Light Sources - Comprehensive Notes

Objectives

  • Identify and classify different types of light sources (natural and artificial) used in building utilities.
  • Analyze the energy efficiency of various lighting systems and their impact on building sustainability.
  • Evaluate the psychological and physiological effects of different light sources on building occupants.
  • Examine the principles of lighting design in relation to functionality, aesthetics, and safety.

Light Sources

  • Electric lighting began around 1870 with arc lamps and gained momentum with Thomas Edison’s incandescent lamp in 1879.
  • Today's electric light sources have 3 generic classifications: Incandescent Lamps, Fluorescent Lamps, High-Intensity Discharge (HID) Lamps
  • Thomas Alva Edison: a prolific inventor who significantly influenced modern life with inventions like the incandescent light bulb and contributions to the telegraph and telephone.

Efficacy of Light Sources

  • Efficacy: measured in lumens per watt (lm/W), indicates the efficiency of a light source.
  • Efficacy generally increases with wattage, making higher-wattage lamps more energy-economical.
  • Electric lighting in nonresidential buildings consumes 25-60% of electric energy, emphasizing the importance of integrating daylight.

Types of Lighting

  • Artificial Lighting
    • Provides consistent and easily controlled visual environments.
    • Has minimal impact on architectural aesthetics.
    • Historically, cheap electricity led to ignoring daylight in designs.
  • Daylighting
    • Daylight is variable and can cause glare, direct sunlight issues, and heat gain.
    • When properly utilized, daylight reduces energy consumption and enhances visual performance.

PSALI Technique

  • British Approach: Emphasizes daylight as the primary lighting source, with artificial lighting as a supplement.
  • PSALI (Permanent Supplementary Artificial Lighting in Interiors)
  • Residences are occupied during nighttime when daylight is unavailable, requiring artificial lighting systems to meet full lighting needs.
  • Other structures in Night Use rely entirely on artificial lighting.

Characteristics of Daylight

  • Variability: The most prominent characteristic of daylight.
  • Factors affecting exterior illumination:
    • Altitude and azimuth (latitude, date, time of day)
    • Weather conditions (cloud cover, smog)
    • Effects of local terrain (obstructions and reflections)
  • Design Considerations:
    • Location-specific or general weather-based calculations?
    • Accounting for daily and seasonal sunlight changes?
    • Required level of accuracy?

Sky Conditions

  • Four basic sky conditions for calculations:
    • Completely overcast sky
    • Clear sky, without sun
    • Clear sky, with sun
    • Partly cloudy sky

Factors in Interior Daylighting

  • Horizontal & Vertical Surfaces
    • Daylight entry through side windows influences interior lighting.
    • Vertical component affects horizontal surfaces; horizontal component impacts vertical ones.
    • High windows optimize lighting for horizontal tasks; lower windows suit vertical tasks.
    • Tall, narrow windows allow deeper daylight penetration, enhancing illumination.
  • Windows Details
    • Narrow mullions and light metal frames can block 8-10% of the total fenestration area, while larger supports and smaller glass panels further reduce daylight entry.
    • Dust accumulation diminishes light transmission.
    • Wired glass, though beneficial for safety, obstructs daylight.
    • Pipes, ducts, and mechanical systems near windows can further block natural light.
  • Surface Reflections
    • Use high-reflectance materials at the back of rooms to improve illumination.
    • Optimize building orientation and install sun control devices—vertical for low sun angles, horizontal for high angles.
    • Translucent fenestration balances daylight and glare.
    • Tinted windows and heat-reflective films help regulate light and temperature.
  • Glare and Heat Control
    • Position furniture to avoid direct glare and mitigate reflections from adjacent structures using shading or vegetation.
    • IRC (Infrared Cutoff) reduces glare and improves light distribution.
    • Floors need 20% reflectance, while walls require 50% for optimal eye adaptation.
    • Reflective exterior surfaces (50-70%) enhance daylight penetration, and combining them with high-reflectance ceilings maximizes interior illumination.

Incandescent Lights

  • An incandescent light produces light by heating a tungsten filament to a high temperature until it glows, enclosed in a glass bulb filled with inert gas to prevent oxidation.

