General Lighting Information
High Intensity Discharge lighting, or HID lighting is a special type of lighting that is much more intense and brighter than other types of lighting available on the market today. An HID lighting system consists of a ballast, reflector or hood, socket and a bulb (grow lamp). The ballast acts as an engine, converting and driving energy to illuminate the bulb. HID bulb options include High Pressure Sodium (HPS), Metal Halide (MH), Mercury Vapor and Low Pressure Sodium. The two that are used for plant growth are High Pressure Sodium (HPS) and Metal Halide (MH).
Color Rendering Index (CRI), Color Temperature (K), and Lumens
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 of an ideal or natural light source. Incandescent light is assumed to have a CRI of around 100 so it will render all colors correctly. MH has a CRI of about 70, so only 70% of colors render correctly and HPS has a CRI of 22 with only 22% of colors rendering correctly.
Color Temperature is not referring to how hot the bulb is. Color temperature is the relative whiteness of a piece of tungsten steel heated to that temperature in degrees Kelvin. HPS has a color temperature of 2700K which is a warm or red color. MH has a color temperature of 6500K which is a cool or blue color. Note that the CRI readings of two different sources can only be compared if their color temperature is equal. You cannot compare the CRI of HPS (CRI of 22) versus MH (CRI of 70) because the color temperatures are different (2700K vs. 6500K).
Lumen is the measure of light output. One Lumen is 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. In the past, lumens have been the benchmark of a bulbs ability to grow plants, meaning the brighter the lamp the better the plant. However, recent studies have shown that a bulb with a better and broader color spectrum will produce more plant growth than a lamp with high lumen output.
Metal Halide and High Pressure Sodium Bulbs
Metal Halide bulbs put out a blue/green spectrum, which is ideal for plants in the vegetative (grow) stage and any leafy green crops. High Pressure Sodium (HPS) bulbs put out a yellow/orange/red spectrum, which is ideal for plants in the flowering (bloom) stage. When there is a need to supplement natural sunlight, growers will use HPS bulbs. For the most part, growers use Metal Halide bulbs for the vegetative stage and HPS for the flowering stage.
A conversion bulb is made to operate on the opposite ballast that it was designed for. Example, a 1000 watt Metal Halide conversion bulb will run on an HPS ballast. Conversion bulbs allow growers more flexibility when purchasing ballasts, bulbs, and setting up grow rooms for different types of plants or growth stages.
Fluorescent lighting is great for seedlings, cuttings and plants with low light-level requirements. Recent advances in fluorescent lighting technology have now provided more options for horticulturists. T5 fluorescent lighting is the newest in fluorescent plant lighting. T5 bulbs have high light output and low heat and energy consumption making them ideal to grow a broader array of plants than before. Due to the minimal heat output T5 bulbs can be placed 6”-8” above the plant canopy, maximizing photosynthesis. They also have an ideal spectrum for plant growth. Photosynthesis rates peak at 435nm and 680 nm. A 6500K T5 bulb has a spectral distribution with relative peaks at 435 nm and 615 nm. This means that very little light is wasted or unused by the plant. Note, it is recommended to use HID lighting for any plant over 3’ tall.
Magnetic and Digital Ballasts
The biggest difference between magnetic ballasts and digital ballasts is the frequency output to the bulb and the energy conversion of electricity to usable light. Magnetic ballasts produce a frequency of 60Hz. The frequency in digital ballasts varies from manufacturer to manufacturer, but it can be up to 400 times that of a magnetic ballast. Magnetic ballasts are heavier than digital ballasts, and produce more heat than digital ballasts, therefore making the digital ballasts more energy efficient than a magnetic. Note, that using a digital ballast will not save you money on your electric bill though. While digital ballasts are more efficient at converting electricity into usable light, your bill is not based on efficiency but kilowatt-hours. A 1000 watt digital ballast will cost you just as much to run as a 1000 watt magnetic ballast.
