T12 Fluorescent Vs. T8 Fluorescent

Availability and Cost

• T12 fluorescent bulbs are widely used for interior lighting and have a cheaper initial cost. You can buy T12 bulbs in lengths of 18, 24, 36, 48, 72 and 96 inches and in U-shapes that are 24 inches long. A VHO (very high output) T12 bulb uses more electricity but produces more light. You can usually buy T12 bulbs in hardware and department stores.

  If you want a bulb to produce a particular light spectrum for growing plants, then a T8 is usually cheaper. You can buy T8 bulbs that are 24, 36 and 48 inches long and in circular shapes. You can buy fluorescent grow lights at most garden supply centers.

  Both T12 and T8 bulbs will fit into the same fixture.

Efficiency

• The efficiency of a T12 bulb deteriorates more quickly than a T8 bulb. Fluorescent bulbs are rated by their output of light measured units called lumens. Ian Philips writing in the Bigelow Site reports that a T12 produces 10 percent fewer lumens after 3,000 to 4,000 hours of operation and 20 percent fewer lumens after it runs 7,000 hours; a T8 produces 10 percent fewer lumens after 7,000 hours. Pushed by federal minimum energy standards for fluorescent bulbs, the T8 is replacing the T12 for interior lighting.

Fluorescent Grow Lights

• If you are using fluorescent light for growing, you need to consider the "color" of light, determined by a phosphor coating on the interior of the bulbs. The blue and green range of the light spectrum, called cool colors, mimic the quality of light given by the sun in the spring through mid summer. Cool light stimulates plant growth and is good for growing seedlings and encouraging vegetative growth. These bulbs are usually marketed as "cool" or "cool white." Red and orange light, warm colors, mimic the quality of light given by the sun in late summer and early fall. Warm light stimulates flowering and fruiting. Over their growth cycle, plants need a combination of cool and warm light, but different plants respond differently to lights of different color. Determine the light needs of your plants before selecting any fluorescent grow light. Fluorescent grow lights are easier to find in the T8 size.

Full-Spectrum Bulbs

• Cool fluorescent bulbs are used for interior lighting. Full-spectrum grow lights, usually marketed in increasingly popular T8 size, contain the full range of light. You can achieve a balance of colors by combining cool and warm fluorescent bulbs.