Typical Incandescent Lamp Parts

  • glass bulb
  • filament
  • support wire
  • gas fill
  • lead-in wire
  • button
  • pinch
  • feedthrough
  • exhaust tube
  • stem tube
  • fuse
  • base

Lamp Bulb Shape

  • Shapes impact light distribution, fixture compatibility, and efficiency.
  • Elongated shapes provide uniform illumination for large spaces, while compact designs suit focused or decorative lighting.
  • To diffuse light, bulbs are typically either inside-frosted or coated with white silica.
  • Silica coatings ensure almost complete diffusion but slightly reduce output (2-3%), while inside-frosted bulbs offer partial diffusion without light loss.
  • General-use bulbs are often inside-frosted, with colored options available through coated glass or colored glass designs.

Lamp Base

  • The lamp base serves as the connection point between the bulb and the socket, enabling access to the electric current.
  • Most lamps utilize screw bases of varying sizes, with the medium screw base being the most common.
  • High-wattage general service lamps (300 W and above) often use mogul screw bases due to their robust design.
  • For applications requiring precise filament positioning, specialized bases are used instead of screw bases to ensure accuracy and optimal performance.

Operating Characteristics

  • Burning a 120-V lamp at 125V (104.2%) means approximately:
    • 16% more light (lumens)
    • 7% more power consumption (watts)
    • 8% higher efficacy (lumens per watt)
    • 42% less life (hours)
  • Burning a 120-V lamp at 115V (95.8%) means approximately:
    • 15% less light (lumens)
    • 7% less power consumption (watts)
    • 8% lower efficacy (lumens per watt)
    • 72% more life (hours)
  • Operating lamps at their rated voltage is ideal to achieve a balance between output, efficiency, and lifespan.
  • A detailed cost analysis should be conducted for specific installations, considering factors like energy costs, re-lamping schedules, and fixture accessibility.

Incandescent Lamp Characteristics

  • Lumen Maintenance: Light output decreases slowly with lamp life as the bulb blackens. Position during burning and bulb temperature affect this characteristic.
  • Color: White, with a large, yellow-red component, flattering to the skin. Color depends on temperature; high-voltage lamps are bluer, low-wattage lamps are yellower. Dimmed lamps give yellow-red light.
  • Lamp Efficiency: Efficiency increases with wattage, varying from 8% for a 25W lamp to 13% for a 1000-W unit. A 100-W lamp produces the same 1750 lm as two 60-W lamps, representing a 20% increase in efficacy.
  • Surroundings: Generally impervious to external heat, cold, or humidity. Starting completely unaffected.

Incandescent Lights - Advantages

  • Low cost and simple installation without additional accessories.
  • Instant start/restart and inexpensive dimming capabilities.
  • Compact fixtures with high focusability due to the point-source characteristic.
  • High power factor and a lifespan independent of the number of starts.
  • Good color rendering capabilities.

Incandescent Lights - Disadvantages

  • Low Efficacy, resulting in higher energy use, more fixtures, and increased heat gain.
  • Short lamp life, leading to frequent replacements and higher labor costs
  • Voltage sensitivity, requiring precise and sometimes costly circuit design.
  • Light concentration at the filament can cause glare or sharp shadows if fixtures are poorly designed.

Incandescent Lights - Applications

  • Infrequent or short-duration usage.
  • Situations requiring low-cost dimming.
  • Where the point-source property is essential, e.g., focusing fixtures.
  • Projects with minimal initial cost requirements.

Special Incandescent Lamps

  • Reflector Lamps
  • Interference (Dichroic) Filters
  • Low-Voltage Lamps
  • Krypton Gas
  • Energy-Saving Lamps
  • Tungsten-Halogen Lamps

Special Incandescent Lamps - Rough Service and Vibration Lamps

  • Designed to endure rough handling and continuous vibrations, which are harsh on general service lamp filaments.
  • While durable, their efficacy is lower than general service lamps.
  • Neither type is meant for general use.

