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HID Lighting Introduction Modern bulbs are an attempt to re-create natural daylight in intensity and sometimes exceed it. It is the most important element of the grow room and is used by the plant to create energy by photo-synthesing to grow and develop. The plant does this by using the light energy from the sun, (or lamps) to react with the carbohydrates and water in the plant to produce energy and oxygen. You can almost never have too much light, unless then you are deficient in CO2 or some other limiting factor, in which case it’s pointless. The light supplied has to contain the correct spectrum in the right quantities, this is why incandescent (i.e. normal household) bulbs aren't of any use. Plants only seem to use the blue and the red ends of the spectrum. Blue is more important in the rooting/growth stage and red becomes more important when flowering. (At the end of the season) HID (High Intensity Discharge) High Intensity Discharge (HID) lights are the most efficient source of light a grower can use. These lamps produce five times as much light energy per watt of electrical energy than any incandescent lights and will last much longer. Bulbs range in sized from 100 to 1000 watts. HID lamps consist of a bulb, normally in a reflector, which is plugged into the mains electricity supply via a ballast. This ballast must be matched to the particular bulb for proper operation, e.g. A Metal Halide ballast cannot run a High Pressure Sodium bulb. (Unless you’re using a conversion bulb. MH conversion bulbs produce halide light and are designed for HPS fixtures. ). All HID lamps produce quite a large mount of heat, which must be vented out of the grow room. There are now 'cooling reflectors' available to take the hot air generated by the lamp out of the room via a small separate vent. The main drawbacks to HID lighting systems is that they put out intense heat, which subsequently causes plants to dry out faster, and the fact that they are incapable of providing the entire natural spectrum. HID lights come as close to natural light as human technology can take us, but natural sunlight is still more full and vibrant. There are two types of HID lamps to be aware of, Metal Halides and High Pressure Sodium’s. Both have a lifetime of about 12 to 18 months before they should be replaced. MH (Metal Halide) Metal halides have the more balanced spectrum. The light they give out has a significant amount of light from the bluer end of the spectrum, which the plant uses to grow vegetatively. It produces plants with a small internodal length, with large leaves and thick stems. It produces the most natural looking plants. It simulates the light from the beginning of the year and is good for plants before they're switched into flowering mode. They're normally slightly more expensive than HPS. Recently, there have been 'enhanced spectrum' MH bulbs produced which also give off a significant amount of red light. Conversion bulbs are also available which plug into HPS ballasts which are actually MH bulbs. Useful for changing the light balance without changing the ballasts also. In the event of a power failure, they need about 20 minutes before restating. They may restart earlier but it shortens the life of the bulb quite dramatically to try and start a hot bulb. HPS (High Pressure Sodium) HPS bulbs are the most common HID to use, especially during flowering, giving off characteristic reddish light. The red in the light spectrum encourages good flower/ fruit growth. It is possible to use HPS during vegetative growth, but only for a week or two. Older plants start to look a little unnatural and 'lanky', with large internodal length and brittle stems. For this reason conversion bulbs, or enhanced spectrum bulbs are needed, or even better, a Metal Halide. HPS bulbs can be re-started after about 3 minutes if powered down. How Much HID HPS or MH Light? Use 30 watts (normal) to 60 watts (with CO2) for each square foot of growing space or (350watt - 600watt per square meter). How Much CFL Fluorescent Light? Use 12.5 watts (normal) to 25 watts (with CO2) for each square foot of growing space or (150watt - 300watt per square meter). Fluorescents These are excellent for rooting cuttings, cupboard grows or supplemental lighting. The new range of high intensity lamps are especially useful in producing compact bushy plants up to a few inches tall.(e.g. Nebula, Lightwing or PL2 Propagation Unit). After reaching the height of about 10 to 12cm they'll start to get weak due to the poor penetration of a florescent. They have the advantage of being very cheap and easy to obtain. LPS (Low Pressure Sodium) Often mistaken for HPS. Also give off a red light. No good for growing, unless stunting cuttings. Halogen/ Incandescent Cheap and easy to obtain but give off too much heat in the wrong spectrum. Not used. Making the most of your lights Timers Keeping regular lights on/off ratio and sticking to it is very important. If the lights are inadvertently switched on within the dark cycle it can stress out the plants and produce strange results. The shortening of the days simulates autumn and brings many plants into flowering mode. Some varieties of plants are more photosensitive than others but all require a stable light regime. A good quality timer is essential. For bulbs care must be taken to use a timer that is rated for an inductive load equal to the light wattage. Light Contactors and Timer Relays A low cost solution to the problem of timer failure. The Lighsafe and Maxibright Contactor/ Timer Relays plug into your existing timer to protect against the inductive loads generated by the electrical discharge of Horticultural Lighting. A Contactor unit divert the electrical load from a timer to a heavy-duty relay or contactor. As a guide match the switching load to the correct Contactor unit, for example 2 x 1000w Sodium ballast = 10Amps running current (switching load) so a 10Amp rated contactor unit should be selected. Reflectors A good reflector is very important, there are many varieties and all help to keep the light where it’s needed. Air-cooled reflectors are also available. Walls should be painted or covered white. White is a better reflective than silver foil. Even better is Black & White plastic or Mylar. Both are easy to wipe down in between crops and will benefit your crop by minimising wasted light energy. Care All HID bulbs should be handled with care, using a cloth or towel. Any oil from your fingers can crack a bulb when it gets hot. Electricity Costs; 1) Multiply total kilo-wattage of your lights by hours switched on. (Gives Kilowatt Hours) e.g. (1 x 400w Ballast) 0.4 KW x 12 Hours = 4.8 = 4.8 Kw 2) Multiply this number by your price per unit on your bill. (A 'unit' is a Kw Hour) e.g. 4.8 Kw x £0.10 = £0.48 This gives the price PER DAY of running the bulbs. Light Movers These devices distribute the available light more evenly among the growing area. It stops the plants at the edge from stretching. It is especially useful if using a combination of HPS and MH light because it evens out the spectrum for the plants. There many varieties available. Conversion Lamps These are much used and eliminate the need to have separate ballasts for HPS and MH. The grower simply unscrews the old light and replaces it with the conversion bulb. Many still believe a true MH produces better results than the conversion bulb though. |
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