 But, in the higher latitudes, there are periods of the year where sunlight is scarce, and additional sources of light are indicated for proper growth.HPS lights may cause distinctive infrared and optical signatures, which can attract insects or other species of pests; these may in turn threaten the plants being grown.High-pressure sodium lights emit a lot of heat, which can cause leggier growth, although this can be controlled by using special air-cooled bulb reflectors or enclosures.