Houseplants Under Lights

Lesson 1: Natural lighting vs. Artificial Lighting

Artificial Lighting

Supplemental lights are the easiest way to overcome the lack of natural lighting. There are many types of lights available for indoor gardeners. The various types of light bulbs emit different wavelengths on the light spectrum. The light wave spectrum ranges from ultra violet to infrared (the orange and red end of the spectrum). The visible portion of the light spectrum is from violet to red. These are the colors that we can see. Plants may be harmed by ultra violet light that, fortunately, is screened out by most glass.

Plants need the full range of the visible light spectrum for successful photosynthesis. Photosynthesis is the process that turns carbon dioxide, water and light into the carbohydrates used by the plant. These carbohydrates are further processed into the various compounds needed by a plant for growth.

The distance between the light and the plant determines the amount of light energy actually received by the plant. More light is received when the lights and plants are a short distance apart. You will prove this using your light meter.

What Light Bulbs are Available to the Indoor Gardener?

The three most commonly available lights for the indoor gardener are incandescent, fluorescent, and halogen. The advantages and disadvantages of each of these are discussed below.

Incandescent: These are the light bulbs we use in lamps and other lighting fixtures. Benefits: Low cost. Disadvantages: High heat output, poor light quality (for growth purposes), low efficiency in using electricity, and short life span.

Fluorescent lights: Available as cool white or warm white bulbs. Benefits: Low cost, cool running, better balance of light, and longer life span. Disadvantages: Light intensity decreases from the middle of bulb to ends of bulb, may need to balance the available light spectrum by combining cool and warm light bulbs for flowering plants, and low efficiency in use of electricity. NOTE: Many fluorescent lights are now 25 or 34 watts instead of the traditional 40 watts. Look for 40 watt bulbs.

Halogen Lights: These lights are rapidly becoming common in shoplight fixtures and lamps. They normally come in 150 and 300-watt bulbs. Benefits: Readily available, provide pleasing white light similar to natural light, provide full light spectrum for plant growth, provide higher level of footcandles per unit of electricity used than other bulbs. Disadvantages: Low efficiency in using electricity, medium life span of bulbs, and cost of bulbs.

Other Options

Visit a hydroponics or indoor gardening store. They have many additional types of lights available. The reason I am not discussing them is that the majority require expensive special equipment. Some even require having heavy-duty electrical outlets installed. If you are interested in exploring these alternatives, please talk to the store sales people for guidance.

What Do I Recommend?

After experimenting with different light bulbs, I've concluded that the majority of foliage plants grow well under cool white shoplights. The only plants that do not grow well in these conditions are the cactti and succulents that demand bright, western sunlight to thrive and flower. Therefore, I have chosen not to grow succulents needing higher light levels. I use a two-bulb fixture for plants requiring low to medium lighting and a four-bulb fixture for those needing higher light intensity.

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