ISAT 413 ─ Module II: Lighting

1. ISAT 413 ─ Module II: Lighting Topic 3: Energy efficient lighting technologies and their applications (2) • The Design, Applications, and Efficacy of Various Lighting Technologies • Lamps (continued) • Ballasts • Lighting Fixtures and Controls • Efficient Lighting Operation • Current Production • The Cost-Effectiveness of Efficient Lighting Technologies • Example (Calculate Luminous Flux using EXCEL)

2. Lamps(continued) High-Intensity Discharge Lamps High intensity discharge(HID) lamps produce light by discharging an electrical arc through a mixture of gases. In contrast to fluorescent lamps, HID lamps use a compact “arc tube” in which both temperature and pressure are very high. Compared to a fluorescent lamp, the arc tube in an HID is small enough to permit compact reflector design with good light control. Consequently, HID lamps are both compact and powerful. There are currently three common types of HID lamps available: mercury vapor (MV), metal halide (MH), and high-pressure sodium (HPS). Figure at right shows MH (left) and HPS (right) HID lamps.

3. Characteristics of High-Intensity Discharge Lamps

4. Low-Pressure Sodium Lamps (SOX) A low-pressure sodium (LPS) lamp produces light by discharging an electrical arc through vaporized sodium.

5. Low-Pressure Sodium Lamps (continued) • In Low Pressure Sodium light has a number of very unique properties arising from this spectral output, many of which make it technically the most suitable light source for road lighting. But the monochromatic light makes it very difficult to discern the colour of cars, people’s clothing, and other objects. • In addition, the large physical size of the lamp means that it has a low luminance so it is less likely to give rise to glare, and the low operating temperature permits the use of compact optical systems and lightweight plastic lanterns.  They are the favoured light sources for tunnel illumination.  The long lamps may be aligned end-to-end to produce a continuous line of light and this almost totally eliminates the stroboscopic effect of driving past high brightness lights at speed.  Driver fatigue is drastically reduced there is a well proven link between low pressure sodium lighting and reduced accident rates in tunnels. Fluorescent lamps also lend themselves well to this application and are sometimes encountered, but SOX offers a longer-lived and more energy efficient solution.

6. New Developments in Efficient Lamps Electrodeless Induction Lamp In an induction lamp, the power supply converts ordinary 60 Hz current into radio-frequency power that is fed into an electrical coil. The coil excites a gas plasma inside the bulb, releasing UV radiation that strikes the rare earth phosphor coating of the bulb and is converted into visible light. • Its efficacy is about 50 LPW, CRI = 82, Color temperature is about 3,000 K. • It intends to replace 75-W incandescent reflector lamps in the commercial sector. • They cost approximately $20 per lamp.

7. New Developments in Efficient Lamps (continued) Sulfur Lamp The sulfur lamp is a very new high-intensity discharge source. The lamp’s system consists of a power source that feeds radio-frequency or microwave radiation to a small, rotating quartz sphere containing sulfur and a mixture of noble gases. The sulfur lamp is: • Full Spectrum, like the sun • Very Stable, both in color and brightness • Efficacy is about 80 to 100 LPW • Long-lived, with minimal service requirements • Environmentally safe, no mercury, just sulfur and argon • Quick to start, 100% in 25 seconds • Dimmable to 20%, and maintains color • Compact, when compared to other sources (see photo on the right)

8. Ballasts Because both fluorescent and HID (High Intensity Discharge) lamps have a low resistance to the flow of electric current once the discharge arc is struck, they require some type of device to limit current flow. A lamp ballast is an electrical device used to control the current provided to the lamp. In most discharge lamps, the ballast also provides the high voltage necessary to start the lamp. The most common types of ballasts are magnetic core-coil and electronic high-frequency ballasts (see Figure at right). • A magnetic core-coil ballast uses a transformer with a magnetic core coiled in copper or aluminum wire to control the current provided to a lamp. Magnetic ballasts use standard power of 60 Hz and operate at the same frequency.

