Artificial Lights for Indoor Plants

Date: April 1989 (Revised April 1995)

Source: NDSU Extension Service Horticulturists

When you use artificial light as the only light source for indoor plants, fluorescent tubes or commercial grow lights are probably the best. Place these lamps near the plants; they give a fairly high light intensity with a minimum amount of heat.

For small plants, place fluorescent fixtures about 12 inches above the pot rims. The effectively lighted area then extends about two inches beyond a line directly under the edge of a fluorescent lamp reflector. Replace tubes or grow lights every year because they lose intensity with age.

Light duration is important when you grow flowering plants under artificial lights. The influence of lights on flowering plants is classified into three groups:

short day plants - initiate flowers with short days and long nights

long day Plants - initiate flowers with long days and short nights

day-neutral plants - bloom under either short or long-day conditions

In general, most short day plants should have about 12 hours of light and 12 hours of darkness.

Typical short day plants are aster, salvia (SALvee-ah), poinsettia, and kalanchoe (KAL-an-KO-ee).

Most long day plants should have about 16 hours of light and 8 hours of darkness each day. Common long day plants are hibiscus, larkspur and delphinium (del-FIN-ee-um).

Flowering plants like light geranium, pansy and snapdragon are day-neutral and only slightly affected by day length.

When growing foliage plants under lights, or when starting bedding plants for future transplanting outside, use light periods of 12 to 14 hours during each 24 hour period.