An average lighting system will add approximately $8-$20 to your electricity cost, per month, but can be as much as $100 more per lamp, per month. The exact amount will depend on the wattage per bulb, how many bulbs, and how long you run each one. To calculate the cost you multiply the bulb wattage by the number of hours of operation and divide by 1000. This will give you the number of kilowatt-hours used. Then find out the cost per kilowatt-hour in your area, generally located on your monthly bill. Now, multiply the number of kilowatt-hours used by the cost per kilowatt-hour and it will give you the cost of running your lighting equipment.
Voltage for HID and Fluorescent Lighting
HID systems are available in 120v, 208v, 240v, 277v, and 480v – all at 60Hz. Fluorescent lighting varies, but most are available from 100v to 277v and at 50Hz or 60Hz. The standard voltage used by most growers is 120v and 240v. 120v plugs into a standard wall outlet, and 240v plugs into the same type of outlet used for common household clothes dryers. The benefit of using 240v is that it pulls half the amount of amps as the same unit running on 120v, which is great when you are limited on amperage at your breaker. Using 240v will not save you money on your electric bill compared to 120v, but it will draw less current and run a little cooler than a 120v. Always contact a licensed electrician if you require special voltage outlets in your grow room. Never exceed more than 75% of your total fuse/breaker amps. (Example: don’t use more than 15 amps on a 20 amp circuit).
Most manufacturers rate their bulbs in “Average Life Hours” and usually claim 10,000 to 24,000 hours. This rating however is based on when the bulb will completely fail to turn on, and not when there will be a loss in intensity or color. HID lamps will lose both intensity and color through normal use, which is generally ok if you are lighting a warehouse, but when it comes to your prized plants these losses can mean wasted electricity and smaller yields. Experienced growers recommend replacing your bulbs after two harvests. You will generally notice that yields will start to diminish on the third harvest if you haven’t replaced your bulbs.
Daily Run Time
As a general rule, you will run your lights for 18-24 hours a day in the vegetative stage and 12 hours a day in your flowering stage. If you have natural sunlight available to your garden, and your lights are only supplemental, this may change the run time for your lights.
Hanging your Lights
This will mostly depend on the wattage of your bulb. The higher the wattage, the further away the bulb needs to be from the canopy due to heat issues. HID lighting will obviously need to be further away than a fluorescent light due to the same issue of heat. When hanging your light fixtures, you need to take into consideration the type of plant you will grow and how tall it will get. The light needs to be as close as you can have it without burning the plant. An easy test can be done with the back of your hand, if it is uncomfortable for the back of your hand it will be uncomfortable for the plant. Do some research on the type of plant you will be growing to determine how much or how little light they require. With fast growing plants, you may need to adjust the hanging height constantly as the plant grows toward the light. There are many types of hanging fixtures that will help with adjusting the height of your lights.
The size of your garden area will determine how many lights, and how many watts each, that you will need. Assuming there is no natural light, a 1000 watt light will cover a 4’x4’ area with proper light intensity. A 600 watt light will cover a 3’x3’ area, a 400 watt light will cover 2’x2’ to 3’x3’, and a 250 watt light will cover 2’x2’. These sized areas would be considered the “Ideal Growing” areas. The bulbs will light-up larger areas, but plants placed outside the Ideal Growing area will stretch and bend toward the light making them “stringy” or “lanky”. Keep your area coverage in mind, and remember that the best results occur when coverage areas overlap. There are many light meters that you can also use to test the intensity of light from any given location in your garden room.
Cleaning Your Reflector
Warm water and mild dish soap are the best to clean and maintain the highly reflective finish of your reflector. Avoid bleach, ammonia and other harsh or abrasive cleaners.
The internal components of ballasts are designed to send the correct voltage and current for the rated lamp. You cannot run a 1000 watt bulb on a 400 watt ballast. Mixing bulbs and ballasts will result in premature failure and will void the manufacturer’s warranty. Plan out the area that you want your grow room to be in prior to making your lighting purchase. It is easier to grow into a fixture than out of one. Also, manufacturers do not state the gloves are required to handle HID bulbs, but it is recommended.