1352 Fluorescent Lamps

Several smaller, yet brighter fluorescent systems (T2, T5 and T5HO) have flourished in recent years. Smaller systems have been effective in task lighting environments, where less light from a single source is needed. The reduction of unnecessary lighting reduces energy expenses.

T2 lamps

These are sub-miniature, 1/4" (0.25") diameter lamps that have side tabs instead of end pins. They are available in standard fluorescent colors of 3000K, 3500K, and 4100K with CRI in the mid-80s. They are rated with a lamp lumen depreciation of 0.95, and only lose 5% of their light output in the first 40% of rated life. T2 lamps have lamp efficacy ratings similar to compact fluorescent in the mid-60s.

Low profile fixtures used for task and under-counter lighting, showcase and decorative lighting have been made possible by these small diameter lamps. Their principal application, however, is for backlighting graphic display panels, which are starting to be done with highperformance light-emitting diodes (LEDs). The use of T2 lamps for this application is not expected to increase.

T5 lamps

The T5 lamps come in two distinct and different families—standard (high-efficiency) and high output (HO). These recently developed lamps should not be confused with older miniature preheat fluorescent lamps of the same diameter nor with the line of long compact fluorescent lamps of the same diameter.

Standard (high-efficiency) T5 linear lamps

These 5/8" diameter lamps (Figure 13-6) are equipped with miniature bi-pin bases and are powered by electronic ballasts. All the lamps in this family operate on the same current (170 ma) and have the same surface brightness for all wattages. For cove and cornice applications this is a distinct advantage.

Another reason the T5 lamp is suited for these applications is that they are designed to peak in their lumen rating at 35°C (95°F) vs. 25°C (77°F) for T12 and T8 lamps. This characteristic provides higher light output in confined applications where there is little or no air circulation. In indirect fixtures, this thermal characteristic increases efficiency and gives more usable lumens per watt.

Standard T5 lamps are 12-18% more efficient than T8 lamps (96-106 LPW) and 10-15% more efficient than the T5HO. T5s employ rare-earth phosphors with CRI greater than 80 and lamp lumen maintenance rated at 95%.

There are 4 sizes of standard T5 lamps as shown in Table 13.11, all rated at 20,000 hours (at 3 hours-per-start).

Note that the 28-watt lamp (not quite 4' long) has an initial lumen rating the same as a 4' T8 lamp. However, the millimeter lengths and miniature bi-pin bases preclude their use in standard length linear fluorescent systems and the high bulb-wall brightness limits their use to high ceiling applications because the visible tubes can create too much discomfort glare in low mounting height applications.

Table 13.11 Standard T5 Lamp Sizes (Source: Effective Lighting Solutions, Inc.)






mm/ (in)



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