We all know that plants need light for photosynthesis and that without photosynthesis there would be no energy for growth and flowering. But what is less understood is that it is only certain wavelengths of light that can be absorbed by chlorophyll cells in plant leaves and put to use. Grow lights are designed to mimic natural light and in particular emit a concentrated light at the “absorbable wavelengths.” There are three main grow light technologies on the market which we explore further below.
Lets start with indoor LED grow lights as these are growing rapidly in popularity among gardeners and plant growth experts. Key benefits include a lower initial cost, better energy efficiency and a long lifespan. Most gardeners choose a combination of red and blue lights as these match up with the maximum chlorophyll absorption points on the electromagnetic spectrum. LED lights have a low heat signature which means they can be placed close to the growing plant without risk of dehydration or scorching. They can be plugged into standard household electrical systems without the need for voltage ballasts.
One of the concerns that grow light gardeners have with fluorescent bulbs is that they produce a relatively dispersed light. However new models are emerging including compact fluorescent grow lighting systems which have special reflectors designed to direct the light in a concentrated manner on the growing plants. Higher output bulbs are also available. Fluorescent grow lights have been shown to be effective at promoting seedling growth and for getting cuttings rooted.
The main types of HID (Higher Intensity Discharge) grow lights used by indoor gardeners are High Pressure Sodium lights which emit light at yellow/orange wavelengths and Metal Halide which emit at blue wavelengths of light. Both are highly effective plant grow lights with a strong intensity. They are often used in combination, sometimes even positioned on the same fixture so they can be used alternatively.