Lighting
Why Is Lighting Important? Energy used for lighting constitutes a significant fraction of total building energy, sometimes more than HVAC. Inefficient lighting contributes to both power bill and cooling bill People notice lights and changes in lighting much more than, say, improvements in boiler efficiency.
Three Important Considerations for Lighting (1) When do the lights need to be on? (2) How much light is needed, and does light color matter? (3) What is the most efficient/economical type of lighting?
Lighting Measurements Visible light output (intensity) of a lamp is measured in lumens. Surface illumination (intensity per unit surface area), measured in footcandles (fc): fc = emitted lumens/surface area (ft 2 ) or lux = lumens/area (m 2 ) The efficiency (or efficacy) of a light fixture is measured in lumens/watt lumens of light output per watt of electric power input.
How Much Light Is Needed? Lighting standards published by the Illuminating Engineering Society (IES). ASHRAE lighting standards developed in conjunction with IES. Detailed information available from IES or ASHRAE. Sample tables provided in your textbook (Tables 5.4 and 5.5 of new edition). Lower values apply to people under 40, higher values to those over 55. Color rendition important for industrial tasks (wire color codes), for retail merchandizing, etc.
Iluminance Categories (see Table 5.5) Activity Category fc Public spaces, dark surroundings A 2/3/5 Orientation for short visit B 5/7.5/10 Work space, occasional task C 10/15/20 Visual task, high contrast, large D 20/30/50 Vis. task, med. contrast, small E 50/75/100 Vis. task, lo contr. or very small F 100/150/200 Long task, low contr, very small G 200/300/500 Brain Surgery! I 1000/1500/ 2000
Lighting for Specific Tasks Area/Activity Classrooms Conference rooms Drafting Lobbies Simple inspection Exacting inspection Machine shops Material handling Inactive storage Building entrance Illum. Category D to E D E to F C to D D H D to H C to D B A
When Is Light Needed Lighting is needed when the area is occupied or when needed for safety/security reasons, and no natural lighting is available. Lights in large areas can be wired in small groups so that only lights in the area occupied are switched on Reduce the span of the light switches to save energy.
Controlling Light Timing Often lights can be set to full power for normal activity and at a greatly reduced level for safety/ security when the room is unoccupied. Timer switches or infrared motion detector actuated switches can be used to insure that lights are on only when they are needed. Light level actuated switches can be used to insure that security lighting only works when it is dark and to turn off or dim electric lighting if sufficient daylight is available.
What Light Type Is Best? This is a complicated question- depends on activities occurring in the illuminated space and on lighting system maintenance. A light consists of a luminaire (fixture), often a ballast, and a lamp (or bulb), and performance of all three affects the lighting efficacy. Ballasts are used in fluorescent and high intensity discharge (HID) lights to provide correct voltage to lamp and to control starting characteristics. Ballasts consume 10 to 20 % as much energy as the light itself. Various efficiencies are available.
Luminaires Luminaire design has a big impact on overall efficacy. A poorly designed (or DIRTY) luminaire will absorb much of the emitted light before it gets to the surface where lighting is desired. Well designed luminaires are easy on the eye and allow useful application of most of the light emitted by the lamp by reflecting upward emitted light back downward.
3 Principal Light Types In order of increasing efficacy and cost: incandescent lamp (typical home lighting), resistance heated tungsten filament fluorescent lamp. Electric arc causes lamp s mercury vapor to emit UV from lamp, which strikes phosphor-coated wall, and energy is reemitted as visible light (lamp walls fluoresce). high intensity discharge lamps (HID) of various sorts: mercury vapor, metal halide and low- and high-pressure sodium lamps (factory, high-ceiling and outdoor lighting).
Fluorescent Light Operation
Incandescent Lamp Types
Recessed Incandescent Fixtures
Fluorescent Lamp Types
Open Fluorescent Fixture (Luminaire)
Shielded Fluorescent Fixture (Luminaire)
Troffer Tray Fluorescent Fixture (Luminaire)
Exit Light (Incandescent or Fluorescent) 2CFLs
Effect of Temperature on Fluorescent Lamp Output
HID Lamp Types
Typical HID Fixture
Incorrect HID Outside Area Lighting
Correct HID Outside Area Lighting
Color Rendition The color of an object in a lamp s light relative to its daylight color is the color rendition. The following table is extracted from Table 5.2 of new edition of text.
Color Rendition of Various Lamp Types (see Table 5.2) Cool White Multi- Incandescent Fluorescent Vapor Appearance on Yellowish White Greenish neutral surface white white Atmosphere Warm Neutral to cool Cool, greenish Colors stronger R, O, Y O, Y, B Y, G, B Colors grayed B R R Effect on Ruddiest Pale pink Grayed Complexions Remarks Good color Blends with Similar to rendering daylight, good Cool White color rendering
Light Degrades Over Time Light output tends to decrease over time for most lamp types. Figures show degradation of lamp output as a function of hours of use (called lumen maintenance). Lamp lumen decrease with time should be accounted for when designing lighting systems. Illumination levels are also degraded by the burnout of individual lamps, which is described by lamp mortality curves (see text).
Percent Lumens Incand. Lumen Maintenance 100 Percent of Rated Life
Fluoresc. Lumen Maintenance Percent Lumens Burning Hours
Percent Lumens HID Lumen Maintenance Burning Hours
Percent Surviving Incandescent Mortality 100 Percent of Rated Life
Fluorescent Mortality 100 Percent Surviving Percent of Rated Life
Combined Effect of Dirt and Lumen Lamp % Useful Light Lumen Loss Time (Fig. 5-12)
Lighting Maintenance Maintenance encompasses two factors: lamp replacement and cleaning. Illumination levels are degraded by dirty lamps, dirty fixtures and dirty reflective surfaces. Extent of degradation is given by tables such as those presented in text, samples of which follow. The luminaire maintenance category (see Table 5.6) and the degree of dirt conditions (see Table 5.7) must be identified to quantify lumen depreciation due to dirt.
Luminaire Dirt Depreciation Factors Fraction of Initial Light Output
Luminaire Dirt Depreciation Factors Category IV Fraction of Initial Light Output Months
Lamp Replacement Lamp replacement can be either by spot replacement of individual bulbs as they fail or by group relamping of all lamps in an area. Replacement costs are the sum of the bulb cost plus the labor cost of lamp replacement. The labor cost per lamp is significantly lower for group replacement than for spot replacement, but the bulb cost is somewhat higher because lamps are mostly replaced before they burn out. Often the net cost is lower for group relamping.
Lamp Replacement Economics (Figure 5-19 shows fluorescent lamp percent survival (yaxis) vs. percent of rated life)
Example Given: A 30 50 ft office now uses recessed ceiling PAR lighting having these characteristics: bulb life: 2000 hr Power: 150 W Initial lumens: 1900 Cost: $5/bulb 56 bulbs are now used with group bulb replacement at 1900 hours costing $120/replacement. Standards call for 50 fc of illumination for this application.
Example (Cont d) A project is considered to replace incandescent lighting with 2-bulb fluorescent fixtures costing $40 plus $30 installation labor each, plus $600 to disconnect and remove old fixtures, plus new fluorescent bulbs with these characteristics: bulb life: 20,000 hr Power: 32 W Initial lumens: 2975 Cost: $7/bulb The electronic ballasts in the fluorescent fixtures cause 10% more power consumption.
Example (Cont d) Fluorescent lights will be group replaced every 16,000 hrs at a labor cost of $200. New lights will be cleaned every year at a cost of $150. The office is clean and the luminaires have an opaque top enclosure and louvers for the bottom enclosure (Maintenance Class IV). Lights are operated 12 hr/day for 250 day/yr. Electricity costs 3.75 /kwh with a $6/kW monthly demand charge.
Example (Ongoing) Find: The simple payback period for replacing the incandescent lighting with fluorescent lighting.
Example (Cont d) Sol n: (1) Determine how many new bulbs and fixtures are required. Let s choose to achieve 50 fc just before bulbs are replaced, and assume average fixture dirtiness at the time of bulb replacement. The light output is: Output = Initial Lumens Age Factors Dirt Factor First determine the number of bulbs burning by examining the fluorescent mortality curve (Figure 5-16 of new textbook) for a percent of average life of 16,000/20,000 = 80%:
Fluorescent Mortality Percent Surviving Percent Surviving 83% 100 Percent of Rated Life
Example (Neverending??) Next we consider how brightly the still functional bulbs are burning at 16,000 hrs. The fluorescent lumen maintenance curve in our textbook (Figure 5-13) is for a bulb with a 12,000 hr life. Our bulb has a 20,000 hr life. A reasonable assumption is that the lumen maintenance will be the same for percent of bulb life. For the 12,000 hr bulb, 80 percent of bulb life is 9600 hrs. Examining Fig. 5-13 at 9600 hrs, and assuming average performance, the percent of initial lumens for the 20,000 hr bulb at 16,000 hours is approximately 78 percent.
Fluoresc. Lumen Maintenance Percent Lumens About 78% of initial lumens at 9600 hrs, or 80 % of average life. Burning Hours
Example (Cont d) Taking bulb mortality (83% survival) and lumen maintenance into account (78% of initial lumens), the age factor is: Age factor = 0.83 * 0.78 = 0.647 This means that if the fixtures were perfectly clean, the light output at 16,000 hours is only 65% of what it was when the bulbs were all new. But we are assuming that the fixtures have six months of dirt on them. Fixtures are Class IV maintenance under clean conditions:
Category IV Months Fraction of Initial Light Output
Example (Cont d (and just gettin warmed up)) The dirt depreciation factor is about 93%. At the time of bulb replacement, the percent of initial light output (dirt factor age factor) is: output = 0.93 0.647 = 0.60 or 60% We want to achieve an illumination of 50 fc at this time, where illumination = lumens/area. So, the total output lumens required at replacement is lumens = area illumination lumens = 30 ft * 50 ft * 50 fc * 1 lum/ft 2 /fc At lamp replacement time, need 75,000 lumens.