9. Ballasts (continued) • An electronic high-frequency ballast uses electronic circuitry rather than magnetic components to control current. Electronic ballasts use standard 60 Hz power but operate lamps at a much higher frequency (20,000 to 60,000 Hz). Where there are two lamps per ballast, electronic ballast systems are approximately 20% more efficacious than magnetic ballast systems, where there is only one lamp per ballast, electronic ballast systems are almost 40% more efficacious than magnetic ballast systems. • The cathode cut-out (hybrid) ballast is a modified magnetic ballast. It uses an electronic circuit to remove the filament power after the discharge has been initiated for rapid-start lamps. Cathode cut-out ballasts use approximately 5 to 10% less energy than energy-efficient magnetic ballasts. • Almost all ballasts used for HID lamps are magnetic, and a number of different types are available. The various types differ primarily in how well they tolerate voltage swings and, in the case of HPS lamps, the increased voltage required to operate the lamp as it ages.

10. Lighting Fixtures A lighting fixture is a housing for securing lamp(s) and for controlling light distribution to a specific area. The function of the fixture is to distribute light to the desired area without causing glare or discomfort. The distribution of the light is determined by the geometric design of the fixture as well as the material of which the reflector and/or lens is made. The more efficient a fixture is, the more light it emits from the lamp(s) within it. Although a lighting fixture is sometimes referred to as luminaire, the term “luminaire” is most commonly used to refer to a complete lighting system including a lamp, ballast, and fixture. • Types of fluorescent lighting fixture that are commonly used in the nonresidential sectors include recessed troffers, pendant-mounted indirect fixtures and indirect/direct fixtures, and surface-mounted commercial fixtures such as wraparound, strip, and industrial fixtures. • Most offices are equipped with recessed troffers, which are direct (downward) fixtures and emphasize horizontal surface. • A direct/indirect fixture is suspended from the ceiling and provides direct light as well as indirect.

11. Lighting Fixtures (continued) • A wraparound fixture has a prismatic lens that wraps around the bottom and sides of the lamp, and is always surface-mounted rather than recessed. Wraparound fixtures are less expensive than other commercial fixtures and are typically used in areas where lighting control and distribution are not a priority. • Strip and industrial fixtures are even less expensive, and are typically used in place where light distribution is less important such as grocery stores. • The most common incandescent fixture in the nonresidential sector is the downlight fixtures in area where lighting control is less critical. • Ways to improve the efficiency of fluorescent lighting fixtures include: • Use specular reflector fixtures, reflective materials such as anodized aluminum, silver, and multiple dielectric coating are used to improve reflectivity and reduce reflection within the fixture. • The addition of vents to fixtures and thermal bridging are among the strategies being used to decrease the minimum temperature of the lamp wall.

12. Lighting Controls Control systems range from simple mechanical clocks to sophisticated building energy management systems that control the lighting in a building as well as the heating, ventilation, and air conditioning systems (HVAC). Lighting control systems include programmable timers, occupancy sensors, daylighting controls, lumen maintenance control, and dimmers for incandescent and compact fluorescent lamps. Of the control systems available today, integrated workstation sensors and energy management systems are two of the most promising efficiency options. • An integrated workstation sensor allows users to control lighting, electric heating and cooling equipment, and other electrical equipment (such as plug loads) for individual workstations or space. • Comprehensive, automated, building energy management systems are user-programmable and can control equipment for several energy end uses including lighting, HVAC, security, and safety systems.

13. Efficient Lighting Operation In addition to high-quality design and the use of efficient lighting technologies, commissioning and maintenance of lighting systems play important roles in maximizing energy savings. • In a very dirty environment, light output can be reduced by 50% in less than 2 years. Thus, cleaning not only makes the lighting system and room look better, it also increases the efficiency of the lighting system. • Group relamping (replacing all lamps in an area or building simultaneously rather than as each lamp burns out) is another strategy for maintaining high-efficiency fluorescent and HID lighting systems and often saves time and money as well. Group relamping is usually done when the lamps are operated for 60 to 80% of their rated lifetimes. Even though the lamps are retired before the end of their useful lives, early relamping can greatly reduce the amount of initial overdesign that is necessary and results in a more efficient lighting system. Compared to the high cost of having a person replace one lamp at a time, group relamping can often result in substantial labor cost savings.

