ISAT 413 ─ Module II: Lighting

ISAT 413 ─ Module II: Lighting Topic 2: Energy efficient lighting technologies and their applications (1) • Variations in Lighting Energy Consumption Among Different Building Types • The Design of Energy-Efficient Lighting Systems • The Design, Applications, and Efficacy of Various Lighting Technologies • Lamps (with an energy recovery example) • Ballasts • Lighting Fixtures • Lighting Controls

Introduction • Lighting is an important electrical end use in every sector and building type across the United States and accounts for approximately one-fifth of national electricity use. • Researchers estimate that an additional 3 to 4% of national electricity use can be attributed indirectly to lighting because of the heat that lighting systems produce and the extra air conditioning energy that is therefore required to cool buildings. • In 1990, approximately 38% of commercial, 11% of residential, and 9% of industrial electricity consumption was attributable to lighting measures. The commercial sector consumes the majority of the electricity used for lighting in the United States. • There is great potential for saving electricity, reducing the emission of greenhouse gases associated with electricity production, and reducing consumer energy costs through the use of more efficient lighting technologies as well as advanced lighting design practices and control strategies.

Variations in Lighting Energy Consumption Among Different Building Types • The amount of energy consumed for lighting in a given building, and thus the potential for energy conservation, depends on a variety of factors: • The lighting levels. • The number of hours per year that the lighting equipment is in use. • The type of equipment used. • The design of the lighting system. • in general, lighting levels depend on the type of building and the type of activities within the building, and the age of the building. The annual hours of use for lighting equipment in a given building depend largely on the type of activity and the use of lighting control.

Lighting EUI (Energy Use Intensity) and Annual Hours of Use in the Commercial Sector (EIA, 1992) On average, lighting energy per household in the U.S. is estimated to be approximately 1,100 kWh/per (ranging from 1,000 to 3,000 kWh/yr or more).

The Design of Energy-Efficient Lighting Systems • Efficient, high-quality lighting design includes • Attention to task and ambient lighting─ For visual comfort and ease of visual transition between task and ambient spaces, the “ambient” lighting in a room should be at least one-third as bright as the lighting of the task areas (U.S. DOE, 1993). • Effective use of daylight ─ The effective use of daylight can be greatly enhanced by the overall architectural design of a building. More sunlight is available to a building design that maximizes surface area (e.g., a building that is U-shaped or has an interior courtyard). In addition, skylights, wide windowsills, reflector systems, louvers, blinds, and other innovations can be used to bounce natural light farther into a building. The use of window glazes can limit heat transmission while permitting visible light to pass through a window or skylight.

Effective use of lighting controls─ Lighting control systems and permanent dedicated fixtures are important components of efficient lighting systems. In order to complement other efficiency improvements, lighting designers can use lighting controls such as dimming systems to reduce lighting when it is not needed, and install permanent lighting fixtures that are dedicated to efficient lamps (e.g., compact fluorescent lamps go with hard-wire CFL fixtures, not retrofitting in incandescent fixtures). • Use of the most cost-effective and efficacious technologies ─ Lighting design that promotes energy-efficient lighting technologies can also influence the design and energy use of a building’s cooling system. Because efficient lighting systems produce less heat, the air conditioning system installed in new buildings with efficient lighting can have lower cooling capacities.

The Design, Application, and Efficacy of Various Lighting Technologies • Lighting system components can be broken into four categories: • Lamps • Ballasts • Fixtures • Lighting controls The purpose of a lamp is to produce light, and not just radiated power, there is no direct measure of lamp efficiency. Instead, a lamp is rated in terms of efficacy, which is the ratio of the amount of light emitted (lumens) to the power (watts) drawn by the lamp. The unit used to expressed lamp efficacy is lumens per watt (LPW). The theoretical limit of efficacy is 683 LPW and would be produced by an ideal light source emitting monochromatic radiation with a wavelength of 555 nm.

Lamps The Efficacies of Various Lamps / Light Sources Lamps also differ in terms of their cost, size, color, lifetime, optical controllability, dimmability, lumen maintenance, reliability, simplicity, and convenience in use, maintenance, and disposal, and environmental effects such as emission of noise, radio interference, and UV light.

