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Growing Seedlings Under Indoor Grow Lights

Anyone who’s tried growing plants from seed knows that proper lighting is critical to producing an abundance of stocky, green seedlings. For those of us lucky enough to have a south-facing window with 12+ hours of full sun, lighting isn’t an issue. But for the rest of us, an indoor lighting system of some kind is a necessity.

This primer on indoor lighting for seed starting will help you choose the options that work best for you.

Light Color

Light color is also referred to as color temperature, with cool light describing the blue end of the spectrum and warm light being the red end. Sunlight contains the complete spectrum of light, including all colors of the rainbow.

Although plants use the full spectrum for photosynthesis, red and blue light seem to be most critical. Red light stimulates vegetative growth and flowering (but if a plant gets too much, it will become tall and spindly). Blue light regulates plant growth, which makes it ideal for growing foliage plants and short, stocky seedlings (but too much will result in stunted plants).

You can tell which color a grow light produces by looking at its Kelvin rating. Lamps with a rating of 5000 Kelvins will appear bluish, while those with a 2500 Kelvin rating will be reddish.

Light Intensity

The intensity of light that a plant receives is determined by the wattage of the bulb and the distance between the plant and the light source. So, for example, a brighter bulb that’s farther away from the plant could provide the same light intensity as a dimmer bulb that’s closer to the plant.

Different plants have different light intensity needs, but most seedlings grown for the garden will need higher intensity light to flourish. In general, the leaves should be about 2 – 4 inches away from the light source (assuming use of a fluorescent bulb – see below).

Duration of Light Exposure

There’s still debate about how many hours of supplemental light is ideal when starting seeds and growing plants indoors.

Most vegetables and garden plants require at least 16 to 18 hours of light each day; without enough light, they get pale and leggy. The conventional advice was to turn lights on for 16 hours each day. However, some growers maintain that 24 hours of consistent light every day provides a better outcome when growing seedling (i.e., there’s no need to give seedlings a nightly rest but this advice doesn’t necessarily apply to full-grown plants).

It’s certainly easier to leave your grow lights on all the time and that’s what I do. If you choose to go with 16 hours on, 8 hours off, put the lamp(s) on a timer so you won’t forget to turn the lights on or off.

Types of Bulbs

You can choose between incandescent, fluorescent, LED, and high-intensity discharge (HID) bulbs, each of which has its own pros and cons. Choose the grow light that works best for the type of plants you want to grow and where you plan to grow your seeds.

Incandescent Bulbs

These include halogen bulbs and are the type of light bulbs still used in most homes (although they’re getting harder to find now that stores are carrying only more efficient bulbs, such as CFLs and LEDs).

Incandescent bulbs are a good source of red light, but a poor source of blue, meaning that plants will likely become spindly when grown under incandescent light.

Incandescent bulbs, and especially halogen bulbs, also produce a lot of heat in relation to the amount of light they give off; plants growing too close to the bulb can be easily burned.

Generally speaking, these are not the best type of lamps for growing seedlings.

Fluorescent Bulbs

These types of bulbs produce two to three times more light than incandescent bulbs for the same amount of energy and are the most inexpensive lights for indoor gardening. However, they usually require bulky external ballasts (like, for example, overhead shop lights) so aren’t as easy to work with as incandescent and LED bulbs.

Cool white bulbs are a good source of blue and yellow-green light, but are a poor source of red light. Plants grown under cool white bulbs will be stocky or even slightly stunted. Warm white bulbs emit plenty of orange and red light, but less light in the blue and green spectrum. These bulbs, when used alone, result in tall, spindly plants. If you are growing seedlings under two-bulb fluorescent fixtures, you can usually achieve a good color balance by combining one cool white and one warm white bulb.

A set of stacked shelves with fluorescent T5 lamps (or LED lamps) makes it easier to grow a large number of seedlings.

Full-spectrum fluorescent bulbs produce a balance of cool and warm light that replicates the natural solar spectrum, although these are less energy efficient than other fluorescent bulbs and tend to produce more heat. But, given the wider range of light frequencies emitted by these bulbs, they are a good choice for growing seedlings.

T5 lamps are fluorescent lamps that are 5/8″ of an inch in diameter, making them much less bulky than typical fluorescent bulbs. These are the lamps you’re most likely to find in grow light kits.

When using fluorescent lamps, be sure that all plants get ample light. For a typical seedling tray, that means using 2 bulbs, ideally with a reflector hood over them to focus all the light on the seedlings below.

LED Grow Lamps

Unlike other bulbs which produce light across a broad spectrum, light-emitting diodes (LEDs) give off light within a narrow band. LEDs designed for growing plants emit light in the two bands that plants need – red and blue. The result is a purple glow that not everyone likes.

LEDs are mercury-free and won’t shatter like glass. These bulbs are long-lived (up to 5x longer than fluorescent lamps) and very energy efficient, but they cost considerably more than fluorescent bulbs.

Research is still ongoing to determine which combination of light frequencies are best for plant growth and how LED grow lights compare to fluorescent bulbs in producing healthy seedlings. I haven’t seen a definitive answer on this one yet but more and more companies are producing LED grow lights and seed-starting kits, and even commercial growers are slowly moving in that direction.

High-Intensity Discharge Lamps

These lamps are used by commercial growers and serious horticulturists. These energy-efficient bulbs generally emit twice the amount of light (lumens) as a fluorescent bulb. However, the bulbs and special fixtures are considerably more expensive than those needed for incandescent or fluorescent lights. They also tend to be high-wattage bulbs, so you need to be sure your electrical system can handle the load. Some of these lights burn so brightly that they must be located in a special room and you’ll need to wear eye protection when working around them.

