Grow Lights Explained
Grow lights can be intimidating because there is a lot of uncommon terminologies that are used to describe and explain them. In this article, we will break down common grow light jargon so you can better understand the products you are shopping for and the different uses for them. Let's dive in and start with the different types of artificial light used in horticulture.
Different types of light are useful for different applications. There is PAR lighting (photosynthetically active light) to help plants grow which is different from photoperiod lighting which is used to control a plant's growth stage, and also different from supplemental lighting which compensates for reduced amounts of natural light.
Understanding photoperiod sensitivity, photosynthetic light vs supplemental light, and how light is measured is important to really understand horticultural lighting. You may want to follow those links and check out those respective articles before or after reading this article. Our greenhouse lighting knowledge base will definitely give you a comprehensive understanding in addition to the information in this article.
Grow Lights for Short-Day Plants
Short-day plants that thrive in ample light and will begin flowering when exposed to a threshold level of red light. Naturally, this is a cue that days are shortening and dusk is coming sooner, which tells the plant it is time to flower. 70 watts per meter PAR (photosynthetically active radiation) minimum should be maintained 18-24 hours a day to keep short-day plants in a vegetative state. Dropping light exposure to 12 hours of light and 12 hours of dark will trigger budding so lighting control is vital to successful greenhouse cultivation of short-day plants.
Light Bulb Color Temperature
Types of Artificial Lighting
|Type of Light||PAR Lighting||Photoperiod Control||Supplemental Lighting||Germination|
|Fluorescent tube lighting (T5)||X|
|Incandescent bulbs (Halogen lamps)||*||*|
|Compact fluorescent (CFL) bulbs||X|
|High-intensity discharge (HID) lamps||X||X||X|
|Light-emitting diodes (LEDs)||X||X||X|
Fluorescent Grow Lights
T5 Fluorescent Grow Lights
Fluorescent Grow Light Ballasts
Compact Fluorescent Grow Lights
Incandescent Bulbs and Halogen Lamps
Incandescent bulbs are commonly used for photoperiod control including cyclic lighting. Their lifespan will not be reduced by being turned on and off frequently or reduce the lifespan of the ballast. Incandescent bulbs are inexpensive, but not energy efficient. They emit a broad range of wavelengths and create a lot of heat. Incandescent bulbs are very familiar light bulbs that are used in homes. Halogen lamps are a type of incandescent bulb that has a small amount of a halogen gas such as iodine or bromine inside the bulb. Halogen lamps are more efficient than a standard incandescent bulb but are less efficient than HID bulbs.
LED Grow Lights
Light-emitting diodes (LEDs) are a newer lighting technology that has high efficiency and a long lifespan. LEDs come in a variety of light wavelengths and intensities that can target particular light color preferences. LEDs are effective in controlling photoperiod. LEDs with a low ratio of red to far-red light wavelengths promoted stem elongation in many species of plants. LEDs can be expensive but are a good replacement for incandescent bulbs since they can be purchased in spectrums and intensities of photosynthetically active light.
LED Light Viewing Angle
LED Grow Light Color Settings
High-Intensity Discharge Lamps (HID)
High-intensity discharge (HID) lamps include high-pressure sodium (HPS) and metal halide (MH) lamps. HID lamps may be used to provide photoperiod control by suspending them over the plant canopy, mounting to a boom, or using them with an oscillating reflector. HID lamps emit photosynthetically active light and are also used for supplemental lighting on short winter days and cloudy days. High-pressure sodium (HPS) lamps and metal-halide (MH) lamps are two popular types of high-intensity discharge (HID) lamps used in horticulture.
HPS lamp wavelength spikes at 632 nm, 605 nm, 589 nm, and 568 nm light wavelengths. MH lamp wavelength spikes at 674 nm, 630 nm, 583 nm, 564 nm, 540 nm, 497 nm, and 422 nm. Short-day plants respond better to HPS lamps, or a combination of HPS and MH lamps than to MH lamps alone. HID lamps produce a lot of heat, so it is important to have very good ventilation when they are used. HID lamps should have about two feet of space above the crop canopy to avoid burning the plants.
High-Pressure Sodium Lamps (HPS)
Metal Halide Lamps (MH)
Ceramic Metal Halide Lamps (CMH)
Mercury Vapor Lamps
HID Grow Light Ballasts
HID Grow Light Reflectors
Horticultural Lighting Problems
Greenhouse Grow Lights
Grow lights can be hung inside greenhouses to ensure that plants receive consistent levels of light throughout the year. Lighting may also be utilized to control plant growth cycles and is especially important to control when cultivating short-day plants. If natural light is too intense, shades and mesh screens can be used to add protection. Blackout shades or shutters ensure that light pollution does not damage crops that are very sensitive to the timing of light exposure.