Lighting the Indoor Greenhouse

For the novice greenhouse gardener, the array of options for indoor greenhouse lighting available at your local greenhouse supply store can sometimes seem bewildering. This article aims to help you make the best choices for lighting your indoor greenhouse.

How Much Light Do I Need?

The first thing to consider is how much light your indoor greenhouse will need. This depends on two factors, the size of your greenhouse and the type of plants you are growing. Tall plants need more light to grow than small ones, and fruits and flowers need more light than herbs and ferns.Rule of thuimb is that if plants prefer to grow in the shade, they need less light than those preferring a sunny position.  For outdoor greenhouses, the general rule is 25 watts per square foot of garden space, but for lighting indoor greenhouses, many gardeners use double or triple that amount. It is impossible to give your plants too much light, so use as much as you can afford.

Types of Indoor Greenhouse Lighting

There are many different types of indoor greenhouse lighting, each of which has its own advantages and disadvantages.

HID stands for High Intensity Discharge and is the most energy efficient type of indoor greenhouse lighting available, but also the most expensive by far. HID lamps come in two varieties, Metal Halide (MH) or High Pressure Sodium (HPS). MH lamps produce light in the blue spectrum, which is best for green leafy plants. Flowers and fruit work better with HPS lamps, which emit a reddish-orange glow similar to that of a sodium streetlamp. Red spectrum light stimulates growth hormones which helps these types of plant to grow.

Fluorescent grow lights are less expensive than HID lights, but they are also bigger and bulkier. For this reason, they have traditionally had a bad reputation among greenhouse gardeners, though this is now changing thanks to the production of more efficient fluorescent lights with a higher output. Another advantage of this type of indoor greenhouse lighting is that it produces much less heat than HID lights.

Incandescent lights are the least expensive type of grow light, but the saying “you get what you pay for” very much applies here. They are only really any use for the very smallest table top herb garden, as they do not produce enough light to sustain most plants.

The newest type of indoor greenhouse light is the LCD grow lamp. They have rapidly gained in popularity due to their energy efficiency and lack of unwanted heat production, though tests have shown that they do not significantly outperform equivalent fluorescent lights.

The Importance of Darkness

Whatever type of indoor greenhouse lighting you choose, it is important to remember not to run it all the time. Plants need some darkness in order to grow properly. Depending on the type of plants you are growing, you should leave the grow lights off for between 6 and 12 hours each day.

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