start seeds under indoor lights Seeds & Seed Starting

Growing Seedlings Under Indoor Grow Lights

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growing seedlings under lightsUpdated 02/09/24

Successfully growing plants from seeds requires the best light for seedlings, and understanding whether to use blue or red light can make a significant difference.

Many gardeners don't have the luxury of a south-facing window with 12+ hours of sunlight, making indoor grow lights for seedlings essential.

This guide will enlighten you about the ideal light spectrum for seedlings and how close the light should be for optimal growth. It offers insights into choosing the right indoor lighting system to ensure a bounty of robust, green seedlings.

Light Color

Light color, also known as color temperature, plays a crucial role in plant growth, especially when considering blue or red light for seedlings.

Cool light refers to the blue end of the spectrum, vital for vegetative growth, while warm light indicates the red end, essential for flowering and fruiting.

Sunlight, providing the complete spectrum including all rainbow colors, is ideal, but when growing indoors, selecting the optimal grow lights for seedlings is key.

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

The debate around the ideal duration of supplemental light for seedlings includes the question: do seedlings need 24-hour light?

While most vegetables and garden plants require 16 to 18 hours of light daily to avoid becoming pale and leggy, some growers argue for the benefits of continuous, 24-hour light exposure for seedlings.

This approach, however, may not apply to full-grown plants. Using a timer for a 16-hour light cycle can be a practical solution for those who prefer not to leave grow lights on constantly.

How Close Should Light Be To Seedlings

Determining the correct distance between grow lights and seedlings is crucial for healthy growth.

If lights are too close, they can scorch delicate seedlings; too far, plants may become leggy as they stretch toward the light.

The ideal distance varies based on the type of light used. For instance, LED lights, due to their lower heat output, can be placed closer than hotter lights like incandescent.

Generally, a safe distance is about 2-4 inches above the seedlings, but it's important to adjust this based on the plant's response and the light's heat and intensity.

Monitoring and adjusting the light position as the seedlings grow is key to ensuring robust and healthy plants.

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.

stacked grow kit

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.

Related Review: SunLite Garden full-spectrum grow lights and stand

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.

Growing Tips

  • Rotate your plants each week. The light from a fluorescent bulb is more intense at the center of the bulb than it is at the ends.
  • Replace fluorescent tubes when the ends darken. That means the tube is old and the light output may be less than half of a new bulb.
  • Clean your fluorescent bulbs each month. Dust and dirt can dramatically decrease the amount of light emitted.
  • Place your hand where the light hits the foliage. If you feel any warmth, the light is too close.
  • Move the lamp upward as the seedlings grow; you want to keep the lights about 2-4 inches above the plants.

Good Options for Indoor Grow Lights

No products found.

Three Tier Stand SunLite Grow Kit
This kit, also from Gardener's Supply Company, comes in various configurations, from a single level to this 3-tier version. I've been using the tabletop version of this for over 6 years and have been very happy with it.
Farm 10101-10135-1 All-Purpose LED Grow Light
If you're looking for an LED grow light kit, this one provides everything you need. The company also seeds seed starting trays and fertilizers.
SunBlaster SBL1600200 Grow Light Garden
This is a smaller, non-expandable kit that I've used for many years.

 

 

Video Resources

YouTube Seed Starting Sowing

How to Successfully Start Seeds Indoors - This video tutorial shows you exactly how to successfully start seeds indoors, including seed starting mix, containers, sowing, watering, heat, and more.

>> Watch the video on our YouTube channel (28 minutes)

Seeds Have Germinated: Now What? How to Care for Seedlings - After your seeds have germinated what do you do next to grow healthy, stocky seedlings? In this video I cover lighting, watering, fertilizing, airflow, thinning, transplanting and hardening off.

>> Watch the video on our YouTube channel (29 minutes)

Last update on 2024-03-28 / Affiliate links / Images from Amazon Product Advertising API

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