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High Performance Lighting Guide

Linear Fluorescent Lamps

Development over time has generally improved efficiency and reduced the physical size of linear fluorescents. In addition to requiring less mounting space, the light from more slender fluorescents is better concentrated and can be more effectively directed by reflective surfaces on the fixture.

Linear fluorescents are classified by their diameter, expressed in 1/8-inch units. While the old T-12 fluorescent is 12/8 in. (1 1/2 in.) in diameter, today’s most common linear fluorescent is the T-8 at 1 in. diameter. Also common, under cabinet lighting and some of the newest technology uses T-5 lamps, 5/8 in. diameter. There are even T-4, T-2, and T-1 lamps, most of which are highly specialized for unique applications. The performance characteristics of some common linear fluorescent lamps are shown in the table below.

Linear fluorescent lamps, T-12, T-8, T-5, from top to bottom. Click for larger image.

T-8 lamps are very cost effective and are recommended where their physical size is acceptable. Many of the recommended fixtures shown in the designs use T-5 linear fluorescent lamps. The proper dimming ballast allows dimming for any of the linear fluorescent lamps. This guide does not discuss T-12 lamps because the technology is obsolete for high performance purposes.

Currently there are two generations of T-5 lamps in use: the original preheat technology and the newer high efficiency technology. Table 2 (above) shows that the new T-5 lamps can provide as much as two times the lumens per watt output compared to old T-5 technology. Thus, for equal illumination with the older T-5 lamp, it may be necessary to use two fixtures or a double lamp fixture to equal the lighting output of a new T-5 fixture.

The new T-5 technology was developed in Europe and thus the nominal 2 ft, 3 ft, and 4 ft lamps, being metric sizes, are slightly shorter than the nominal length and may only be used in fixtures specifically designed for their use.

Recommended Specifications

Dimming: The proper ballast allows for dimming with linear fluorescent lamps.

Dimensions: The lamp recommended by the fixture manufacturer should be used, as there are important differences in lamp size and base configuration. Each lamp must match the fixture ballast.

Cost and Availability

With linear fluorescents, the cost range is basically driven by how new the lamp technology is. The old, 40W T-12 cool white lamp (not recommended for any high performance lighting application) may sell for less than $2. The 32W T-8, today’s most commonly used lamp, costs approximately $2.50.

T-5 lamps, used in strip lights and under cabinet lights are produced with both old technology and new technology. Old technology lamps that come in 4, 6, 8, and 13W sizes are principally used in under cabinet fixtures are available at hardware outlets and cost up to $6 depending on size. The new, high efficie ncy T-5 lamps come in 14, 21, 28, and 35W sizes, are used in strip lights and under cabinet fixtures, and are generally available at electrical supply houses, not hardware outlets. A 4 ft, 28W lamp costs approximately $7.50. The preferred light color (80 CRI, 3000 K) may not be readily available in the newer T-5 lamps and could require ordering.

Linear fluorescent lamps are available in a range of sizes and wattages from numerous manufacturers. Depending on tube diameter and length, some linear lamps are available at hardware outlets, and some are stocked at electric supply houses. The preferred light color (80 CRI, 3000 K) may not be readily available in the newer T-5 lamps and could require ordering. Electric supply houses can usually get bulbs within one week even if they need to be special ordered.