Special Incandescent Lamps - Extended Service Lamps

  • Designed for 2500-hr life and are useful in locations where maintenance is irregular and/or re-lamping is difficult.
  • The lamp is really designed for slightly higher voltage than that at which it is applied, and therefore efficacy is reduced.
  • "Long-Life" lamps, which are guaranteed to burn for two, three, or five years, are lamps designed for much higher voltages than that at which they operate. Since they normally sell at a high cost and are very inefficient, their use is seldom advisable.
  • In a cost comparison made of three lamps with 750, 2500, and 10,000-hr lives, respectively, including cost of lamps, energy and re-lamping, the relative costs per million lumen hours were 1.0, 0.94, and 1.17, respectively.

Special Incandescent Lamps - Reflector Lamps

  • Made in "R" and "PAR" shapes and contain a reflective coating on the inside of the glass envelope; this gives the entire lamp accurate light beam control.
  • Both types are available in narrow or wide beam design, commonly called spot and flood, respectively.
  • R lamps are generally made in soft glass envelopes for indoor use, whereas PAR lamps are hard glass, suitable for exterior application.
  • Also available is a lamp with an elliptical reflector bulb shape. This causes the beam to focus a few inches in front of the lamp, permitting high-efficiency application in pinhole downlights or deep baffle units where use of ordinary R lamps causes trapping and loss of the most of the lamp's output.

Special Incandescent Lamps - Interference (Dichroic) Filters

  • Filters had been previously used only in specialized applications such as projection lamps to remove heat from the light beam, are now available in PAR lamps.
  • The basic filter is a thin film that operates on the interference principle rather than absorption. Thus, the surface remains relatively cool.
  • In one design that is utilized to limit the heat in the light beam, the film is applied to the inside back of the lamp. It acts by transmitting infrared heat out of the lamp back while reflecting light out the lamp front.
  • Typical applications are now window displays, over food counters, and in any location where a "cool beam" is desirable. Of course, provision must be made for removal of the heat from fixture if the lamp is housed.
  • In a second design, multiple-layer filters are applied to the front of the lamp. Each film acts to transmit one color and reflect its complement (two color, hence dichroic). These dichroic filter lamps produce a purer, more saturated color at high efficacy than is possible with selective absorption filters.

Special Incandescent Lamps - Low-Voltage Lamps

  • These lamps, in PAR shape and for 6-V operation, are available in extremely narrow beam spread (5-10 °} for special precision control floodlighting. The low voltage makes their application to exterior work simpler.

Special Incandescent Lamps - Krypton Gas

  • This gas in lamps in place of the usual nitrogen-argon mixture conducts heat more slowly from the filament and results in the approximately 10% higher efficacy, longer life, and a smaller envelope.
  • The cost premium for krypton lamps is approximately 50%.
  • Applications are in long-life lamps to increase efficacy and in exterior spots and floods to increase life and output.

Special Incandescent Lamps - Energy-Saving Lamps

  • These are basically long-life lamps that are filled with krypton to raise efficacy.
  • These lamps can be substituted for standard lamps for appreciable savings in energy costs and re-lamping costs.
  • Note that efficacy is still considerably below that of a standard lamp.
  • The use of krypton-filled lamps increases initial cost and decreases energy cost.

Special Incandescent Lamps - Tungsten-Halogen (Quartz) Lamp

  • This is a "gas filled tungsten incandescent lamp containing a certain proportion of halogens.” The halogens are iodine, chlorine, bromine, and fluorine. Thus, the quartz-iodine-tungsten filament lamp is a member of this class.
  • The lamp is basically an incandescent lamp, producing light and heat from the incandescence of its coiled filament.
  • Unlike the normal inert gas-filled incandescent lamp. the lamp envelope, which Is quartz to withstand high temperature, is filled with an iodine vapor that prevents the evaporation of the tungsten filament. This evaporation is what normally occurs in the incandescent lamp, resulting in the blackening of the bulb, light output deterioration, and eventual burnout.
  • Although the lamp has approximately the same efficacy as an equivalent normal incandescent, it has the advantages of longer life, low lumen depreciation (98% output at 90% life). and-a smaller envelope for a given wattage.

