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Grow Lights Explained: Here’s What You’re Doing That’s Wrong

Grow Lights Explained: Here's What You’re Doing That's Wrong

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One of the most important considerations for indoor gardening is light. While some vegetables will chug along with a bare minimum of six hours of light daily, they will flourish with 12-16 hours daily. Clearly, grow lights are a must, especially during winter. However, one of the most common mistakes among indoors gardeners is using the wrong type of light.

Red, Blue, And Full-Spectrum Light

Let’s start by talking about the color in light. We perceive sunshine, for instance, as white light, but it’s actually made up of all the colors of the rainbow — it’s full-spectrum. Light bulbs don’t generate light the same way that the sun does, and the color of light they produce often appears as off-white. Traditional incandescent bulbs, for instance, give off a yellow-red glow, whereas basic fluorescent tubes often have a blue glow.

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Plants have different reactions to the different colors within light. Blue light encourages the growth of strong leafy plants, while red light helps plants flower and fruit. It helps to understand how plants react to red and blue light in order to choose the best grow lights for your indoor garden.

Fluorescent Grow Lights

Not that long ago, basic fluorescent tubes were the only real option for grow lights, and many gardeners still swear by them. They are inexpensive, easy to install, and energy efficient. And, with the advent of compact fluorescent light (CFL) bulbs, installation is easier than ever, since you can simply screw a bulb into any existing light fixture.

Grow Lights Explained: Here's What You’re Doing That's Wrong

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Fluorescent bulbs come in warm (red), cool (blue), and full-spectrum ranges. The light that fluorescents produce is relatively weak, but there are also high-intensity fluorescent bulbs if needed. Full-spectrum and high-intensity fluorescent bulbs are more expensive than basic ones, but they may end up being more cost-effective.

LED Grow Lights

Light emitting diodes (LED) bulbs have a lot of potential for grow lights, but they are not yet widely used. Like many technologies in their infancies, they are relatively expensive, although their cost is coming down. Keep your eye on LED grow lights because they have a lot of benefits, including having a long life and being energy efficient, and emitting little heat. Also, they can be programmed to produce specific wavelengths of light.

HID Grow Lights

There are two types of high-intensity discharge (HID) bulbs, both of which produce bright and intense light. Metal halide (MH) bulbs emit light that is quite similar to natural sunlight, without generating a lot of heat. However, they do tend to the blue end of the spectrum, and depending on the type of bulb used, you may need to supplement with high-pressure sodium (HPS) lighting, which emits red light. HPS bulbs are excellent to promote flowering and fruiting. However, both types of HID bulbs can only be used in special fixtures, with ballasts, and the complete set-up can be expensive.

Your Grow Light Set-Up

Indoor gardening requires light, but that light must be cool. The heat created by incandescent and halogen bulbs is too intense and will fry your seedlings. Stick with fluorescent, LED or HID lighting.

Consider where the grow lights will be placed in your house. If your plants are already getting a great deal of light from a south-facing window, then weaker bulbs (like basic fluorescents) will work fine as supplementary lighting. If your plants are in a darker area of your home, you will need more powerful grow lights, like high-intensity fluorescent or HID bulbs.

The distance between your plants and your light source depends on what kind of bulbs you use. Since fluorescents are weaker, they can be placed only 2-3 inches from your plants; but LEDs should be 12-18 inches away. Either way, you will need to adjust the height of your grow lights as your plants get taller. Don’t count on keeping the position of your lights static. Seedlings will grow tall and spindly, without putting out leaves, if they need to stretch toward a far-away light source; and, of course, you don’t want them to touch the bulb.

The most complicated part of creating a grow light system is figuring out how big — in terms of wattage — it needs to be. It’s not just about the square footage of your growing space, but also about the type of light you’re using and what you’re growing. You will need a higher wattage if you’re using weaker bulbs, or are growing light-loving plants. Lettuce, for instance, needs less light than tomatoes do. While it’s tempting to just go with a higher wattage to cover all contingencies, that can have a negative effect on your energy consumption. There are all kinds of online guides that can help you figure out how to tailor your wattage to your plants.

Grow lights aren’t rocket science, but they aren’t a trip to the candy store, either. To effectively use grow lights, it helps greatly to have some understanding of how plants react to light, and of the available bulb options. Once you have that knowledge, you can optimize your own grow light set-up so that it best suits your needs.

What advice would you add on using grow lights? Share your tips in the section below:

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  1. It makes sense about the behaviour of plants to the lightcolor.
    In spring, the sun is relatively low on the horizon.
    Making the sunlight more blueish (because of filtering by the atmosphere).
    In summer the sun is more straight above you, letting more red and yellow light pass then in winter/spring.
    In spring (triggered by the blueish light) the plants will be in growing mode.
    While the more yellowish/redish light in summer will trigger blooming and fruiting.

    • I hate to argue with you but your sunlight colouring is wrong. Think sunrise or sunset – the sun’s blue light is filtered out more due to the longer trip it has to make through the atmosphere, hence the beautiful red sunrises and sunsets. With the sun higher in the sky, the light has a shorter path through the atmosphere and therefore less of the blue light gets filtered out, which is why we see more of a blue sky.

  2. I started using LED grow lights with great success this past year. The first ones were 8 watt flood lights from the local hardware store for about $4 each. I strung eight of them in parallel about 8 inches over the plants. Then I wanted to experiment with individual LED’s. I have micro greens growing under full spectrum LED’s which are a combination red-blue color. Other micro greens are growing under white (6500k) LED’s. Advantages are lower operating cost and longer life . Disadvantages are non-existent so far. It is January in Michigan and I have a tomato plant and many peas growing in the basement as well.

    • Hey Don do a guy a favor when those tomatoes ripen throw me one across the border to ohio hahahah due to some problems I haven’t been able to plant a garden since 2014 and I Will not buy those flavorless baseballs they sell in the stores.

  3. Something I’ve been getting more and more questions about are ceramic metal halide systems. They fall under the HID umbrella, but CMH bulbs combine the spectrum of MH and HPS, so one bulb can be used for the entire grow. They also use less power and give off less heat and they last longer than HPS or MH. The one negative is that HPS bulbs are more powerful (in terms of lumen output), but to many, that is easily offset by CMH’s other advantages.

    Personally, I prefer LED grow lights. But many growers are reluctant to switch from HID. For them CMH makes the most sense.

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