Landscape light bulbs furnish the exteriors of homes and businesses and can provide extra light to plants that need it.
The easiest way to provide supplemental light is to position an incandescent light bulb about 1 inch or so above a plant. It won't supply as much light as a "grow light" would, but it works well for plants with low light requirements. Incandescent bulbs prevent plants from stretching and becoming leggy. Fluorescent bulbs provide light from the blue spectrum, which helps keep plants short and bushy.
Flowering plants need additional light, requiring high-intensity discharge lamps or halogen lamps, which provide a light source much like the sun, but replacement bulbs are inexpensive. High-pressure sodium lamps provide red-spectrum light that many flowering plants require to bloom.
Handle both high-pressure sodium and high-intensity discharge lamps very carefully; they can blow up if dropped. All supplemental landscape light bulb lighting systems should be left on for 14 to 16 hours per day, and will add a few dollars extra to your monthly electricity bill.