First some terminology: LED is short for Light Emitting Diodes and the lights take the form of a tiny semiconductor chip that generates light by emitting electrons. HID stands for Higher Intensity Discharge and is a loose classification that groups together metal halide lights, high pressure sodium lights and mercury vapor lights.
HID lights have been used for many years by grow light gardeners. They emit a strong light that produces energy for photosynthesis and encourages plant growth, seeding and flowering. But in recent years, on the back of new technologies, indoor LED grow lights are starting to gain in popularity for a number of reasons.
LED grow lights are considerably more environmentally friendly that HID grow lights. They are highly energy efficient and do not contain mercury. Some LED lights can even be powered via solar panels. HID light is around 35% efficient with the remaining 65% of energy being released as heat. LED lights have a much lower heat signature. Plants need less watering, are less prone to scorching and there is no need for heat extraction fans or air conditioning.
When it comes to the light color spectrum, a key advantage of LED grow lights is that they can be manufactured to release light that corresponds exactly with the maximum chlorophyll absorption points on the electromagnetic spectrum. A typical set up includes four lights, two red and two blue. While HID lights also release red and blue light at appropriate wavelengths, they also release more non-absorbable light than LED lights.
Finally, the average life span of LED lights is longer than for HID lights. While HID lights typically last for 5,000 hours, LED lights have a life span between 50,000 and 100,000 hours. The costs of accessories also tends to be lower as air conditioning and high voltage stability ballasts are typically not needed.