Special Incandescent Lamps - Tungsten-Halogen (Quartz) Typical Data

  • Typical Data for Quartz Tungsten-Halogen Lamps, Par, Reflector, and Tubular.
  • 120-v Lamps for Spol, Flood, and General Lighting
  • Includes information such as Watts, Bulb Type, Maximum Overall Length (Inches), Base Type, Rated Life (Hours), Beam Type, Approximate Initial Lumens, and Mean Lumens Through Life (Percentage).

Fluorescent Lamps

  • Fluorescent lamps are electric light sources that produce visible light by using electricity to excite mercury vapor. The excited mercury atoms emit ultraviolet (UV) light, which then strikes a phosphor coating on the inside of the lamp, causing it to glow and produce visible light.

Construction of Fluorescent Lamps

  • Fluorescent lamps, first widely introduced in 1937, have nearly replaced incandescent lamps in most applications, except for specialty lighting and residential use.
  • Comprised of a cylindrical glass tube, sealed at both ends.
  • Contains a mixture of argon (inert gas) and low-pressure mercury vapor.
  • Each end of the tube houses a cathode, which generates electrons necessary for starting and maintaining the mercury arc (gaseous discharge).
  • The mercury arc produces short-wave ultraviolet light.
  • The inside of the tube is coated with phosphors, which fluoresce (emit visible light) when exposed to the ultraviolet light.
  • The specific phosphor mixture used determines the spectral quality or color of the visible light output.

Preheat Lamps

  • The circuit includes a starter, a small cylindrical device plugged into a preheat fixture.
  • When the lamp circuit closes:
    • the starter energizes the cathodes;
    • after a 2-5 second delay, it initiates a high-voltage arc across the lamp to start it.
  • Automatic Starters: typically used, though desk lamps may require manual starting via a button that preheats the cathodes and triggers the arc upon release.
  • All preheat lamps use a bipin base for connection.
  • Wattages range from 4W to 90W, with lengths from 6 to 90 inches (0.15 to 2.25 meters).
  • Example of ordering abbreviations: F15T12WW
    • Fluorescent lamp
    • 5W power rating
    • Tubular bulb shape
    • 12/8-inch diameter (or 1.5 inches)
    • Warm white color
  • Preheat lamps are largely replaced by rapid-start and instant-start fluorescent types, which offer faster, more efficient operation.

Rapid-Start Lamps

  • Preheat lamps and Rapid -start lamps both share a similar build but differ in their circuitry.
  • Rapid-start circuitry eliminates the delay seen in preheat circuits by keeping the cathodes constantly energized (preheated).
  • When powered, the arc is struck immediately, without the need for an external starter.
  • Rapid-start lamps can function in a preheat circuit due to their similar operation.
  • However, preheat lamps cannot operate in a rapid-start circuit, as their cathodes require more current than rapid-start ballasts can supply.
  • Most Popular Lamp: the 40-W T-12 lamp is widely favored: Example: F40T12WW/RS (Fluorescent lamp, 40 watts, Tubular shape, Warm white color, Rapid start technology).
  • Standard operation: 425 milliamperes (mA)
  • Increased current raises light output.

Rapid-Start Lamps - Specialized High-Output Variants

  • High Output (HO): Operates at 800 mA
  • Very High Output (VHO): Operates at 1500 mA (1.5 amps). Manufacturers may refer to these as “super-high output” or “1500- mA rapid start”.
  • Power Groove Lamp: Operates at 500 mA; Features a unique grooved or dented glass tube design for enhanced efficiency.
  • All high-output lamps use double contact bases and require special ballasts for proper operation.

Rapid-Start Lamps - Applications

  • These lamps are ideal where high light output from compact sources is needed, such as:
    • Outdoor sign lighting
    • Street lighting
    • Merchandise displays
  • Due to significant heat generation, VHO lamps are often operated without enclosing fixtures to manage heat dissipation effectively.

