Hydroponic Grow Lights - Frequently Asked Questions

Q. What is HID Lighting?
A. HID Lighting stands for High Intensity Discharge Lighting, which is a special type of lighting that is much more intense than any other grow lamp available. It is perfect for growing vegetables, flowers and herbs year round, even if you do not have a greenhouse. The second most popular lighting for gardening is fluorescents. HID systems are TWICE as efficient as fluorescents. It would take twenty 40 watt, 4' fluorescents to put out as much light as one 400 watt halide system.

Q. Do I need special wiring for these lights?
A. No, all lamps are ready to plug into normal, 110 volt household outlets. Radiant Systems are multi-volt ready to allow for 220 volt conversion.

Q. Are there different kinds of HID lights?
A. Yes. The two types of HID lights available are METAL HALIDE and HIGH PRESSURE SODIUM. Metal Halide lamps come in 175, 250, 400, and 1000 watt sizes. High Pressure sodium systems come in 150, 250, 400 and 1000 watt sizes. Metal Halide lamps put out light that is high in the blue color spectrum. That is more like natural sunlight. In late 1994, 2 new metal halide lamps became available--the AGRO SUN Halides in 400 and 1000 watt sizes. These are halide bulbs designed specifically for agricultural use. They put out as much light as a "super output" halide, but they emit 15% more of the red/orange spectrum. This makes them even more like natural sunlight and an excellent all-around light choice. For growers who wish to experiment with color spectrum, halides can be a good choice. Each metal halide lamp kit--the 175, 250, 400 and 1000 watt systems--may be retrofitted with a CONVERSION BULB. This bulb works on a regular halide ballast, but emits sodium-type light. Because of this, the metal halide systems are perfect for those who wish to have a choice of both metal halide and high pressure lights, but want to use only one ballast. Also, metal halide lamps are a less expensive choice at the time of purchase.

High Pressure Sodium lamps put out light that is high in the red-orange-yellow color spectrum. The sodium bulbs have twice the life of the metal halide bulbs, needing to be replaced 1/2 as often. High Pressure Sodium lamps are the standard choice for greenhouse growers, since there is plenty of blue spectrum light available naturally in the greenhouse. A high pressure sodium bulb will emit more lumens of light for the wattage being used than a metal halide lamp. For example, a 400 watt halide system emits 40,000 lumens of light. A 400 watt sodium system emits 50,000 lumens of light. For the same amount of electricity, the 400 watt sodium lamp emits 25% more light than the 400 watt halide. Most folks who light with high pressure sodium systems use the agricultural bulbs, called "SON" or "SUPER AGRO". These are color corrected sodium bulbs that will operate with a regular sodium fixture. They emit 30% more of the blue color spectrum and emit 6% more light. Their benefits over typical sodium include healthier green growth and more sturdy, compact plant growth. The SUPER AGRO sodiums are available for the 400, 250 and 150 fixtures. There is no SUPER ARGRO available for the 1000 watt fixture at this time.

Q. Which light is better?
A. Different people have different objectives and we carry all lamps for that reason. Greenhouse growers typically will almost always choose high pressure sodium lights. Those who want to get "the most lamp for the money" go with the halides, as they cost less at initial purchase. The halides (especially the agricultural halides) are most pleasant to be around, so they are good choices for the in-home displays. Those more concerned with bulb replacement costs often choose the SUPER AGRO sodiums, as they offer excellent color spectrum with less frequent bulb changes. Many plants don't care what light is used, as long as they get enough light they are happy. So you can see, the choice is up to you, depending on your priorities and needs!

Q. How Often will I need to replace my bulbs?
A. Any Bulb will loose it's brightness very gradually as it is used. Halides of all types will need to be replaced at least yearly with continual use. Halide lamps will lose about 25% of their lumen output after a year of continual use. Agricultural (SUPER AGRO) Sodiums should be replaced about every 18 months; regular sodium every 2 years. Some folks like to replace even more often in order to continue getting optimum lumen output from their bulbs, but your plants will perform just fine following these replacement guidelines.

Q. Can I put 1000 watt bulb in my 400 watt system?
A. No. You must be very careful to only use the bulb appropriate for your system.

Q. How many hours should I keep my lights on in my garden?
A. That depends on what you are growing. Plants that produce fruits and flowers when they receive minimum hours of darkness are long day plants. A few examples of long day plants are coleus, bromeliads and gloxinia. These, and all other long day plants, will perform best with 16-18 hours of light and 6 hours of darkness. Occasional interruption of the dark hours due to entering the greenhouse or grow room and turning on lights, etc., will not adversely affect long day plants.

Day neutral plants are not affected by day length, as the category name implies. They flower or bear fruit due to physiological age or temperature. Although plants in this category do no have specific lighting requirements, some will show improved yields and performance with a longer, 15-18 hour, light "on" cycle and the corresponding 9-6 hours of darkness. Day neutral plants include tomatoes, chilies, eggplants, sweet peppers, zinnias, marigolds and roses, as well as the new day neutral strawberry varieties. Check the information listed on you seed packs or in the seed catalogs, or contact your country extension agent for information on optimum lighting hours for these plants.

Short day plants need 12 hours of night (darkness) to promote flowering. Any interruption of this dark period will result in uneven or delayed flowering/fruiting in these plants. A couple of examples of short day plants are poinsettias and chrysanthemums.

Some plants are not classified as strictly "short day", but will perform best with 12 to 14 hour days. Most lettuces, broccoli, cauliflower, snow peas, chard and other typical spring and fall crops fall into this category. Herbs will do just fine with shorter light hours, too.

For mixed gardens--when you are growing herbs, lettuce, broccoli, tomatoes and peppers, for example--we suggest that you try to hit a happy medium on your garden's light hours. 14 to 15 hours should be short enough to head up the broccoli and prevent lettuce from bolting, but long enough to keep those tomatoes coming on. Also, strategic placement of plants helps a lot. The plants with the highest light requirements should grow in the most intensely lit areas of the g