Today, more growers are moving away from traditional HID and fluorescent T5 grow lights and are installing LED lighting. LEDs emit less heat than HID sources which means that the proximity of LED grow lights to the canopy varies from that of traditional grow lights. It is important to also understand how optimal grow light distance impacts the different phases of plant growth.
An article from BIOS outlines the different lighting needs for a variety of plants (including cannabis), according to their growth stage. It also addresses how to determine the proper distance of LED lighting from the plant canopy to nourish plant growth, as well as the importance of PPFD (PAR), and other popular grow light terminology.