In general, grow lights are capable of emitting an electromagnetic spectrum necessary for photosynthesis. LEDs have become an increasingly viable alternative to the metal halide and high pressure sodium bulbs that have been used in the past. Earlier versions were usually not bright enough to offer an effective alternative to HIDs, but today’s three watt and five watt designs are often excellent alternatives. They have been even been clustered in 1200 watt configurations. NASA has now tested such designs for possible use on space missions to facilitate photosynthesis. Their low energy requirements and low heat output are considered potentially advantageous in such applications.
This newer type of grow bulb can be configured so that it only emits the wavelengths that correspond to the so-called absorption peaks of the usual photochemical processes of a given plant type. Chlorophyll and carotenoids have multiple absorption peaks, and these can be addressed by configuring diodes of varied colors that overlap with these peaks. Blue diodes in the approximate 450 nm range are advantageous for vegetative growth, while red diodes in the 600-640 nm range are more often used for growing flowers and fruit.
The ability to “fine-tune” these creations by mixing diodes to optimize production of the right wavelengths makes them far more efficient than their traditional counterparts. The illumination produced falls more perfectly within the spectrum of photosynthetically active radiation.
Such illumination can also be directed more precisely. Reflectors are not needed to “focus” the illumination where it is needed. For example, a florescent tube emits illumination in all directions, which is inefficient. A reflector is required to better direct the illumination where it is needed.
Unlike florescent grow tubes, diode clusters do not require ballasts. They also generate much less heat than fluorescents, high pressure sodium and metal halide bulbs. The fact that they generate less heat often allows more time between watering events. Also, leaves are less likely to get burned on the edges.
Standard florescents have been traditionally used for indoor germination and for growing seedlings. They are also used for growing vegetables and herbs. Full-spectrum “daylight” bulbs (5000 K) are commonly used as grow bulbs. They have a usable life span of 20,000 hours, which is much more than that of MH, incandescent or HPS bulbs. However, such a life span still falls far short of that offered by LEDs. Compact fluorescents have a usable life span of about 10,000 hours, and they require reflectors to properly direct the illumination.
Metal halide bulbs have tended to replicate a bright summer day. However, today’s MH lighting is available in cool white, warm white and even heavy UV types. Still, energy consumption is far greater than that of modern diode fixtures, and the amp rating is much higher. They are typically rated at about 5000 hours of life, about 5-10 percent of the life span of diode-type fixtures.
A major drawback disadvantage to HPS illumination is that the orange/red spectrum created tends to produce a taller, leggier plant. However, they can facilitate the growth of fruit and flowers, so they may be used in conjunction with metal halide or fluorescent bulbs, depending upon the application. Another drawback is the amount of heat that these fixtures typically generate. The amp rating or requirement is also much greater than that of fixtures creating illumination via diodes.
The use of incandescent bulbs for growing plants has been limited by their relatively low color temperature of 2700 K, which puts the illumination at the red end of the spectrum. Some incandescent bulbs coated with blue filter material have been marketed as grow bulbs, but they are limited in two key ways. They generate a large amount of heat, and they are therefore very energy inefficient. They also only last about 750 hours. Contrast that with the life span of modern diode-based fixtures, which are generally rated at 50,000 hours or more.
Today, diode-based grow fixtures are used by hobbyists and commercial growers alike. Indoor, sustainable urban gardening combines hydroponics and grow fixtures. Greens, vegetables and fruits can all be grown in these indoor locations. Grow bulbs are being considered in the production of algae that can be effectively used as a biofuel source. This form of algae production can yield a carbohydrate/protein solid that can be used as an animal feed.
Growers of medical marijuana have increasingly turned to diode-based designs. Commercial growers can cut their electricity costs by as much as 40 percent or more by switching to Such fixtures. Less heat generation means a reduced need for exhaust fans. Less heat may also enhance quality because THC is known to degrade in the presence of heat. This gives LEDs the edge over MH bulbs, because a given strain of cannabis will produce more THC when grown under such lighting.
Hobby gardeners love these fixtures because they make gardening possible on a year-round basis. Hobbyists often enjoy growing herbs, produce and even orchids. Some start the germination of their seedlings indoors in advance of the outdoor growing season. In the past, such gardeners relied extensively on HID fixture. Now, newer diode-based fixtures are capable of promoting photosynthesis in basic greens as well as watermelons and cacti.
LED grow lights are increasingly chosen for more applications than their counterparts because they use less energy, generate less heat, and better produce illumination of the type needed for photosynthesis. Red and blue diodes can be combined to create appropriate illumination. They also offer much longer life spans than all other competing types of bulbs.