For many plants, flowering is triggered by light exposure, including not only the length of time the plants receive light, but the brightness of the light they receive and how near the lights are. Control these variables with indoor lighting so your plants have even, bright light.
African violets need bright, indirect light. To bloom, they need even light exposure. An optimum 16 hours of light and eight hours of dark will encourage the best blooms. Incandescent lighting is enough for African violets, but the heat can damage the plants if the bulb is too close, so fluorescent lights are preferred. Regular fluorescent tubes provide good light, but fluorescent bulbs with managed spectrum for plant growth are the best. Two 40-watt tubes hanging 12 to 15 inches above the plants will provide ideal light that will promote flowering.
Poinsettias can be forced to bloom by managing the light and darkness the plant receives. Poinsettias should be kept on a strict schedule of eight hours of bright light and 16 hours of complete and absolute darkness for four weeks beginning about 12 weeks before colored bracts are desired. Indoor fluorescent tubes are an excellent method of providing even, bright light for poinsettias. Any fluctuation in the light/dark schedule will upset the red bract formation; a timer is a good idea. Six to eight hours of bright, evenly timed light per day will keep a blooming poinsettia looking good. Using indoor grow lights is an ideal way to prolong the beauty of your poinsettia.
Geraniums make ideal houseplants. If you grow them outdoors during the summer, pot some and bring them indoors during the winter to enjoy their blooms. Geraniums from seed live for about 18 months. Although they will become somewhat dormant when you first bring them indoors, if you provide bright light, they will perk up and bloom again. Grow lights are also helpful for starting geranium cuttings indoors. Adjust tube fluorescents so they are about 8 inches above the plants. More distance can cause geraniums to become leggy.
Orchids respond to bright indoor plant lights by producing elegant blossoms. Orchids need more brightness than other houseplants. A fixture with four wide-spectrum grow-light fluorescent bulbs should provide 2000 foot candles of light, which is ideal for orchids. About eight hours per day will provide enough light for good orchid growth.