Example (Cont d) Next, if 60% of the original light output is available at the time of group lamp replacement, then the initial lumens needed is: Initial lumens = 75,000/0.6 = 125,000 lumens Then the number of bulbs needed is: N bulbs = 125,000 lum/2975 lum/bulb = 42 bulbs We will use 42 bulbs or 21 two-bulb fixtures. First Cost = 21 * ($40/fixture + $30/install) + $600 (remove old) + 42 * $7/bulb First Cost = $2364
Example (Still Cont d) Next, Annual Savings = Energy Savings + Bulb Replacement Savings. Energy Savings are the difference between old and new energy costs. Old Energy Cost: Use 56 bulbs @ 150W/bulb = 8.4 kw energy = 8.4 kw * 250 days * 12 hr/day * $0.0375 kw-hr = $945/yr Demand = 8.4 kw * $6 kw/mo * 12 mo/yr = $605/yr Old Energy Cost = 945 + 605 = $1550/yr
Example (Cont d) 10% extra for ballast New Energy Cost: 42 bulbs * 32 W/bulb * 1.1 = 1.48 kw energy = 1.48 kw * 250 days * 12 hr/day * $0.0375 kw-hr = $166/yr Demand = 1.48 kw * $6 kw/mo * 12 mo/yr = $107/yr New Energy Cost = 166 + 107 = $273/yr Energy Savings = 1550-273 = $1277/yr
Example (More Cont d) Replace Time Old Bulb Clean and Replace Costs: bulb-hr/yr = 250 * 12 hr/yr * 56 bulbs = 168,000 bulbs/yr = (168,000 bulb-hr/yr)/1900 hr = 88.4 replace cost = 88.4 bulb/yr * $5/bulb = $442/yr replace labor cost = (250 * 12 hr/yr)/1900 hr/repl * $120/repl = $189/yr Old Cost/yr = 442 + 189 = $631
Example (Still Cont d (almost done)) New Bulb Clean and Replace Costs: bulb-hr/yr = 250 * 12 hr/yr * 42 bulbs = 126,000 bulbs/yr = (126,000 bulb-hr/yr)/16,000 hr = 8 replace cost = 8 bulb/yr * $7/bulb = $56/yr replace labor cost = (250 * 12 hr/yr)/16,000 hr/repl * $200/repl = $38/yr cleaning cost = $150/yr New Cost/yr = 56 + 38 + 150 = $244/yr
Example (Grand Finale!) Clean and Replace Savings = 631-244 = $387 Total Annual Savings = 1277 (energy) + 387 = $1664/yr Simple Payback Period = 1st Cost/Annual Savings SPP = $2364/($1664/yr) = 1.4 years Excellent Investment!
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Lighting System Audit Examine the present system to determine the lighting type, wattage, location, degree of lumen depreciation, burned out lamps, luminaire and reflective surface dirt. Determine use and actual lighting needs of the each area, including lighting times, illumination levels and color rendition. Use forms such as that given by text Figs. 5-20 and 5-21.
Midnight Audit A "midnight audit" as described in text, is also useful to determine which lights are typically left burning that could be turned off. The assumption that certain lights are turned off at night may prove false!
Some Lighting ECOs Make sure lighting does not exceed visual task, safety and aesthetic needs. Reduce energy by adjusting illuminance to meet recommended levels. Relamping Delamping Group similar visual tasks together so excess lighting is avoided for some tasks because light requirements are high for adjacent tasks.
Lighting ECOs When possible, arrange for occupants working after hours to work in close proximity to one another. (ooh la la) Use light colors for walls, ceilings, furniture, etc., to increase utilization of light, and reduce lighting power to achieve required illuminances. Avoid glossy finishes to limit reflected glare. Use small switch spans and dimmers to allow flexible control of lighting.
Lighting ECOs Light building when occupied only, and when required for security or cleaning. Use occupancy and light level sensors for control. Use daylighting where and when it is available. Provide flexibility with shading so that daylighting can be maximized. Use daylighting in transition zones, lounge and recreational areas and where the variation in color, intensity and direction may be desirable.
Lighting ECOs Install lamps with highest efficacies to meet the light source color and distribution needs. Use T8 fluorescent and high-wattage compact fluorescent systems with electronic, energy efficient ballasts for better color and efficacy. Use high-efficacy metal halide and high-pressure sodium light sources for exterior floodlighting. Where incandescent sources are necessary, use reflector halogen lamps for increased efficacy. Use compact fluorescent lamps, where possible, to replace incandescent sources.
Lighting ECOs Select luminaires that do not collect dirt rapidly and can be easily cleaned. Clean luminaires and replace lamps on a regular maintenance schedule to ensure proper illuminance levels and low replacement costs. Adjust custodial service so that it occurs in daytime or, if at night, it occurs only in concentrated areas with remaining lights reduced.
Lighting ECOs Train personnel to turn off incandescent lamps promptly when space is not in use, fluorescent lamps if the space will not be used for 5 min or longer, and HID lamps (mercury, metal halide, high-pressure sodium) if the space will not be used for 30 min or longer. Restrict parking after hours to specific lots so lighting can be reduced to minimum security requirements in unused parking areas.