14. Current Production • In contrast to the concentrated (by only a few firms) markets for lamps, ballasts, and fixtures, there are many firms involved in the lighting controls market. • The growth in total incandescent lamp shipments closely matched the growth in the number of households between 1974 and 1993. Shipments of fluorescent and high-intensity discharge lamps have increased faster than the growth in population, number of households, and commercial floorspace. • Like the lamp market, the ballast market has evolved considerably in recent years. Electronic ballasts account for leas than 3% of total ballast sales in 1987 but more than one-third of totals by 1993. Ultimately, electronic ballasts are expected to replace magnetic ballasts for many fluorescent lighting applications. The dramatic increase in sale of electronic ballasts in recent years has been accompanied by a significant decrease in price.

15. The Cost-Effectiveness of Efficient Lighting Technologies • The use of cost-effective design practices and lighting technologies could reduce the energy consumption in the U.S. for commercial interior lighting by 50 to 60% and reduce the energy consumed by residential interior and exterior lighting by 20 to 35%. However, consumer choices regarding what types of efficient lighting technologies to purchase depend not only on the reliability, lighting quality, and energy-saving potential of the alternative system, but also on the additional cost of the more efficient technologies. • In addition to the cost of equipment and installation, one should consider energy, relamping, and maintenance costs over the life of the lighting system, as well as disposal costs. • Lighting is an important electrical end use in all sectors and building types in the U.S., and counts for approximately one-fifth of national electricity use. Through the use of more efficient lighting technologies as well as advanced lighting design practices and control strategies, there is significant potential for saving electricity, reducing consumer energy costs, and reducing the emission of greenhouse gases associated with electricity production.

16. Spectral Luminous Efficiency The human eye is not uniformly sensitive to all wavelengths of the visible spectrum, and the Spectral Luminous Efficiency curve, shown below, and denoted V(), demonstrates how the sensitivity of the eye varies with wavelength. This curve is for a “CIE standard observer,” each individual’s sensitivity will differ somewhat. V() is for photopic vision, which is shown to peak at 555 nm. Only part of the radiant energy from a blackbody or a real radiator contributes to the sensation of vision, the energy must be in the visible spectrum, and is weighted by the sensitivity of the eye. The luminous flux, v, is a measure of the visual response associated with the radiant flux, e. The lumen (lm) is the unit of luminous flux, where one lumen of luminous flux is associated with a radiant flux of 1/683 Wata wavelength of 555 nm.

17. Spectral Luminous Efficiency (continued) Thus if e() is the spectral radiant flux as a function of wavelength, where, c velocity of light in vacuum = 3.0108 m/s, h  Planck’s constant = 6.62610-34 J.s, k  Boltzmann’s constant = 1.3810-23 J/K, T is absolute temperature (K) of the blackbody, and  is the wavelength in meters, then the associated luminous flux and total luminous flux, calculated by integration, are given below.

18. Calculation of Radiant and Luminous Fluxes (Example II-3.1) A standard 60-watt incandescent lamp operates with a filament temperature of 2790 K. a). If the lamp produces 855 lumens, what is its efficacy? b). Use the Stefan-Boltzmann law to determine the surface area of a blackbody at 2790 K that emits a radiant flux of 60 W. c). Develop a spreadsheet that calculates the radiant flux from a blackbody by numerically integrating Planck’s equation with surface area and temperature as parameters. Test your spreadsheet by using the area found in Part (b) to calculate the radiant flux at 2790 K. You may assume that wavelengths below 200 nm and above 50 mm make negligible contributions to the radiant flux. d). Modify your spreadsheet so that it also calculates the luminous flux of a blackbody (collect spectral luminous efficiency data from HW_2_Luminous_efficiency.xls on ISAT 413 “Blackboard/ Assignments/ Week 2/ HW_2_Assignment” site). Compare the luminous flux to the radiant flux to determine the theoretical efficacy of a blackbody operating at 2790 K. Account for any differences with Part (a). e). Suppose that a blackbody could be modified to emit radiant energy only in the visible spectrum and that its spectral power distribution is given by Planck’s equation. What would be the maximum theoretical efficacy of the modified blackbody?

19. Solution (Hints):

20. Solution (Hints continued): f ). Ways to improve the efficacy of incandescent lamps: