Plants derive their food energy and drive many essential cellular functions with light, so good-quality illumination is essential for plant health. Outdoors, the sun provides adequate levels of the right wavelengths that flora need, at the time they need them. Indoors, proper plant lighting has traditionally been a tricky, hot and expensive problem. Recent advances in light emitting diodes hold the promise of doing away with many of the challenges presented by other types of grow lights.
A Brief History of LED Lights
Light emitting diodes were discovered in 1907, but it wasn't until 1962 that the first visible-spectrum LEDs came into practical use. When electricity flows in one direction through a semiconducting material, electrons release photon energy, which is light. Semiconducting materials so far discovered to produce light at room temperatures include gallium arsenide, silicon germanium and indium phosphide alloys. This is a strong area of technological research, with constant advancements in available colors, light intensities, efficiencies and sizes.
Plants and Light
The sun emits the full spectrum of electromagnetic energy, of which a small part is visible light. Plants use visible light, but not all wavelengths within that band. Blue light waves, which are the shortest waves of visible light (400-450 nanometers), provide the photon energy to convert carbon dioxide and water into glucose and oxygen. This chemical reaction is known as photosynthesis, which provides food for plants, and, ultimately, for all life on earth, as animals eat those plants and carnivores eat the herbivores.
Red light (650 nanometers) absorbs into certain protein structures in plants, which eventually trigger flower and fruit formation. Plants use other color wavelengths of light either much less efficiently or not at all.
LED Grow Light Advantages
Being a solid-state device, light emitting diodes are less susceptible to breakage than other types of lights. They are also significantly longer-lasting. An LED can have the lifetime of up to 50 incandescent, or four fluorescent lights. LEDs are less toxic than fluorescent lights, which are made with mercury and therefore must be disposed of carefully. LED's are much more efficient than incandescent bulbs, which lose much of their energy to heat instead of light. The cool-running lights therefore reduce air-conditioning needs as well.
LED Grow Light Availability and Cost
Being a fairly new technology, LED's can still be more expensive to purchase initially, but as mass-production techniques catch up with demand, prices are falling dramatically. At first, LEDs only gave off red light, but advances since then have produced light in almost every color of visible light, including blue, which became commercially available in the early 1990s. LED's are rapidly becoming the light of choice for indoor growing needs.
Optimal Color Proportions for Plants
LED grow lights embed blue and red diodes in panels, giving an overall purple appearance to them. Blue is needed in greater concentration than red. Generally, 10 blue lights for every red light is sufficient to ensure good plant growth. Distance to the lights is important, too. LED grow lights are usually made to be suspended above the leaves at a distance of 3 inches to no more than a foot.