HPS grow light or High-pressure sodium lamps is a High-intensity discharge (HID) form of lighting that is commonly used as indoor grow lights for hydroponic growth. The HPS light operates when an electrical current is run through an arc tube that has been filled with a gas. In this case, the gasses found within an HPS globe is a mixture of sodium and an inert gas Xenon. HPS bulbs are often used for flowering specifically because this technology puts off a very deep red wavelength, which is why it is best for flowering. This type of light forces bulbs to develop dense, robust buds.