Terms for Distinguishing Lamp Differences • Color temperature─ expressed in degrees Kelvin (K), is a measure of the color appearance of the light of a lamp. The concept of color temperature is based on the fact that the emitted radiation spectrum of a blackboady radiator depends on temperature alone. Lamps with low color temperature (3000 K and below, incandescent and warm-white fluorescent lamps) emit “warm” white light that appears yellowish or reddish in color. Lamps with high color temperatures (3500 K and above, cool-white fluorescent lamps) emit “cool” white light that appears bluish in color. • Color rendering index (CRI) ─ a measure of how surface colors appear when illuminated by the lamp compared to how they appear when illuminated by a reference source (either a standard daylight condition or a blackbody radiator) of the same color temperature. A lamp’s CRI indicates the difference in the perceived color of object viewed under the lamp and under the reference source. It’s maximum scale is 100. Incandescent lamps have CRIs close to 100, CRIs of 70 and above are considered good, while CRIs 20 and below are considered to be quite poor. • Optical controllability ─ describes the extent to which a user can direct the light of the lamp to the area where it is desired. It depends mainly on its fixture, e.g., incandescent lamps have good controllability due to its point light source from its small filament area.

Radiation Spectrum of Blackbody Radiator In 1900, Max Planck produced a derivation of the law of radiation which bears his name and precisely describes the spectral distribution of the radiation from a blackbody. The spectral blackbody emissive power as the function of wavelength (in mm) for blackbody emitters at several different temperatures is shown in the figure below. These curves are defined by Planck’s formula which reads:

Incandescent Lamps The incandescent lamp was invented independently by Thomas Edison in the United States and Joseph Swan in England in the late 1800s.An incandescent lamp produces light when electricity heats the lamp filament to the point of incandescence.

Incandescent Lamps In modern lamps the filament is made of tungsten. Because 90% or more of an incandescent’s emissions are in the infrared (thermal) rather than the visible range of the electromagnetic spectrum, incandescent lamps are less efficacious than other types of lamps. The two primary types of standard incandescent lamps are general service and reflector/PAR (parabolic aluminized reflector) lamps. General-service lamps (also known as “A-lamps) are the pear-shaped, common household lamps (see the previous slide). Reflector lamps, such as flood or spot lights, are generally used to illuminate outdoor areas or highlight indoor retail displays and artwork. (The characteristics and applications of A-lamps and reflector lamps are summarized in Tables 12B.3 and 12B.4.) Reasons for the prevalence of incandescent lamps include: Excellent CRIs and a warm color, easily dimmed, inexpensive, small, lightweight, can be used with inexpensive fixture, excellent optical control, no annoying noise, emit little or no harmful radiation, contain no toxic chemicals

Tungsten-Halogen Lamps Tungsten-halogen lamps (see Figure on the right produce bright white light and have color temperatures and CRIs that are similar to, or slightly higher than, those of standard incandescents. In addition, they have longer lives, can be much more compact, are slightly more efficacious, and better lumen maintenance than standard incandescent lamps.

Tungsten-Halogen Lamps Generally, tungsten-halogen lamps use a quartz envelope rather than a glass envelope, which allows the lamp to operate at a much higher temperature. In place of the normal inert gas fill, the tungsten-halogen lamps use a small amount of halogen gas, which reacts with the tungsten that deposits on the quartz envelope to make a volatile tungsten-halide compound; because tungsten-halide vapor is not stable at the temperature of the filament, the vapor dissociates and deposits the tungsten back onto the filament. The cycle is then repeated. This cycle does not necessarily return the tungsten to the same portion of the filament from which it evaporated, but it does substantially reduce net evaporation of tungsten and thus prolong the life of the filament. The net reduction of evaporation due to the halogen cycle is usually partially offset by running the filaments slightly hotter than in a standard incandescent lamp, so most tungsten-halogen lamps are designed to have slightly better efficacies and lifetimes than comparable standard lamps.

Tungsten-Halogen Infrared Reflecting (HIR) Lamp The efficacy of incandescent lamps (90%of energy radiated in the form of heat, infrared radiation) can be improved by reflecting the infrared portion of the spectrum back onto the lamp filament. HIRlamps use a selective, reflective, thin-film coating on the halogen-filled capsule or on the reflector surface. The coating transmits visible light but reflects much of the infrared radiation back to the filament, so it takes less electricity to heat it. (The characteristics and applications of HIR PAR lamps are summarized in Table 12B.6.) HIR lamps have a small market share due to their high cost. However, their price will be dropped after the U.S. Energy Policy Act (EPACT) increased the minimum lamp efficacies required for all incandescent reflector lamps. Note that the minimum required efficacies range from 10.5 LPW (for lamps of 40 to 50 watts) to 15 LPW (for lamps of 156 to 205 watts). Standard incandescent reflector lamps (50 to 75 watts) have efficacies of only 8 to 12 LPW, and altering their design to meet the EPACT requirements could result in lamps with only half of their current operating lifetimes.