Metal halide lights emit an intense, bluish-white light that is excellent for growing plants. The foliage stays green and vigorous, and plants are usually stocky and strong. Metal-halide lights are currently the number one choice for serious indoor gardeners. Mercury vapor lamps emit a bluish, relatively well-balanced, high-intensity light. High-pressure sodium bulbs are usually used to promote flowering and fruiting but, when used exclusively, they produce leggy, weak-stemmed plants.

What’s the best option?

For the average home gardener starting seedlings indoors, a fluorescent or LED lamp will usually be the best choice to ensure that your plants get the quality, intensity, and duration of light they need to stay in peak condition.

A description and comparison of different grow lights for starting seeds and growing plants indoors. Covers incandescent, fluorescent, LED and high intensity discharge lamps, as well as issues around light color, intensity and duration.

What is the precise amount of lumens every plant needs?

How many lumens do you need per plant?

When you are growing plants, flower or crops out in your own yard, there are certain necessities they should acquire. You need to supply the sufficient amount of water, air, and fertilizer to boost their growth. They would also be much healthier if you regularly expose them out in the sunlight. If all of these are adequately provided, your plants would grow healthy and in no time.

Winter could be a harsh season for growing plants. The temperature drops and the available hours of daylight may not be sufficient. As we all know, the sunlight is vital to the growth of the plants. So if this is not present and the plants do not receive the optimal amount of natural light during daytime, some issues may occur. What should you do?

Growing plants indoors could be your final resort, but you can still allot all their needs. This procedure can be as effective as the natural growing process if the proper measures are applied. When it comes to the sunlight exposure, you can be less concern about it. Grow lights  will help you provide the supplementary light for your plants.​

Now that you have the grow lights for your plants, how many lumens should you allocate for each plant? What is lumen in plants, anyway?

​What is the lumen in plants?

Lumen refers to a measure of the total amount of emitted visible light by a source. The total number of lumens varies according to the type of grow light, the type and number of plants, the total measurement of the area, the distance of the plants, and their height. If possible, you should also determine the current stage of your plant to know how much supplementary light you’d apply.

Moreover, if you have decided to continue the process indoors, it is a must to know the preferable amount of lumens every plant should receive. Determining the precise number of lumens prevents any damages on your plant. Thus, supplies the necessary optimal light for their productive growth.

Plant Lighting : Supply the Right Amount of Lumens​

Though grow lights have been an efficient tool for growing fruits and veggies indoors, note this may not be a good option for some crops. Squash, peas, beans, melons, cucumbers, corn or watermelons may not survive the artificial growing process indoors.

However, there are certain crops that thrive indoors especially when winter season comes. Potatoes, cauliflower, carrots, beets, onions, garlic, herbs, tomatoes , lettuces, broccoli, and spinach are some of the best choices. So if you are left with no choice but to grow them indoors with grow lights, how would you know the right amount of lumens per plant?

The basis for the total measurement would be lumens per square foot.

The figures listed below are based on the average lumens that are proven effective by many users. With this reference, a CFL or compact light fluorescent is used.

  1. The optimal light would be 7000 to 7500 lumens per square foot.
  2. If the plant only requires minimum lighting, it should be approximately 2000 lumens per square foot.
  3. For the mid-range measurement, it should be approximately 5000 lumens per square foot.
  4. The vegetative phase is when the plants carry out photosynthesis and other accumulating sources needed for the reproduction and flowering. If ever you are in the vegetative period, approximately 2000 to 3000 lumens per square foot would be the minimum amount.
  5. If your plants are on the flowering phase, 5000 to 10000 lumens per square foot is recommended.

NOTE : Results may still vary according to the number of plants, how far apart every crop is planted, the type of plant, the area size, and the grow light being used. Indoor air and temperature are also major factors that can affect the growth of your plants.

Gardening with Grow Lights

Due to the unceasing progress of technology, a lot of tools have been efficient for gardening indoors. Grow lights are one of the outstanding innovations that have been beneficial for growing plants. Though this is an artificial procedure, the results are as effective as the natural process. You just have to be keen with the details regarding the lumens or watts every plant needs.

However, you cannot also just rely on the intensity of light for a productive growth. To achieve the best outcome, there are certain things you should remember if you opt for this process.

  1. ​ Choose the right color . Plants respond to the spectrum of the light. The sunlight has the complete spectrum of lighting, such as rainbow colors, that is why all plants grow healthy and productively. Hence, full spectrum lights are highly recommended as they ensure the optimal lighting the plants need.
  2. Provide the right duration . Too much or too little may cause some complications to the plant’s growth. It is indeed important to know how long you should expose your plants under the grow lights. Kalanchoe, azaleas, begonias and chrysanthemums are some of the plants that should be under the light for 12 hours each day.

On the other hand, vegetable and flowering plants usually require 14 to 18 hours of light per day. African violets, foliage plants, geraniums and coleus are some of the plants that can be exposed under the grow lights for 8 to 12 hours per day.

Conclusion

Growing plants indoors may not be the best option for many users. However, if the season changes and the sunlight’s not available for growing the plants, you can try growing them indoors with the grow lights. Just make sure to remember how many lumens every plant needs to ensure their healthy growth. If want to measure using watts, there are also certain guidelines you need to follow.

Hope this article helps you as much as it did to me. If you have any thoughts and questions about it or any experiences you’d like to share, tell us through the comment box below!

If you are growing your plants under grow lights and still not certain how many lumens your plants need, this article will help you.