Rapid-Start Lamps - Efficiency and Lifespan

  • HO and VHO lamps are:
    • Slightly less efficient than standard 425- mA rapid-start lamps.
    • Shorter-lived, making them less ideal for long-term or cost- sensitive installations.
  • Ordering and Identifications (Example: F72T12/CW/HO):
    • Fluorescent Lamp
    • 72 inches in length
    • T12 bulb shape
    • Cool white color
    • High output (1500 mA)

Instant-Start Fluorescent Lamps

  • Slimline lamps utilize a high-voltage transformer to ignite the arc, eliminating the need for cathode preheating.
  • Each end of the lamp is equipped with a single pin, which also functions as a switch.
  • The single pin design interrupts the ballast circuit when the lamp is removed, significantly reducing the risk of electric shock.
  • Operate in two-lamp circuits at currents of 200 mA or 425 mA.
  • Standard lengths range from 24 to 96 inches (0.60 to 2.40 meters).
  • These are hot cathode instant-start lamps, unlike high- voltage cold cathode lamps; they ignite without cathode preheating, using a high- voltage arc.
  • Can operate effectively at lower ambient temperatures (below 50 degrees F), making them ideal for outdoor applications.
  • Manufactured in certain sizes and currents not available in rapid-start lamps (e.g., 96 inches at 430 mA).
  • More expensive than rapid-start lamps.
  • Slightly less efficient, with higher costs for lamps and ballasts.

Instant-Start Fluorescent Lamps - Slimline

  • Ordering Description: For example: F42T6CW Slimline
    • F42: Fluorescent lamp, 42 inches in length
    • T6: Tubular shape with a diameter of 6/8 inch (narrow tube, 200mA)
    • CW: Cool white color
    • "Slimline” indicates instant-start functionality.
  • For instant-start lamps, the number after “F” refers to length, not wattage. This applies to lamps operating at currents other than the standard 425 mA.

Cold Cathode Tubes

  • Thimble-Shaped Cathode: Utilizes a large cathode and a high-voltage transformer to tear electrons from the cathode and ignite the arc.
  • Exceptionally long life, unaffected by the number of starts, which distinguishes them from hot cathode lamps.
  • Lower overall efficiency compared to hot cathode types, making them less suited for general lighting fixtures.
  • Easily dimmable and perform reliably across varying ambient temperatures.
  • Ideal for long continuous runs, such as:
    • Architectural lighting
    • Specialty lighting applications
  • Less commonly used for standard fixtures due to their specific design and operational focus.

Characteristics and Operations of Fluorescent Lamps

  • Lamp Life:
    • Lamp life data is typically based on a 3-hour burning cycle per start
    • The listed life expectancy represents the average life of a group of lamps, meaning half of the lamps in any group will have burned out by this time.
    • Burning hours per start directly influence lamp mortality rates. Longer cycles generally extend the lifespan of fluorescent lamps, whereas shorter cycles increase wear.
    • Fluorescent lamps should be turned off in areas unused for 15 minutes or more.
    • Takes into consideration:
      • Energy savings
      • Resource cost to replace lamps due to reduced life span from frequent switching.
  • Lumen Output:
    • During the first 100 hours of operation, fluorescent tubes experience a rapid decline in lumen output.
    • Beyond this initial period, the reduction in output slows significantly.
  • Efficacy:
    • Standard lamps range from 40–85 lumens per watt (lpw), accounting for ballast losses.
    • Ballast losses, which make up 5–12% of lamp wattage, are critical to include in calculations, as neglecting them would result in misleadingly high efficacy figures.
    • Standard 425-mA lamps are the most efficient; followed by HO 800-mA lamps, and then VHO 1500- mA lamps.
  • Temperature:
    • The light output of fluorescent lamps is directly affected by the ambient temperature around the tube.
    • Maximum efficiency occurs when the tube operates within a bulb temperature of 100 to 200 °F.
    • Output reduction occurs if temperatures deviate above or below this range.
  • Voltage:
    • Fluorescent lamp life is negatively affected by deviations from the rated voltage, differing from the relative resilience of incandescent lamps to low voltage.
    • Normal Voltage Ranges:
      • 120-V circuits: 110 to 125 volts.
      • 208-V circuits: 200 to 215 volts.
      • 277-V circuits: 250 to 290 volts.
  • Dimming and Low-Output:
    • Achieved using special one- or two-lamp ballasts with appropriate dimming controls.
    • Solid-state electronic dimming enables smooth dimming down to 1% output, with the ability to start the lamp at any light level.
    • Dimming equipment is relatively expensive and is typically justified only when smooth transitions and precise light level control are necessary.

