LIGHTING SYSTEMS

Introduction

Lighting accounts for a significant portion of the energy use in commercial buildings. For instance, in office buildings, 30-50 percent of the electricity consumption is used to provide lighting. In addition, heat generated by lighting contributes to additional thermal loads that need to be removed by the cooling equipment. Typically, energy retrofits of lighting equipment are very cost-effective with payback periods of less than two years in most applications.

In the United States, lighting energy efficiency features are the most often considered strategies to reduce energy costs in commercial buildings, as shown in Table 5.3. The data in Table 5.3 is based on the results of a survey (EIA, 1997) to determine the participation level of commercial buildings in a variety of specific types of conservation programs and energy technologies.

To better understand the retrofit measures that need to be considered in order to improve the energy efficiency of lighting systems, a simple estimation of the total electrical energy use due to lighting is first considered:

TABLE 5.3

Level of Participation in Lighting Conservation Programs by US Commercial Buildings

Lighting Retrofit

Percent Participation in Number of Buildings

Percent Participation in Floor Area of Spaces

Energy-efficient lamps and ballasts

31

49

Specular reflectors

18

32

Time clock

10

23

Manual dimmer switches

10

23

Natural lighting control sensors

7

13

Occupancy sensors

5

11

Source: EIA (1997).

where

NUim j = the number of lighting luminaires of type j in the building to be retrofitted. Recall that a luminaire consists of the complete set of a ballast, electric wiring, housing, and lamps.

WRLtimj = the wattage rating for each luminaire of type j. The energy use due to both the lamp and ballast should be accounted for in this rating.

Nh j = the number of hours per year when the luminaires of type j are operating.

j = the number of luminaire types in the building.

It is clear from Eq. (5.24) that there are three options to reduce the energy use attributed to lighting systems as briefly discussed below:

a. Reduce the wattage rating for the luminaires, including both the lighting sources (e.g., lamps) and the power transforming devices (e.g., ballasts) [thereby decreasing the term WRLiwij in Eq. (5.24)]. In the last decade, technological advances such as compact fluorescent lamps and electronic ballasts have increased the energy efficiency of lighting systems.

b. Reduce the time of use of the lighting systems through lighting controls [thereby decreasing the term NhJ in Eq. (5.24)]. Automatic controls have been developed to decrease the use of a lighting system so that illumination is provided only during times when it is actually needed. Energy-efficient lighting controls include the occupancy sensing systems and light dimming controls through the use of daylighting.

c. Reduce the number of luminaires [thereby decreasing the term NLum j in Eq.

(5.24)]. This goal can be achieved only in cases where delamping is possible due to overillumination.

In this section, only measures related to the general actions described in items (a) and (b) are discussed. To estimate the energy savings due to any retrofit measure for the lighting system, Eq. (5.24) can be used. The energy use due to lighting has to be calculated before and after the retrofit, and the difference between the two estimated energy uses represents the energy savings.

Energy-Efficient Lighting Systems

Improvements in the energy efficiency of lighting systems have provided several opportunities to reduce electrical energy use in buildings. In this section, the energy savings calculations for the following technologies are discussed:

  • • High-efficiency fluorescent lamps
  • • Compact fluorescent lamps
  • • Compact halogen lamps
  • • Electronic ballasts

First, a brief description is provided for the factors that an auditor should consider in order to achieve and maintain an acceptable quality and level of comfort for the lighting system. Second, the design and the operation concepts are summarized for each available lighting technology. Then, the energy savings that can be expected from retrofitting existing lighting systems using any of the new technologies are estimated and discussed.

Typically, three factors determine the proper level of light for a particular space. These factors include age of the occupants, speed and accuracy requirements, and background contrast (depending on the task being performed). It is a common misconception that overlighting a space provides higher visual quality. Indeed, it has been shown that overlighting can actually reduce the illuminance quality and the visual comfort level within a space in addition to wasting energy. Therefore, this conception is important when upgrading a lighting system to determine and maintain the adequate illuminance level as recommended by the appropriate authorities. Table 5.4 summarizes the lighting levels recommended for various activities and applications in selected countries, including the United States, based on the most recent illuminance standards.

5.4.2.1 High-Efficiency Fluorescent Lamps

Fluorescent lamps are the most commonly used lighting systems in commercial buildings. In the United States, fluorescent lamps illuminate 71 percent of the commercial space. Their relatively high efficacy, diffuse light distribution, and long operating life are the main reasons for their popularity.

A fluorescent lamp generally consists of a glass tube with a pair of electrodes at each end. The tube is filled at very low pressure with a mixture of inert gases (primarily argon) and liquid mercury. When the lamp is turned on, an electric arc is established between the electrodes. The mercury vaporizes and radiates in the ultraviolet spectrum. This ultraviolet radiation excites a phosphorous coating on the inner surface of the tube, which emits visible light. High-efficiency fluorescent lamps use a krypton-argon mixture that increases the efficacy output by 10-20 percent from a typical efficacy of 70 lumens/W to about 80 lumens/W.

