choose the HPS, as they cover most of the light spectrum and are therefore more suited for the entire lifecycle of plants.
HID lights are cheaper than LEDs, but they have many drawbacks. For example, they require extra equipment to run (such as a ballast and reflectors), and they use up a lot of electricity, so they aren’t the best choice for the environment and will cost more to run.
They also produce a lot of heat, so good ventilation is required for them. HIDs have a low lifespan and will need to be replaced every 3-5 grows. Despite all these problems, they’re the 1st choice of professionals simply because of their yield.
Light Emitting Diode (LED)
LED lights are more expensive than CFL and HID lights, but they’re also more efficient and cheaper in the long run. They use half the power and last five-to-ten times longer compared to fluorescent lights, and they produce the least heat. LEDs are better for the environment because they don’t contain mercury.
These features make LED lights the most efficient for growing large quantities of plants with an acceptable yield.
Avoid low priced LEDs as they won’t produce the desired growth or yield. Good quality LEDs are expensive to make.
Comparison Chart
Light Technology | Compact Fluorescent Light (CFL) | High-Intensity Diode (HID) | Light Emitting Diode (LED) |
|---|---|---|---|
Price | Lowest | Low | High |
Lifetime | Medium | Low | High |
Yield/m2 | Low | High | Medium |
Power usage | Medium | High | Low |
Heat output | Low | High | Lowest |
Intensity | Low | High | Medium |
Accessories | None | Ballast and reflectors | May need reflectors |
Difficulty | Lowest | High | Low |
Environmental impact | High | High | Low |
Recommended type | T5 | High-Pressure Sodium (HPS) | Any type that’s newer/more expensive |
Newer technologies of grow lights are emerging, such as Sulphur Plasma Lights (SPL), and induction lighting. These technologies are experimental, expensive, and not widely available, so there’s little information about their effectiveness.
Grow Light installation
Different species of plants require different amounts of light. Plants that are native to tropical jungles or shady conditions may not require much light, while plants from a desert environment would require a lot.
Edible plants generally require a lot of light, especially fruiting plants. A good rule of thumb is to research the plant’s native habitat and simply try to imitate it.
Distance and Intensity
You can control how much light reaches the plant with various factors, including what type of light is used, how many, and the distance between the light source and the plants.
Read the wattage number indicated on your light bulb’s packaging. Low-light plants require as little as 10 watts per square foot.
Medium-light plants may need about 15 watts per square foot. 30 watts per square foot is acceptable for edible plants, but a flowering fruit species may require up to 50 watts per square foot.
Additionally, HID lights are often dimmable, which is the simplest way to change intensity.
On average, fluorescent lights should be placed within 3-12 inches away from the plant, while an LED can be placed 12-24 inches, and HIDs can go anywhere from 24-60 inches.
Light Tracks
Consider some kind of track or pulley system to support the lights above your plants, and still be able to adjust the height to match the plants’ current size. These lighting systems can be makeshift or ready-made, and they can get really creative and be incorporated into your decor.
Timing
Whether in nature or indoors, plants require times of total darkness to respire. Indoor plants need more light hours than outdoor plants, with 12 to 18 hours being a good range for most plants.
You can use a timer to automatically turn the lights on and off as needed.
Don’t forget to look up how long each species of plants should be exposed to light, which can differ drastically depending on their native habitat. These can be categorized as follows:
Never leave your plants in the light 24/7. The excess light will only exhaust them and limit their growth. Most plants need at least 8 hours of total, uninterrupted darkness.
Summary
Indoor gardening can be a fun, relaxing hobby. Maintaining the right amount of sun exposure for your plants can be a little tricky, but you can get started immediately with just a few pointers.
If you’re not sure what light temperature to choose, a full-spectrum white light with a temperature of 4000K is great for most situations. If possible, use a cool (6500K) temperature during vegetation, and a warm (3000K) temperature for blooming.
Choose between CFL, HID, and LED lights. CFL (Fluorescent) lights are the most beginner-friendly, with a T5 being the most appropriate CFL for plants.
Research the unique needs of the plants you choose to grow, and calculate how much light they need, including the intensity and exposure time. Use a timer to make sure your plants receive the correct light-to-dark hour ration, depending on the species.
Additionally, don’t use a red-blue light only, because your plants still need green light. Don’t bother investing too much in lighting equipment without researching how they work, as you only need a few things to get started. Finally, don’t leave your plants exposed to light 24/7.
With these takeaways, you could have a thriving, private garden that you can be proud of.
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