Hydroponic Grow Lights

Most plants grown in a hydroponic setting require light, lots of it.

They photosynthesize to manufacture their own nutrients. They need warmth to keep biochemical reactions going, and progress at the right rate. They determine many processes by the amount of light present, speeding some up and shutting down others.

During photosynthesis plants take in carbon dioxide and water to produce glucose and oxygen. The glucose is used as an internal energy source and much of the oxygen is discharged. But the color and intensity level of the light they receive plays a big role in how they achieve that.

The fact that leaves are generally green and/or yellow shows that those colors are being reflected. The other constituents of white light (which is a mixture of many wavelengths) are mostly absorbed. But some are absorbed more efficiently than others at different growth stages. Wavelengths in the range of the spectrum we perceive as red are more commonly employed during growth phases. Blue is absorbed more to produce flowering or fruiting.

Since few hydroponic gardens are simply left out in the sun to take their chances, a grow lights scheme is required to assist them in all those activities.

Plants sited near an open window or grown outdoors largely self-regulate the wavelengths they absorb, where the whole spectrum is abundant. But those that live indoors can only take up what is available at the time. That makes it very important to ensure that they have all the light they need, both in terms of intensity and wavelength.

Indoor grow lights are typically less intense (provide less overall energy than natural light) and therefore plants may need to be supplemented with natural light. Or, it may be appropriate to use special grow lights to provide the total amount of light energy required to provide warmth, photosynthesis and other useful tasks. The combination will vary from one climate to another.

Indoor grow lights come in a variety of types, prices and wavelengths, some better for plants than others.

Incandescent grow lights provide a lot of heat. They're fairly inefficient at using electricity for that reason, but, they produce strongly at the red end and weakly in the blue range.

Many fluorescent grow lights, by contrast, tend to produce greenish light. They're filled with mercury and the inner coatings that produce light in the visible range may be better or worse at producing a white-approximating spectrum. They are, though, a much cheaper to use in the long run.

A relatively inexpensive setup can be achieved with a combination of incandescents and fluorescent grow lights. A 30-watt incandescent with a 100-watt equivalent fluorescent provides a good balance of wavelengths. Fluorescent grow lights use far less electricity so the wattages can't be compared.

While they cost more, metal halide and sodium lamps make very good grow lights for hydroponic gardens. Metal halide lamps produce very well in the blue range and sodium lamps provide more reddish light. Unfortuately, the bulbs can't be switched between fixtures so it's necessary to buy a housing appropriate to each type.

Some newer LED grow lights will produce a very broad spectrum and some can be adjusted to favor one wavelength range. However, they're expensive and many won't produce the same output as any of the other types although the technology is rapidly evolving.

Plants vary in the intensity of light they require, as well. Ensure that average light plants receive at least 1,000 foot-candles. Others will need 2,000 foot-candles (about 20 watts per square foot) or more. A good light meter will tell you how much light is being given off, or you can sometimes find the rating listed on packaging or advertisements.

Most grow lights should be placed about a foot away from the plant to provide the proper intensity. The figure will vary considerably, though, hinging on whether incandescents, fluorescents or another source is used.

Plants that receive sunshine need from 8-10 hours light per day. If all artificial light is used, the number rises to between 12-14 hours per day. For some plants and lighting schemes 16-18 hours per day may be needed. The specific number depends heavily on the species of plant.