Special Fluorescent Lamps

  • “U”-Shaped Lamps
    • Developed to answer the need for a high-efficiency fluorescent source that could be utilized in a square fixture, since the normal fluorescent lamp shape is frequently not architecturally suitable.
  • Reflector and Aperture Lamps
    • These lamps contain an internal reflector that performs in the same fashion as the more common reflector in the incandescent Rand PAR lamp. The reflector lamp is completely phosphor-coated, while the aperture lamp has a clear "window" resulting in very high luminance of this slot.
    • Both types have lower efficacy than a normal tube and are generally applied where an enclosing fixture is uneconomical or impractical. as in handrails or for sign illumination.
    • Tests using 235° reflector lamps in normal fluorescent fixtures intended for standard tubes indicate that the fixture coefficient of utilization increases up to 50%, depending on the fixture design. This is because the light normally trapped between the tubes and the fixture is saved, since almost no light is radiated above 62. 5c from the vertical (cut-ofF of the internal reflector).
    • Using reflector lamps for general illumination can result in considerable savings in energy costs.
  • Energy-Conserving Lamps
    • These lamps are produced by all three major manufacturers and have trademark names.
      • WATT-miser by General Electric
      • Econo-watt by Westinghouse
      • Super-saver by Sylvania

Special Fluorescent Lamps - Energy-Conserving Lamps

  • These lamps are intended as lower-wattage replacements for standard lamps.
  • Energy-saving lamps have higher efficacy compared to standard counterparts, meaning they consume less power for similar light output. Their light output is lower, and their lifespan is shorter, except for the 40 watt unit, which performs comparably to standard lamps.
  • Best suited for areas where direct substitution with reduced lighting levels is acceptable, such as:
    • Stores
    • Corridors
    • Walkways
    • Offices
  • Energy-saving lamps are clearly labeled by manufacturers to differentiate them from standard lamps.

Neon Lamps

  • Neon lamps use exhausted glass tubes filled with neon gas, which becomes ionized to conduct electricity.
  • These lamps require high voltage due to the large voltage drop at the cathode.
  • Transformers are essential to step up standard voltage (115 V) to 6,000 10,000 V, enabling proper lamp operation.
  • The emitted light ranges from pink to dark red, depending on the gas pressure. Additional colors can be achieved by mixing gases or using colored glass tubing.
  • Primarily used for street signs, window displays, and indoor signage, due to their bright and distinctive appearance.

High-Intensity Discharge (HID) Lamps - Characteristics

  • Mercury Lamps: Operate by passing an arc through high-pressure mercury vapor in a quartz or glass arc tube.
    • Produces light in the ultraviolet (UV) and visible regions (blue-green band).
    • This color is characteristic of the clear mercury lamp.

