Grow light for seedlings 

Grow light for seedlings 

Table of Contents

by Jille Kuipers

Ambient indoor light can be OK-ish to grow some microgreens. At a good spot, you might also be able to grow some herbs. For leafy greens and fruiting vegetables such as cucumbers and tomatoes, you’ll need lots of light. You either need a garden, balcony with good daylight or grow lights.

Grow lights help you get better seedlings

Good grow lights for seedlings will provide the right amount of light to support the development (plant organs, rooting) and growth (photosynthesis). The amount should be just right, too intense and the leaves will burn, too little and the plants will not develop well. The right light will give you healthy and vigorous seedlings that you can plant out in the vegetable garden or greenhouse. 

Twelve hours of light each day

Seeds can be started with ambient indoor light, but once they start growing up they need around twelve hours of light each day to develop good rooting and grow vigorously. 

Vigorous seedlings grown indoor will give you an earlier harvest

In regions with winters, it is often only after spring that the day length starts to become supportive enough for seedlings. Starting indoors with grow lights will give your seedlings a headstart so you can start immediately with strong plants when the outdoor temperature is suitable, rather than from seeds in your garden.  

Use linear lights or bulbs for seedlings at close distance

With the help of grow lights, you can provide the right amount of light to make seeds and seedlings feel like they’re out in the sun. Good grow lights contain all colors of the light spectrum with lots of deep red and blue as well as some green and white. Normal light bulbs are made for the human eye and they have little blue and deep red in them. This means seedlings develop in a suboptimal way and it can be a cause of thin growth. There are lights like a T5 or you can use grow light bulbs. Linear grow lights from around 10 to 30 watts will disperse the light more equally and are a good choice if you use a seedling tray and table. Linear grow light bulbs from about 10 watts will be good if you’re illuminating a small area. The ideal distance from grow lights to seedlings is 20cm or 8inch with a wide-beam angle grow light. This enables the seedlings enough space to grow, while the light is close enough so all light is used efficiently on the seedlings. If you'd like to use grow lights that are more powerful, such as 60W or more, you should install them at a much larger distance from the seedlings, e.g. 100cm or 40 inch, otherwise the seedlings will be overwhelmed and stressed by the amount of light. 

Operate the lights at regular hours

You may like to use a timer with these lights, so your lights turn on and off automatically. Consistency helps your plants to develop well. You can place the seedlings near the window and let your timer follow the natural pattern as much as possible. For example from 07:00 to 19:00 the lights are on. Don’t turn on your grow lights 24/7. During the day plants need to grow and develop. At night they need to rest and respire. 

Various notes

Good grow lights emit little heat, yet they can cause about one degree Celsius difference in ambient temperature directly under the light.

What else would you need think about? The quality of the seeds remains important, as well as the growth medium and nutrients, consistent watering, the right humidity and temperature. 

References:

Pennington, A. (2011). Apartment Gardening: Plants, Projects, and Recipes for Growing Food in Your Urban Home. Sasquatch Books.

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