Grow light
A grow light is an electric light that can help plants grow. Grow lights either attempt to provide a light spectrum similar to that of the sun, or to provide a spectrum that is more tailored to the needs of the plants being cultivated. Outdoor conditions are mimicked with varying colour temperatures and spectral outputs from the grow light, as well as varying the intensity of the lamps. Depending on the type of plant being cultivated, the stage of cultivation, and the photoperiod required by the plants, specific ranges of spectrum, luminous efficacy and color temperature are desirable for use with specific plants and time periods.
Typical use
Grow lights are used for horticulture, indoor gardening, plant propagation and food production, including indoor hydroponics and aquatic plants. Although most grow lights are used on an industrial level, they can also be used in households.According to the inverse-square law, the intensity of light radiating from a point source that reaches a surface is inversely proportional to the square of the surface's distance from the source which is a serious hurdle for indoor growers, and many techniques are employed to use light as efficiently as possible. Reflectors are thus often used in the lights to maximize light efficiency. Plants or lights are moved as close together as possible so that they receive equal lighting and that all light coming from the lights falls on the plants rather than on the surrounding area.
A range of bulb types can be used as grow lights, such as incandescents, fluorescent lights, high-intensity discharge lamps, and light-emitting diodes. Today, the most widely used lights for professional use are HIDs and fluorescents. Indoor flower and vegetable growers typically use high-pressure sodium and metal halide HID lights, but fluorescents and LEDs are replacing metal halides due to their efficiency and economy.
Metal halide lights are regularly used for the vegetative phase of plant growth, as they emit larger amounts of blue and ultraviolet radiation. With the introduction of ceramic metal halide lighting and full-spectrum metal halide lighting, they are increasingly being utilized as an exclusive source of light for both vegetative and reproductive growth stages. Blue spectrum light may trigger a greater vegetative response in plants.
High-pressure sodium lights are also used as a single source of light throughout the vegetative and reproductive stages. As well, they may be used as an amendment to full-spectrum lighting during the reproductive stage. Red spectrum light may trigger a greater flowering response in plants. If high-pressure sodium lights are used for the vegetative phase, plants grow slightly more quickly, but will have longer internodes, and may be longer overall.
In recent years LED technology has been introduced into the grow light market. By designing an indoor grow light using diodes, specific wavelengths of light can be produced. NASA has tested LED grow lights for their high efficiency in growing food in space for extraterrestrial colonization. Findings showed that plants are affected by light in the red, green and blue parts of the visible light spectrum.
Common types by generation
Fourth generation: Light-emitting diodes (LEDs)
light is regarded as the fourth generation of light sources. LED lights produce the highest photosynthetically active radiation of any light.LED grow lights are usually composed of multiple individual light-emitting diodes in a casing with a heat sink and built-in fans. Most or all LEDs use AC/DC or DC/DC power supplies that provide constant direct current through the LEDs, regulating the amount of total power the LEDs can draw and preventing their failure.
Individual LEDs usually provide only a single narrow range of colors, and so different color LEDs are mixed in grow lights in proportions depending on the intended use. It is known from the study of photomorphogenesis that green, red, far-red and blue light spectra each have an effect on root formation, plant growth, and flowering, but there are not enough scientific studies or field-tested trials using LED grow lights to recommend specific color ratios for optimal plant growth under LED grow lights. It has been shown that many plants can grow normally if given both red and blue light. However, many studies indicate that red and blue light only provides the most cost efficient method of growth, plant growth is still better under light supplemented with green.
White LED grow lights provide a full spectrum of light designed to mimic natural light, providing plants a spectrum of red, blue and green. White light is rated on a spectrum in terms of color temperature where cooler lights produce more blue photons and warmer lights produce more red photons.
A large number of plant species have been assessed in greenhouse trials to make sure plants have higher quality in biomass and biochemical ingredients even higher or comparable with field conditions. Plant performance of mint, basil, lentil, lettuce, cabbage, parsley, and carrot were measured by assessing health and vigor of plants and success in promoting growth. Promotion of profuse flowering in select ornamentals including primula, marigold, and stock were also noticed.