TABLE 5.4

Recommended Lighting Levels for Various Applications in Selected Countries

Application

Offices

France AEF

Germany

DIN5035

Japan JIS

United States/ Canada IESNA

General

425

500

300-750

200-500

Reading tasks

425

500

300-750

200-500

Drafting (detailed) Classrooms

850

750

750-1.500

1.000-2,000

General

325

300-500

200-750

200-500

Chalkboards Retail stores

425

300-500

300-1.500

500-1.000

General

100-1.000

300

150-750

200-500

Tasks/till areas Hospitals

425

500

750-1.000

200-500

Common areas

100

100-300

-

-

Patient rooms Manufacturing

50-100

1,000

150-300

100-200

Fine knitting

850

750

750-1.500

1.000-2,000

Electronics

625-1,750

100-1.500

1,500-300

1.000-2,000

Note: In Lux maintained on horizontal surfaces.

Improvement in the phosphorous coating can further increase the efficacy to 100 lumens/W.

It should be mentioned that handling and disposal of fluorescent lamps is highly crucial, because the mercury inside the lamps can be toxic and hazardous to the environment. A new technology is being tested to replace the mercury with sulfur to generate the radiation that excites the phosphorous coating of the fluorescent lamps. The sulfur lamps are not hazardous and would present an environmental advantage to the mercury-containing fluorescent lamps.

Fluorescent lamps come in various shapes, diameters, lengths, and ratings. A common labeling system used for fluorescent lamps is

where

F stands for the fluorescent lamp.

S refers to the style of the lamp. If the glass tube is circular, then the letter C is used. If the tube is straight, no letter is provided.

IV is the nominal wattage rating of the lamp (it can be 4, 5, 8, 12, 15, 30, 32, 34, 40, etc.).

C indicates the color of the light emitted by the lamp: W for white, CW for cool white, BL for black light.

T refers to tubular bulb.

D indicates the diameter of the tube in one-eighth inch (1/8 in. = 3.15 mm) and can be, for instance, 12 (D = 1.5 in. = 38 mm) for the older and less energy- efficient lamps and 8 (D = 1.0 in. = 31.5 mm) for more recent and energy- efficient lamps.

Thus, F40CW-12 designates a fluorescent lamp that has a straight tube, uses 40-W electric power, provides cool white color, and is tubular with 38 mm (1.5 in.) in diameter.

Among the most common retrofit in lighting systems is the upgrade of the conventional 40-W T12 fluorescent lamps to more energy-efficient lamps such as the 32-W T8 lamps. For a lighting retrofit, it is recommended that a series of tests be conducted to determine the characteristics of the existing lighting system. For instance, it is important to determine the illuminance level at various locations within the space, especially in working areas such as benches or desks.

5.4.2.2 Compact Fluorescent Lamps

These lamps are miniaturized fluorescent lamps with small diameter and shorter length. The compact lamps are less efficient than full-size fluorescent lamps with only 35-55 lumens/W. However, they are more energy efficient and have longer life than incandescent lamps. Currently, compact fluorescent lamps are being heavily promoted as energy-saving alternatives to incandescent lamps even though they may have some drawbacks. In addition to their high cost, compact fluorescent lamps are cooler and thus provide less pleasing contrast than incandescent lamps.

5.4.2.3 Compact Halogen Lamps

Compact halogen lamps are adapted for use as direct replacements of standard incandescent lamps. Halogen lamps are more energy-efficient, produce whiter light, and last longer than incandescent lamps. Indeed, incandescent lamps typically convert only 15 percent of their electrical energy input into visible light because 75 percent is emitted as infrared radiation and 10 percent is used by the filament as it burns off. In halogen lamps, the filament is encased inside a quartz tube that is contained in a glass bulb. A selective coating on the exterior surface of the quartz tube allows visible radiation to pass through but reflects the infrared radiation back to the filament. This recycled infrared radiation permits the filament to maintain its operating temperatures with 30 percent less electrical power input.

Halogen lamps can be dimmed and present no power quality or compatibility concerns as can be the case in compact fluorescent lamps.

5.4.2.4 Electronic Ballasts

Ballasts are integral parts to fluorescent luminaires, because they provide the voltage level required to start the electric arc and regulate the intensity of the arc. Before the development of electronic ballasts in the early 1980s, only magnetic or “core and coil” ballasts were used to operate fluorescent lamps. Although the frequency of the electrical current is kept at 60 Hz (in countries other than the United States, the frequency is set at 50 Hz) by the magnetic ballasts, electronic ballasts use solid-state technology to produce high-frequency (20-60 MHz) current. The use of high-frequency current increases the energy efficiency of the fluorescent luminaires because light cycles more quickly and appears brighter. When used with high-efficiency lamps (T8, for instance), electronic ballasts can achieve 95 lumens/W as opposed to 70 lumens/W for conventional magnetic ballasts. It should be mentioned, however, that efficient magnetic ballasts can achieve similar lumen/watt ratios as electronic ballasts.

Other advantages that electronic ballasts have relative to their magnetic counterparts include the following:

  • Higher Power Factor: The power factor of electronic ballasts is typically in the 0.90-0.98 range. Meanwhile, the conventional magnetic ballasts have a low power factor (less than 0.80) unless a capacitor is added as discussed in Section 5.2.
  • Fewer Flicker Problems: Because the magnetic ballasts operate at 60 Hz current, they cycle the electric arc about 120 times per second. As a result, flicker may be perceptible during normal operation, especially if the lamp is old, or when the lamp is dimmed to less than 50 percent capacity. However, electronic ballasts cycle the electric arc several thousand times per second and flicker problems are avoided even when the lamps are dimmed to as low as 5 percent of capacity.
  • Fewer Noise Problems: The magnetic ballasts use electric coils and generate audible hum, which can increase with age. Such noise is eliminated by the solid-state components of the electronic ballasts.
 
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