Light is the initial energy source of nearly all of the food chains on the planet. When mankind first learned to harness the power of the sun to grow crops, civilization began and we haven’t looked back. We are now in a new era of agriculture, an era where gardens have become more advanced and technology is playing an ever-increasing role in our food production. Gardening indoors is the forefront of science and change in the gardening world. When we bring the garden indoors, we are saying we have the knowledge and ability to compete with nature.

Supplying your indoor garden with sufficient light is of the utmost importance. There are many ways to go about this depending on a variety of factors such as space and the types of plants being grown. There are also many ways we can improve upon the lighting we use to garden indoors. We can make our lighting more efficient to get the most out of the hard-earned dollars we spend on lighting gear and electricity for each crop.

Buying Bulbs

Buying the right bulb for both the growth and flowering stages of plant growth is essential. Each stage of plant development has different lighting requirements. Plants in the growth stage require 18 hours of uninterrupted light and six hours of darkness per day. They also grow best under bulbs labeled “cool” or “blue” or “grow.” These bulbs provide “blue” light in the range of 6,500 K. Using these bulbs during the grow phase will boost leafy growth while keeping plants dense and squat.

Plants in the flowering stage of plant growth will require 12 hours of uninterrupted light followed by 12 hours of uninterrupted darkness per day. Flowering plants grow best under bulbs labeled “warm” or “red” or “flower.” These bulbs provide light at the red end of the spectrum, which boosts flower and fruit production.

Wattage is also important when buying high intensity discharge (HID) bulbs. The wattage generally dictates the amount of area that can be lit and the number of fast-growing plants that can be successfully grown. A 400-W bulb can light a 3-ft. by 3-ft. space, a 600-W bulb can light a 4-ft. by 4-ft. space and a 1,000-W bulb can light up a 5-ft. by 5-ft. space.

When considering bulb options before purchase, be sure to find out the PAR (photosynthetically active radiation) watts of the bulb. The PAR watts of any given bulb gives you the actual amount of light energy your plant will be able to absorb from that bulb. This level will diminish as the bulb gets used and ages. For instance, if you buy a 1,000-W high pressure sodium (HPS) bulb from an industrial lighting supplier, it may only have 75 PAR watts for that bulb. A 1,000-W HPS from a hydroponics retailer would easily provide four or five times the PAR watts than the discount industrial bulb.

Replacing Bulbs

Always replace your bulbs after nine to 12 months of continuous use. Those PAR watts drop fast. We may not notice the difference, but your plants definitely can and plants under new bulbs always grow better than under older bulbs.

When replacing your bulbs, there are some tricks that can make the process easier. Almost all high-quality grow bulbs have a one-year manufacturer’s warranty. Most retailers will etch the date into the base of the bulb at the time of purchase. If they don’t, you should. Adding a bit of petroleum jelly to the threads on the base of your bulb will make it much easier to remove when the time comes. Also, never handle your bulbs with you bare hands if you can avoid it. The oils on your hands will actually burn into the surface of your bulb, slightly diminishing the lumen output.

Never get liquid on your bulbs while they are on. I have heard countless stories of individuals accidentally misting their bulb when foliar feeding their plants only to have the bulb explode on contact with the cool water. Not only is this mistake costly, it is also dangerous, as glass shards will become shrapnel. HID bulbs with damage to the outermost glass must not be used. This layer of glass filters out the harmful UVA and UVB rays emitted by the light and can cause sunburn and blindness.

Making the Most of Your Lights

There are some tricks we can use to help us harness our lights to the fullest potential. Light movers are an efficient way of limiting the number of lights you need in your grow space. This reduces the cost of replacement bulbs and electricity, while helping to keep the room temperature down. Light movers physically transport the lamp and bulb, spreading the light out. The two most common types are either fixed to a rail that provides lateral back and forth motion to the lamp, and the type that spin your lamp in a circular rotation.

Reflectors also play a major role in lighting your growroom. Reflectors reflect the light from your bulb in an efficient way back to your plants. For instance, a bulb hanging horizontally over your plant canopy would have half its light wasted, as the light would shine 360° around the bulb. A horizontal reflector reflects much of that light and focuses it back on your plants. Horizontal reflectors are ideal for concentrating the light on a smaller area, while vertical reflectors are great for evenly spreading the light over a larger surface.

Using reflective material can also help trap and use your light in the growroom, while keeping light out of the room during the dark hours. There are various types of reflective materials available. The most common is mirrored Mylar and black and white plastic. I personally prefer the black and white plastic, as it does not create hot spots and the black side can absorb light, preventing unwanted light from getting into your growroom during the dark hours.

Light distance from the canopy can also be a factor as to whether your plants are getting enough light or not. If the light is too close, the plants can get burned, dry up quickly, and insect growth can be enhanced. If the light is too far from the plants, growth will be stunted, plants will become weak and stretched as they grow closer to the light, and fruit production will be pitiful.

What’s the Correct Distance?

That depends on the type of lights you are using and the type of plants you are growing. High-output fluorescents and LED lights are relatively cool and the lights can be as close as 6 in. away from the leaf canopy. HID lights are much hotter and should be placed at least 12 in. away from the leaf top to prevent burning. Air-cooled reflectors do offer some leeway, as the heat from the bulb is continuously being removed by fans. Once you find that sweet spot where the bulbs are as close as they can safely be to the plants, hang a string measuring that distance to your reflector. When you check on your plants, the string will tell you whether or not you need to raise the reflector.

Lighting in the growroom is a tricky business, but the proper selection, use, maintenance and replacement of your bulbs will ensure success in the garden.