Full-Size Fluorescent Lamps The scientific principles of fluorescent lighting were understood by the mid-1800s, however, the fluorescent lamps didn’t come into general use until 1950s.

Full-Size Fluorescent Lamps In a fluorescent lamp, gaseous mercury atoms within a phosphor-coated lamp tube are excited by an electric discharge. As the mercury atoms return to their ground state, ultraviolet radiation is emitted. This UV radiation excites the phosphor coating on the lamp tube and causes it to fluoresce, thus producing visible light. The efficacy of a fluorescent lamp system depends upon the lap length and diameter, the number of lamps per ballast, the temperature of the lamp (which depends on the fixture and its environment), and a number of lesser factors. Fluorescent lamps have long lives and fairly good lumen maintenance. While the standard phosphor (cool-white, CW, and warm-white, WW) lamps have CRIs of 50 to 60, the new rare phosphor lamps have CRIs of 70 to 80. Note that the lamp tubes with a diameter of 1.5 inches are called T12s, and tubes that are 1 inch in diameter are called T8s. The 8 and 12 refer to the number of eighths of an inch in the diameter of the lamp tube. (The characteristics and applications of 4-foot, standard phosphor T12 lamps are summarized in Table 12B.7.)

Triphosphor (Full-Size Fluorescent) Lamps Rare earth phosphor lamps are also called triphosphor lamps because they are made with a mixture of three rare earth phosphors that produce visible light of the wavelengths to which the red, green, and blue retinal sensors of the human eyes are most sensitive. The most efficacious of the fluorescent lamps available today are T8 lamps operating with electronic ballasts. The efficacy of two 32-W T8 lamps operating with a single electronic ballast is about 90 LPW, approximately 30% more efficacious than the more standard lighting system consisting of two 40-W T12 lamps and a high-efficiency magnetic ballast. Disadvantages of fluorescent lamps are: It’s hard and very costly to dim, size is bigger, not very easy to control optically, with toxic trace of mercury, noisier, emit radio interference, and emit more ultraviolet light than incandescent lamps.

Circular and Compact Fluorescent Lamps A Circular lamp is a standard fluorescent lamp tube that has been bent into a circle (as shown in the Figure below). Compact fluorescent lamps (CFLs), which are substantially smaller than standard fluorescent lamp were developed in the late 1970s and introduced to the U.S. market in the early 1980s.

Compact Fluorescent Lamps In a CFLs, the lamp tube is smaller in diameter and is bent into two to six sections (see the Figure on the previous slide). CFLs have much higher power densities per phosphor area than standard fluorescents, and their design was therefore dependent on the development of rare earth phosphors, which could hold up much better than standard phosphors at high power loadings.

Compact Fluorescent Lamps CFLs are available as both screw-in replacements for incandescent lamps and as pin-base lamps for hard-wired fixtures. They may be operated with separated ballasts or purchased as integral lamp/ballast units. On average, a CFL consumes only about one-third to one-fourth of the energy consumed by an incandescent lamp and has a lamp life up to 10 times longer. (The characteristics and application of CFLs are summarized in Table 12B.9) The lack of CFLs used in households is at least partially attributable to their limited availability in local supermarkets and hardware stores, their high price, and consumer uncertainty about how CFL watts and lumens correspond to the watts and lumens of a standard incandescent lamp. A lamp used with an electronic ballast is generally 20% more efficacious than a lamp used with a magnetic ballast. Introduction of dimmable CFL ballasts to the residential sector will allow the replacement of more incandescent lamps with CFLs.

Energy Recovery • The most frequently used heat-recovery luminaire draws air from the room across the tubes or lamps and delivers it to a plenum above the ceiling from where it can be passed to mix with the inlet air to the room. Less frequently water is used as the coolant fluid. • One point which must be taken into account when designing heat-recovery luminaires is that the efficacy of a typical fluorescent tube varies with the temperature of the tube surface. For example a typical fluorescent tube will give its maximum light output at a tube surface temperature of about 35oC; if the tube surface temperature is cooled to 20oC the light output will fall to about 75% of the maximum; similarly if the tube surface temperature is allowed to rise to 70oC the output will again be about 75% of the maximum.

Energy Recovery (Example II-2.1) An office is to be lit to a level of 500 lx with twin 68 W fluorescent tubes of 80 W electrical input with an efficacy of 60 lm/W. It is suggested that energy recovery luminaires could be used in which 75% of the output from each tube can be recovered. Estimate the total energy recovery possible from the office lighting, and the mass flow rate of air through each luminaire when the room air temperature is 20oC and the air entering the plenum is 28oC. The office floor area is 115 m2. Solution:

ISAT 413 ─ Module II: Lighting