The latest addition to indoor lighting options is lamps made from Light Emitting Diodes (LEDs). LEDs create little heat and are only about 3″-4″ deep, so they work well in closets, or spaces where height is an issue. LEDs are also very efficient, using less hydro than Metal Halide, High Pressure Sodium and even Fluorescents.
In an LED lighting system each diode emits light in a narrow spectrum. The spectrum is determined by the minerals used to make them. This allows LED’s to be designed to provide the plants with exactly the spectrum that they need for maximum growth. By tailoring the diode spectrums to the plants requirement, LED’s produce more PAR (Photosynthetically Active Radiation) than HID lamps.
PAR – The light that plants use is known as Photosynthetically Active Radiation. Humans see light best in the yellow-green wavelengths around 550 nm. Plants make most use of light in the red and blue spectrums in the range of 400-700 nm.
HPS lamps deliver more total light per watt of input, but LEDs are twice as efficient in PAR light per watt. LED fixtures are more expensive than HID lights, but they will save money in the long run.