more expansive than incandescent light bulb (3 to 10 times), because of their long service lives
(16,000 to 15,000 hours) and high efficacy values, their use results in net savings. The comparison
among different types of fluorescent lights is shown in Table 12.5.
Another common type of lighting system is the high-intensity discharge (HID) lamps
(Figure 12.17). They have the highest efficacy values and the longest service life of any light-
ing systems. The HID lamps are commonly used in indoor arenas and outdoor stadiums. As
you know from your experience, they have low color rendition index, and when you turn
them on, it would take a few minutes before they produce light. The comparison among dif-
ferent types of HID lights is shown in Table 12.6.
The newest type of lighting systems is LED (light emitting diode) lights. They have become
popular alternative to incandescent Christmas lights. They last longer than conventional
incandescent lights with service life of approximately 20,000 hours. They also use much less power
and operate at cooler temperatures, so they reduce fire hazard during the holiday season. Increas-
ingly, they are becoming popular alternatives in other applications such as traffic lights, street lights,366 Chapter 12 Electric Current and Related Parameters
TABLE 12.5 Comparison of Fluorescent Lights
Fluorescent Efficacy Lifetime Color Rendition Index Color Temperature
Lighting Type (lumens/watt) (hours) (CRI) (K)Straight tube 30 –110 7,000 – 24,000 50 – 90 (fair to good) 2700 – 6500
(warm to cold)Compact 50 –70 10,000 65 – 88 (good) 2700 – 6500
fluorescent lamp (warm to cold)
(CFL)■Figure 12.17
A schematic of high intensity
discharge lamp.
Source:DOE’s Office of Energy
Efficiency and Renewable
Energy.Vacuum
Arc tube
Outer
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