FAQ - Horticultural Lighting

General Lighting Questions

• What is HID Lighting?
• HID lighting stands for High Intensity Discharge, which is a special type of lighting that is much more intense (brighter) than other type of lighting available. An HID lighting system consists of a ballast, reflector, socket and lamp (light bulb). The ballast acts like the engine, converting and driving energy to illuminate the lamp. HID lighting options include High Pressure Sodium (HPS), Metal Halide (MH), Mercury Vapor and Low Pressure Sodium. The two typically used for plant growth are HPS and MH systems.
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• What is Color Rendering Index (CRI), Color Temperature (K) and Lumen?
• Color Rendering Index is a subjective measurement of how well a lamp source renders colors. A measurement of the degree of color-shift an object undergoes when illuminated by a light source when compared to a reference source of comparable color temperature. Incandescent light is assumed to have a CRI of around 100 so it will render all colors correctly. MH only has a CRI of about 70, so only 70% of colors will be rendered correctly. HPS has a CRI of 22.
• Color Temperature is not how hot the lamp is. Color temperature is the relative whiteness of a piece of tungsten steel heated to that temperature in degrees Kelvin. HPS has a warm (red) color temperature of around 2700K as compared to MH at 4200K, which has a cool (blue) color temperature.
• What is important to remember about these two terms is that CRI readings, of two sources, can only be compared if their color temperature is equal. You cannot compare the CRI of HPS (CRI=22) vs. Metal Halide (CRI=70) because the color temperatures are different (2200K vs. 4500K)
• Lumen is a measurement of light output. It refers to the amount of light emitted by one candle that falls on one square foot of surface located at a distance of one foot from the candle. Traditionally, lumens have been the benchmark of a lamps ability to grow plants; meaning the brighter the lamp the better the plant. However, studies have shown that a broader color spectrum lamp will perform much better than a lamp with high lumen output, especially when it comes to plant growth.
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• What is the difference between MH and HPS with regards to plant growth?
• MH lamps provide more of the blue/green spectrum, which is ideal for leafy crops, and/or plants that are in a vegetative (actively growing) stage. MH lamps provide a more natural appearance in color and are typically the choice for plants that have little to no natural light available. HPS lamps provide more yellow/orange/red spectrum, which is ideal for most plants that are actively fruiting and flowering. In addition, HPS lighting is the choice for growers looking to supplement natural sunlight. Ideally, the horticulturist will use MH to grow their plants and HPS to fruit and flower their plants.
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• What is the difference between HID and Fluorescent lighting with regards to plant growth?
• Traditionally, fluorescent lighting was used for seedlings, cuttings and plants with low light-level requirements and HID was used for established plants and plants with higher light-level requirements. Advances in fluorescent lighting technology, however, have provided more options for horticulturists. T5 fluorescent lighting is the latest in plant growth lighting. T5's high-light output combined with its low heat and energy consumption makes it an ideal light source to grow a broader array of plants.
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• What are the benefits of using T5 fluorescent lighting for plant growth?
• T5 lamps provide the ideal spectrum for plant growth. Photosynthesis rates peak at 435 nm and 680 nm. A 6500K T5 lamp has a spectral distribution with relative intensity peaks at 435 nm and 615 nm. This equates to very little wasted light energy in terms of plant growth. T5 lamps promote incredible health and vigor of seedlings and cuttings. Root development is superior relative to other lighting sources. While T5 lighting is excellent for starting seeds and cuttings, it's also able to produce enough light for full term growth. Because of their minimal heat output, T5 lamps can be placed 6" -8" above the plant canopy which maximizes photosynthetic response. Unlike conventional fluorescents, plants grown under T5 lamps do not have to be rotated to the center of the lamp. T5's slim diameter enables better photo-optic control of the emitted light, increasing efficiency in the form of even light distribution.
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• What are the major differences between HID ballasts and electronic ballasts?
• Frequency output to the lamp and energy conversion from electricity to usable light are the biggest differences between HID ballasts and electronic ballasts. HID ballasts produce a frequency of 60 Hz. Electronic ballasts vary from manufacturer to manufacturer, but the frequency produced can be 400x that of an HID ballast. HID ballasts produce more heat than electronic ballasts, thus making electronic ballasts more energy efficient. You will not, however, save money on your electric bill by using electronic ballasts. HID lighting has been available for 60+ years, while electronic ballast (especially 400 watt and higher) is a relatively new technology.
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• Are electronic ballasts more energy efficient?
• Electronic ballasts are more efficient at converting electricity into usable light. Since your power bill is based on kilowatt-hours and not efficiency, a 1000 watt electronic ballast will cost you about the same as a 1000 watt HID ballast to operate.
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• How much energy will my light use?
• An average lighting system will increase your electricity cost about $8 to $20 per month. The exact amount depends on the wattage of the system and the number of hours operated. To calculate your cost, multiply the bulb wattage X the number of hours of operation and divide by 1000. This figure is the number of kilowatt-hours of electricity used. (Example: a 400 watt lamp running for 18 hours will use 7.2 kilowatt-hours). Check your power bill for the cost of each kilowatt-hour. Then multiply the number of kilowatt-hours used by the cost of a kilowatt-hour (K/hr) to figure the cost to run your light for that many hours.
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• Do I need special wiring in my house for my lighting system?
• Lighting systems are available in a variety of voltages. The standard used by most gardeners is 120 volts / 60 Hz which plugs into a standard wall outlet. Other voltages may require special circuits and receptacles. Always contact a licensed electrician if the light you purchased has special voltage requirements and never exceed more than 75% of the rated ability of the fuse/breaker. (For example: use no more than 15 amps on a 20-amp circuit.)
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• What voltages are available for HID and Fluorescent lights?
• HID systems are available in 120 volt, 208 volt, 240 volt, 277 volt and 480 volt - All at 60 Hz. Fluorescent lighting varies, but most are available from 100 volt to 277 volt and 50 Hz or 60 Hz.