Last week I said I would cover indoor lighting, so here it goes. Not every light bulb will work for growing plants indoors. The quantity and quality of light it produces can vary greatly. Plants use large amounts of red and blue light, lesser quantities of other colors and very little green, which is the color they reflect back to our eyes. The measurement scale of the color of light is expressed in the temperature scale of degrees Kelvin (K).

Sunlight at noon on a slightly overcast day is around 6,500K. A normal incandescent light is much cooler, around 2,800K, while a cool white bluish colored fluorescent light is a warm 4,100K. I know that it sounds odd to say that a yellowish-red light bulb that produces heat is cooler than a bluish colored fluorescent light, but it is true when you are only looking at the colors of light and not the kind of bulbs producing the light. Bulbs with color temperatures below 5,000K look more yellow or red, while bulbs rated between 5,000 and 6,000K are viewed as white and bulbs above 6,000K tend to look blue.

Some light bulbs are sold as "daylight," "sunlight," "natural," "balanced" or "wide spectrum." These terms mean the bulb is producing a color of around 5,000 to 6,000K. On the other hand a "full-spectrum" bulb produces a light that covers the entire range of visible light (400-700nm) without gaps in its spectral output. I have grown aquarium plants and vegetable transplants under full spectrum lights and a mix of cool and warm fluorescent lights, and the plants lit by full spectrum bulbs easily outgrew the others.

Old incandescent bulbs have an efficiency rate around 5 percent, and the spectrum of light produced is not ideal for growing plants. Incandescent bulbs also produce a large amount of heat, which will increase cooling costs.

High output full spectrum fluorescent lamps are a great choice for indoor plant growth. They are 3-7 times more efficient than incandescent bulbs but need to be placed close to the plant. Compact fluorescent bulbs can be good for growing a single plant in a room away from windows. Newer fluorescent bulbs are only 5/8 inch in diameter, while old bulbs are an inch and half in diameter. The new bulbs produce more light and heat but use less electricity. The new bulbs cost more and require a new fixture.

HID lamps are typically used for streetlights or for warehouses and greenhouses. They are used by home growers who are determined to get the most light possible. They produce a huge amount of heat and can't be placed near plants. They may need ventilation fans installed.

LED's (Light Emitting Diodes) are relatively expensive but use very little electricity, produce almost no heat and last much longer than all other bulbs.

I have a GlowPanel 45. This one-foot square panel of LEDs uses only 28 watts and can replace a 250-watt metal-halide grow light. It does so without producing the heat of a light bulb, too. I have tested it with my regular fluorescent grow light. I planted the same seeds in two identical trays. There were tomato, beans, peppers and cilantro. The seedlings growing under the bright red and blue LEDs of the GlowPanel 45 were sturdy and stocky plants with good dark green leaves. In the same room, the plants under my regular grow light were tall, spindly and pale green.

The only drawback that I see is the unusual color. The LED bulbs in GlowPanels are intensely blue and red. Combined, they produce a purple glow that takes some getting used to. The green leaves look strange under the light, but when the light is off, the good green color is obvious. If your local garden center doesn't have them, check them out at www.glow-panel.com.

Email questions to Jeff Rugg at [email protected]. To find out more about Jeff Rugg and read features by other Creators Syndicate writers and cartoonists, visit the Creators Syndicate website at www.creators.com.