High Intensity Discharge (HID) is an excellent lighting choice for the indoor gardener. We use a Hydrofarm Super Grow Wing System which consists of a 15 pound lamp fixture attached to a 30 pound ballast with an 8 foot long power cord. The lamp fixture is suspended from the ceiling by two metal chains attached to hooks screwed into the ceiling rafters. The bottom of the lamp fixture is 36 inches above the wire rack table top. Trays filled with plants are then placed on the table top surface.
Over the winter months, you can grow healthy indoor plants that flower freely. The secret to success is using artificial lighting. The best artificial indoor light source is the Metal Halide (MH) lamp. We have used both Sunmaster Warm Deluxe Metal Halide and GE Multi-Vapor Metal Halide #MVR400/U 400 watt lamps with identical results. Both lamps screw into a M59 bulb socket. The Sunmaster lamp looks long and thin, while the GE lamp looks like a super giant sized light bulb.
We purchased our fixtures and bulbs from CropKing. We purchased 400 Watt MH-HID replacement bulbs every year.
Metal Halide lamps produce light by discharging an electric arc through a mixture of gases and gaseous metals. Plants require a specific intensity, quality, and duration of light to remain happy, healthy, and set bloom.
People have been growing plants in agriculture for the better part of 20,000 years. Early on, light intensity was recognized as an important factor. So, you'd think that after 20,000 years, civilization would have created an easy to use system of quantifing light intensity. You would think that, but you would be mistaken.
Typically, growing conditions for outdoor plants are primatively classified as "sun" or "shade". Indoor plants are treated little better, classified as "high", "medium", and "low" light. Not a very quantative system.
On the otherhand, lamp intensity was measured in "footcandles". That is, the amount of light produced by the flame of one candle measured at a distance of one foot (one footcandle of light falling evenly across one square foot is called a "lumen"). Footcandles of light can be approximated by using a photographic light meter.
| Below HID Lamp |
Exposure Value (EV) Reading |
Footcandles Of Light |
| 7.5" | EV 9 | 3200 FC |
| 15.5" | EV 8 | 1600 FC |
| 26" | EV 7 | 800 FC |
| Actual Daylight Measurements |
Exposure Value (EV) Reading |
Footcandles (FC) Of Light |
| Full Sun | EV 10.0 | 9200 FC |
| Part Sun | EV 8.0 | 1500 FC |
| Shade | EV 6.0 | 400 FC |
| Deep Shade | EV 5.0 | 200 FC |
| Actual Daylight Measurements - readings taken 17 February 2002 at 3PM CST. Sunny day with light wispy clouds, air temperature mid 40s F. Full Sun - reading taken in open area without any tree canopy or nearby trees. Part Sun - reading taken in forest with decidious tree canopy. Shade - reading taken in the shadow of a pine tree, but otherwise in an open area with no tree canopy overhead. Deep Shade - reading taken in the shadow of a pine tree and directly beneath a full pine tree canopy. | ||
We measured the light intensity from a new 400 watt Sunmaster Warm Deluxe Metal Halide grow lamp. Readings were taken at 12 inches and at 24 inches below the lamp fixture. We took EV readings using a Gossen Luna-Star F2 photographic light meter and FC readings using an Extech meter.
We found that a new 400 watt Sunmaster Warm Deluxe Metal Halide grow lamp produced 3000 footcandles at 12 inches and 1500 footcandles at 24 inches below the lamp fixture (our older lamp produced slightly lower readings). Replace your HID lamps about every year (3,000 hours), rather than waiting until it burns out (20,000 life hours on average).
We also measured the light produced from a one year old 400 watt High Pressure Sodium (HPS) lamp. The lamp was encased within an opaque glass fixture. We found that the High Pressure Sodium produced only 220 footcandles at 12 inches and 110 footcandles at 24 inches below the lamp fixture. No doubt, the opaque glass had greatly reduced the amount of transmitted light. We have since discarded this old style HPS lamp fixture.
|
Exposure Value (EV) to Footcandles (FC) | ||
| Exposure Value (EV) Reading |
Footcandles Of Light (FC) |
Daylight Equivalent |
| EV 10 | 6400 FC | Full Sun |
| EV 9 | 3200 FC | Part Sun |
| EV 8 | 1600 FC | Bright Overcast |
| EV 7 | 800 FC | Open Shade |
| EV 6 | 400 FC | Shade |
| EV 5 | 200 FC | Deep Shade |
| EV 4 | 100 FC | Twilight |
Properly measuring the light intensity produced by the lamp is a highly debated issue. These archaic measurement units of footcandles and lumens have several flaws. First, one footcandle, and one lumen, are very tiny units of light compared with direct overhead sunshine. Second, a footcandle is a measurement of visable light as seen by the human eye, which is not necessarily a proper spectrum of light useable by a plant. A better measurement unit of light for indoor plant growers is a PAR (Photosynthetically Active Radiation) watt. Unfortunately, since photographic light meters do not measure PAR watts, the only convenient way for indoor gardeners to measure light is with footcandles.
Lamps refer to "warm" and "cool". "Warm" refers to a high production of the yellow - red spectrum component of light (this spectrum component induces blooming). "Cool" refers to a high production of the blue spectrum component of light (this spectrum component induces vegetative growth).
Spectrum of Daylight, 400-700nmHome back to the home page.
Spectrum Visable to the Human Eye, 492-586nm
Spectrum Useable to Plants, 400-492nm & 586-700nm
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