One of the most important decisions you will make as you start delving deeper you’re your indoor garden is the lighting. You’ll need to expand your knowledge of the light needs of plants, what types of lighting options work in what situations and what type of lighting options are out there.
What are grow lights?
Simply put, grow lights are electric lamps used as a sunlight substitute for indoor plant growth. Grow lights are designed to emit an “electromagnetic spectrum” that makes photosynthesis (the process of converting carbon dioxide into sugar using sunlight), and thereby plant growth (and life itself!!), possible.
Grow lights consist of the bulb, the socket assembly, the cord, ballast and a reflector. Light lifts and light movers can help to make your set up easier to use.
When it comes to grow lights there are a wide variety to choose from: LEDs, incandescents, fluorescents, high pressure sodium, metal halide and, of course, who could forget the high-intensity discharge lamp (HID).
How much and what kind of light do indoor plants need?
There is no reason to get too technical here but there are a few things worth keeping in mind.
1. The electromagnetic spectrum emitted by your grow light needs to mimic that of natural daylight.
2. Plants require different light spectrums at different points in the growth cycle. In the early stages plants prefer the blue spectrum of light. Later on, during the flowering stage, they need the red–orange-yellow spectrums.
3. To get the optimum lighting for your plants you’ll need to have a general idea of the light needs of your plants and will need to imitate the lighting present in that plants natural environment. Remember, the bigger the plant the more light it will need. 12 hours a day for most plants is a good rule of thumb.
4. Most vegetables grow best in full sunlight so if you’re growing veggies indoors and away from a window they will need as much light as possible. On the other hand, many foliage plants such as philodendrons need much less light.
5. Light looses its effectiveness the further it is away from the bulb. That means that you will have to keep the plants within a certain distance from the light – this is especially true with fluorescent lights.
6. Grow lights can be bought by spectrum color but full spectrum bulbs are quite common these days and can make your life much easier.
7. All plants need both light and dark periods. To make your life easier, you’ll want to purchase a timer to switch your grow lights on and off based on the needs of your plants.
Indoor Grow Light Options – When and Why?
So what kinds of lights are best for what kind of plants and at what stages of growth? Well, I look at it as a three-stage process of sorts.
Indoor gardeners tend to use fluorescents for clones and seedlings. Once your plants get to the vegetative stage you can continue using the fluorescents but their effectiveness will diminish so you’ll need more bulbs to get healthy growth.
The nice thing about fluorescent bulbs is that they will not burn the plants so you can put your seedlings as close as you want. My mother has her fluorescent set up only 2 inches above her plants. Whatever you do, don’t put the plants more than a foot away from the bulbs as the effectiveness diminishes to a point of being worthless.
For your seedlings, try to find bulbs that are labeled “cool” or “cool white” as well as “high output” or “plus”. These combinations will give you a lot more that blue light in the spectrum.
You’ll find that metal halide lamps are best for the vegetative stage of growth. Metal halide lamps have a slightly bluish light that is more similar to sunlight. It’s this blue light that keeps plants somewhat stocky and helps to develop the stems and leaves. An absence of the good blue stuff will make the plants stringy, viney and unhealthy.
Metal halide bulbs also produce UV radiation which is known to increase the potency of herbs and may increase the nutrient level in some vegetables and plants. Keep in mind that Metal halide, unlike the fluorescents, WILL burn your plants. Therefore, be sure to keep your plants 12-18 inches away from the bulbs at least.
Obviously, this will depend on what strength of lamp you are using. You’ll have to keep a 1000 watt lamp about two feet away from the plants while a 250 watt bulb can be just a foot distant. Also, be sure that you have good air circulation and temperature control so your plants don’t overheat. Use metal halide lights until your plants are 24-36 inches tall.
Although you can use metal halide for flowering, budding and fruit production on your indoor plants they generally require much more light at this stage than in the vegetative stage. They also require a different kind of light, the red-orange-yellow light of late summer and autumn. Therefore, high pressure sodium lights (HPS) are more commonly used in this stage. Again, use the 12-18 inches rule for your plant-lamp bulb distance. HPS bulbs will burn your plants if too close.
Safety, Efficiency and Design
As you’re putting this all together keep in mind that the heat your bulbs produce, the amount of electricity your bulbs use and how you safely mix the water needs of your plants with the electricity needs of your bulbs are all going to impact the design of your indoor garden. So, ask yourself a few questions:
- Are you going to dedicate an entire room to your indoor garden or will it be spread out between several rooms?
- What are you growing and at what stage? Will this be a vegetable garden? Will you be growing from seed thru fruiting setting or will you be purchasing starts?
- Are you growing low-light plants or plants with a lot of light needs?
- Finally, what kind of exhaust fan and air circulation system will you be using and what size will it be?
Want to learn more about grow lights?
Here’s a handy-dandy little fan calculator here.
Clean Air Gardening and Home Harvest have a good list of different types of grow lights with pictures.
Jim O’Donnell gardens in the mountains of northern New Mexico. A certified permaculture designer and ecological restoration specialist, Jim’s first book Notes for the Aurora Society was published in 2009.