In tests conducted by Philips Lighting to find an optimal light recipe for growing various vegetables in greenhouses, it was found that the following aspects of light affect both plant growth and plant development : light intensity, total light over time, light at which moment of the day, light/dark period per day, light quality, light direction and light distribution over the plants. However it's noted that in tests between tomatoes, mini cucumbers and bell peppers, the optimal light recipe was not the same for all plants, and varied depending on both the crop and the region, so currently they must optimize LED lighting in greenhouses based on trial and error. They've shown that LED light affects disease resistance, taste and nutritional levels, but as of 2014 they haven't found a practical way to use that information.
The diodes used in initial LED grow light designs were usually 1/3 watt to 1 watt in power. However, higher wattage diodes such as 3 watt and 5 watt diodes are now commonly used in LED grow lights. For highly compacted areas, COB chips between 10 watts and 100 watts can be used. Because of heat dissipation, these chips are often less efficient. Standard LED lighting usually has a power factor of at least 0.90, while good quality LED lights will be around 0.99.
To prevent leaf burn, LED grow lights should be kept between away from plants for lower wattage lamps up to away from plants for higher wattage lamps.
Historically, LED lighting was very expensive, but costs have greatly reduced over time, and their longevity has made them more popular. LED grow lights are often priced higher, watt-for-watt, than other LED lighting, due to design features that help them to be more energy efficient and last longer. In particular, because LED grow lights are relatively high power, LED grow lights are often equipped with cooling systems, as low temperature improves both the brightness and longevity. LEDs usually last for 10,000 – 50,000 hours until LM-70 is reached.
Third generation: High-intensity discharge (HID) lamps
is regarded as the third generation of light sources.Fluorescent lighting was formerly the most common type of indoor grow light but HID lights have surpassed them. High-intensity discharge lamps have a high lumen-per-watt efficiency. There are several different types of HID lights including mercury vapor, metal halide, high-pressure sodium and conversion bulbs. Metal halide and HPS lamps produce a color spectrum that is somewhat comparable to the sun and can be used to grow plants. Mercury vapor lamps were the first type of HIDs and were widely used for street lighting, but when it comes to indoor gardening they produce a relatively poor spectrum for plant growth so they have been mostly replaced by other types of HIDs for growing plants.
All HID grow lights require an electrical ballast to operate, and each ballast has a particular power rating. Popular HID ratings include 150W, 250W, 400W, 600W and 1000W. 600W HID lights are the most electrically efficient as far as light produced, followed by 1000W. A 600W HPS produces 7% more light than a 1000W HPS.
Although all HID lamps work on the same principle, the different types of bulbs have different starting and voltage requirements, as well as different operating characteristics and physical shape. Because of this a bulb won't work properly without a matching ballast, even if the bulb will physically screw in. In addition to producing lower levels of light, mismatched bulbs and ballasts will stop working early, or may even burn out immediately.
Metal halide (MH)
bulbs are a type of HID light that emit light in the blue and violet parts of the light spectrum, which is similar to the light that is available outdoors during spring. Because their light mimics the color spectrum of the sun, some growers find that plants look more pleasing under a metal halide than other types of HID lights such as the HPS which distort the color of plants. Therefore, it's more common for a metal halide to be used when the plants are on display in the home and natural color is preferred. Metal halide bulbs need to be replaced about once a year, compared to HPS lights which last twice as long.Metal halide lamps are widely used in the horticultural industry and are well-suited to supporting plants in earlier developmental stages by promoting stronger roots, better resistance against disease and more compact growth. The blue spectrum of light encourages compact, leafy growth and may be better suited to growing vegetative plants with much foliage.
A metal halide bulb produces 60–125 lumens/watt, depending on the wattage of the bulb.
They are now being made for digital ballasts in a pulse start version, which have higher electrical efficiency and faster warmup. One common example of a pulse start metal halide is the ceramic metal halide. Pulse start metal halide bulbs can come in any desired spectrum from cool white to warm white and even ultraviolet-heavy.