T12 Vs. T8 Bulbs

Fluorescent lighting

T12 and T8 bulbs are straight, tubular fluorescent light bulbs released simultaneously in 1938 for commercial use. Several differences exist between the two bulbs.

Diameter

Both the T12 and T8 bulbs are available in a wide range of lengths. However, the diameter of the cylindrical bulbs is constant for each model. While the 'T' designates the bulb as having a tubular shape, the following numerical value designates its diameter in eighths of an inch. The T12 bulb is 12/8 of an inch (1 1/2 inches) and the T8 is 8/8 of an inch (1 inch).

Brightness

Although both models are available, the T8 is gradually replacing the T12 for a number of reasons. T8 bulbs shine brighter than T12 bulbs of comparable length after any given period.

Efficiency

T8 bulbs are more energy efficient than T12 bulbs. They produce a greater amount of light while using a smaller amount of energy.

Ballasts

While T12 and T8 bulbs work in the same type of socket, they use different ballasts. The T8 model uses an electrical ballast while the T12 uses a regular (magnetic) ballast. According to the Applications Team website, sponsored by the U.S. Department of Energy, lamps can be retrofitted with T8-friendly ballasts.

Coloring

The color rendering index (CRI) also differs between the two bulbs. In fluorescent light bulbs, a higher CRI means there is a greater variation of color visible to the human eye. The CRI for T12 bulbs is usually 60 to 65 while the CRI for T8 bulbs ranges from 75 to 95.

References

• The Fluorescent Lamp: The Story Behind This Account of Fluorescent Lamp Development
• Aquatic Technology: Fluorescent Lamps and Ballasts
• Applications Team: T-8 Lamp Retrofits

Resources

• The Encyclopedia of Alternative Energy and Sustainable Living
• Energy Star