High-Intensity Discharge (HID) Lamps - Mercury Lamps

  • Lamp Designations
    • The simplified code adopted by the American National Standards Institute (ANSI) provides a standardized way to describe lamps across manufacturers. Here's a breakdown of the example provided, H38MP100DX:
      • H: Indicates the lamp type, in this case, a mercury lamp.
      • 38: Represents the ballast number, which specifies the compatible ballast for the lamp.
      • MP: Describes the lamp's physical characteristics, such as shape, size, or operational features.
      • 100: Denotes the lamp wattage, showing that this lamp operates at 100 watts.
      • DX: Identifies additional features like phosphor, glass coating, or coloring
  • Lamp Life
    • Mercury lamps have an extremely long average lifespan of 24,000 hours, based on 10 burning hours per start.
    • They are designed for long burning cycles, making them unsuitable for applications requiring frequent switching.
    • Life is affected by ambient temperature, line voltage and ballast design.
    • Mercury lamps are less sensitive to short burning cycles than fluorescent lamps.
    • However, they experience accelerated lumen depreciation as they near the end of their lifespan, prompting replacement before complete burnout.
  • Color Correction and Efficacy:
    • These are added because the blue-green light distorts almost all colors. The outer bulb is coated with phosphors that are excited by the UV light and are reradiated generally in the red band, which is entirely absent in the basic lamp color.
    • Depending on the arc tube design and the phosphors used, the color of the emitted light can be corrected to make it acceptable for general indoor use. Lamps are available in clear, white. color-corrected, and white-deluxe, in ascending order of color improvement. The deluxe lamp also uses a strain on the envelope to filter out some of the blue-green, which obviously reduces lamp output.
  • Ballast
    • Ballasts are required, as with all arc discharge lamps, to start the lamp and thereafter to control the arc. The basic ballast is simply a reactor that controls the arc after the discharge has been initiated. Three to six minutes are required for the lamp to reach full output since heat must be generated by electron flow to vaporize the mercury in the arc tube before the arc will strike. Once extinguished, the lamp must cool and the pressure must be reduced before restrike is possible. This restart delay amounts to 3 to 8 min., depending on the ballast type, and is an important consideration in design.
  • Dimming
    • Dimming of mercury tamps is possible and entirely practicable with the use of dimming ballast and solid-state dimming control. These are available for 400-. 700-, and 1000- W units and, unlike the case of fluorescents, dimming is a desirable and economical control means. Mercury tamps have so large an output that shutting off a unit creates an imbalance in the lighting - coverage - a problem readily solved by dimming.
    • A little used but very effective and economical output reduction technique is simply to change the circuit capacitance by an amount, depending on lamp size and ballast type. By doing this, the lamp wattage and output can be reduced by approximately 50% with no deleterious effect on lamp or ballast. This technique is by far the cheapest method of accomplishing an overall, even reduction in output
  • Application
    • Mercury-vapor lamps are applicable to indoor and outdoor use with proper attention to color and fixture brightness. Indoor application is generally limited to mounting 10 AFF or higher to avoid glare problems and to permit adequate area coverage. Use in industrial spaces and stores is common.

High-Intensity Discharge (HID) Lamps - Metal Halide Lamps

  • Modified by adding metal halides (e.g., salts of thallium, indium, or sodium) to the arc tube.
  • The metal halides radiate light at additional frequencies beyond the basic mercury spectrum.
  • Produces a warmer light compared to traditional mercury lamps.
  • Reduced lifespan and lumen maintenance, with only 60% of initial brightness retained at two-thirds of the lamp’s life

High-Intensity Discharge (HID) Lamps - High-Pressure Sodium (HPS) Lamps

  • While they operate as arc discharge units, their efficiency and distinct yellowtinted light derive from the spectral absorption phenomenon of high -pressure sodium vapor.
  • This process results in a color that closely resembles warm white fluorescent lamps.
  • Characteristics:
    • High Luminous Efficacy: Superior lumens per watt performance.
    • Yellow -Tinted Light: Ideal for outdoor applications, such as street and area lighting.
    • Durable Design: Long lifespan with reliable performance under varying environmental conditions.
    • Compact Arc Tube: Enables efficient energy transfer and stable operation.
  • HPS lamps are not voltage-sensitive, ensuring more stable performance compared to metal halide lamps.
  • HPS lamps offer double the efficacy of mercury lamps, making them highly efficient for lighting large areas.

High-Intensity Discharge (HID) Lamps - Low Pressure Sodium Lamps

  • This lamp, also referred to as SOX. produces light of sodium's characteristic monochromatic deep yellow color, making it inapplicable for general lighting.
  • Because of its very high efficacy of over 150 lumens per watt including ballast loss, it can be applied wherever color is not an important criteria.
  • SOX is widely used for street, road, and area lighting, as well as for emergency or after-hours indoor lighting.
  • Another desirable aspect of SOX lamps is their 100% lumen maintenance. This, coupled with the discharge lamp's typically long life (18,000 HRS), make SOX lamps the most economical source available today in terms of cost per million lumens produced.