LED Basics

UNDERSTANDING HOW A LED MAKES LIGHT

LED's are essentially small "light bulbs" which do not contain a filament that can burn out or get extremely hot, and instead use a diode. A diode is the simplest form of a semiconductor, which is able to convert electrical current into light. When turned on, current flows from the anode side to the cathode side, passing over holes within the diode, where it re-combines and releases energy in the form of photons. This effect is known as electroluminescence, and the color of light emitted is determined by the band gap and materials between the anode and cathode. Unlike traditional bulbs, colored LED's produce very narrow bandwidths of light measured in nano-meters, abbreviated nm. For example, a LED rated at 660nm peak output, emits trace amounts of light at 640nm and 680nm (bottom photo), focusing the vast majority of it's light directly at 660nm.

Standard HID light bulbs emit a broad spectrum of light from 400-700nm, which is very inefficient for plant growth. This kind of light is labeled "white light", as it appears white in color to the human eye. All in all, about 30% of the light emitted by these broad spectrum "white" sources, is converted by plants via photosynthesis, while the rest is wasted. It is for this reason that LED Grow Lights have been developed, as they are able to tailor their spectral outputs to the wavelenghts used most efficiently for photosynthesis. This allows nearly 100% of the light created to be used by plants, which is why you need less power to achieve the same results with LED as you are accustomed to with HID.