LIGHT SOURCES IESNA ED-150 Module 5

Purposes of this session: To review the basics of the three major light source families To highlight the latest developments in each of these families To discuss the principles behind new light sources As part of an intermediate lighting course, this module assumes that the basic operating principles of the major light sources are already understood. These principles are briefly summarized in this presentation on those slides that include the word, “Review,” in the title. The focus of this module is not to teach the basics but to delve into newer developments in light sources.

LIGHT SOURCE FAMILIES Filament / Incandescent Lamps « Fluorescent Lamps High Intensity Discharge Lamps

Review of “Incandescence” Basic principle: heat a solid material until it glows Material used today: tungsten Spectral power distribution: Because the output energy is proportionally weighted toward the longer wavelengths (“red”), incandescent lamps are considered a “warm” light source.

Incandescent Lamp Shapes A few of the most common shape designations are: A = arbitrary; C = conical; F = flame; G = globe; E = elliptical; MR = mirrored reflector; ER = ellipsoidal reflector; PAR = parabolic aluminized reflector; T = tubular. (IESNA)

Voltage relationships for an incandescent lamp This graph shows how variations in input voltage affect various performance characteristics of incandescent lamps. A few of the most important relationships are summarized on the next slide. (IESNA)

Voltage relationships for an incandescent lamp Voltage & light output At 80% rated voltage, light output is 40% At 110% rated voltage, light output is 130% Voltage & life At 90% rated voltage, life is 400% At 110% rated voltage, life is 30% The voltage and light output relationship shows that as an incandescent lamp is dimmed, light output changes at a much faster rate than the voltage. The voltage and life relationship shows that even a small increase in operating voltage above that which the lamp is rated can significantly reduce lamp life. On the other hand, reducing the operating voltage below the lamp’s rated voltage can significantly increase lamp life – useful, for example, when using an incandescent lamp in a hard-to-reach application.

Review of the Tungsten-Halogen Cycle Figure a illustrates how tungsten molecules that evaporate from the filament in a standard incandescent lamp are carried to the bulb wall by convection currents, where they condense and deposit on the bulb wall. The tungsten-halogen cycle is shown in Figure b. In this cycle, the evaporated tungsten molecules combine with halogen molecules, and so do not condense at the bulb wall. Instead, the tungsten halide molecules are carried back near the filament, where the high temperatures cause them to dissociate, and the tungsten is redeposited onto the filament. (IESNA)

Benefits of Tungsten-Halogen Lamps Reduced bulb wall blackening Higher lumen maintenance Higher CCT Generally perceived as less “yellow” or “whiter” Higher lamp efficacies Longer lamp life

Filament Lamp Performance These graphs show the steady decline in light output and LPW over the life of a filament lamp. The upper graph is for a standard incandescent lamp type; note that light output declines by 15-20% by the time rated life is reached. The lower graph is for a tungsten-halogen lamp, and shows that light output only declines 5-8% by rated life for these types. (Note that the vertical and horizontal axes for the two graphs are not at the same scale.) (IESNA)

What’s new in incandescent lamps? IR coatings In standard tungsten-halogen lamps the IR energy (heat) all passes through the quartz capsule containing the filament In IR lamps, a dichroic coating on the quartz reflects the IR energy back to the filament The hotter filament produces more light without more power higher LPW!

LIGHT SOURCE FAMILIES Filament / Incandescent Lamps Fluorescent Lamps « High Intensity Discharge Lamps

Review of “Fluorescence” Basic principles: 1) energize low pressure mercury vapor - produces UV photons 2) phosphor coating absorbs UV photons 3) phosphor coating re-radiates the energy as visible light Spectral power distribution: varies, depending on the chemical composition of the phosphor coating

Review of “Fluorescence” This figure illustrates the fluorescent light production process, as described on the previous slide. (IESNA)

Fluorescent Lamp Review This shows the energy distribution for a typical T12 fluorescent lamp, operated at 60Hz. While only 21% efficient at converting its input energy to light, the fluorescent lamp is still three to four times more efficient than an incandescent lamp. (IESNA)

Fluorescent Lamp Shapes (IESNA)

Fluorescent Lamp Review: Life Life ratings for fluorescent lamps (as for all lamps) are defined as the time period at which 50% of a large sample of lamps continue to operate, while 50% have failed. For fluorescent lamps, the industry standard test method for determining lamp life is to operate the lamps for 3 hours, then turn them off for 20 minutes, then on again for 3 hours, then off for 20 minutes, etc. (IESNA)

Fluorescent Lamp Review: Life This graph shows how variations in the 3-hour operating cycle affect the life of a fluorescent lamp. As the lamps are operated for shorter time periods, the lamp life is reduced, due to the damage done to the lamp electrodes by the more frequent switching. At longer operating cycles, lamp life is extended. (IESNA)

Fluorescent Lamp Review: Life The failure mechanism for fluorescent lamps is the loss of emissive coating on the lamp electrodes (or cathodes). This figure illustrates the construction of the lamp near the cathode, and the coiled wire cathode with emissive coating. Each time the lamp is started, some of the emissive coating is used, so that more frequent switching leads to the reductions in lamp life shown on the previous slide. (IESNA)

Fluorescent Lamp Review: Ballasts 2 primary functions of all ballasts 1) provide sufficient voltage to start the lamp 2) control the current to the lamp while it is operating Additional functions of some ballasts 1) provide voltage to preheat the lamp electrodes before starting voltage is applied 2) maintain voltage to the lamp electrodes (for heating) while the lamp is operating All discharge light sources, including fluorescent and HID lamps, have negative resistance characteristics; that is, lamp current increases when lamp voltage decreases providing a runaway current condition unless ballasting is provided. The ballasting element that provides this current limiting can be a resistor, inductive reactor, or a high leakage reactance autotransformer. The ballast can also be electronic. For the additional functions, preheat and rapid start ballasts provide #1. Some rapid start ballasts provide #2. Instant start ballasts do not provide either of these additional functions.

Fluorescent Lamp Review: Ballasts Starting methods for fluorescent lamps Preheat Rapid Start Programmed Start Instant start Ballast Types Electromagnetic Electronic These are listed here simply as a reminder; the definitions and basic principles are assumed to be already understood. Proper starting and operation of fluorescent lamps by a ballast is very important for lamp life. In some cases, the emissive coating on a fluorescent lamp’s electrodes can be rapidly lost through a process known as sputtering. Sputtering can occur if a high voltage is applied to the electrodes before they are sufficiently heated, if the starting current is not high enough, if the current crest factor (CCF) is too high, or if a lamp is dimmed without maintaining sufficient electrode heat. The American National Standards Institute (ANSI) sets guidelines for many of these parameters for fluorescent lamp-ballast systems. One newer starting method, really a variation of rapid start, is commonly called programmed start. These ballasts do not apply the starting voltage to the lamp electrodes until after a measured pre-heating period, which should greatly reduce electrode sputtering. Program-start ballasts are common for T8 and T5 lamps.

Fluorescent Lamp Review: Electronic Ballast Operation This graph shows one of the primary benefits of electronic ballasts for fluorescent lamps: the lamp efficacy gains that are realized by operating the lamps at high frequencies. Other benefits of electronic ballasts include lighter weight, less noise, and cooler operation. The graph above is for T12 lamp diameters; smaller diameter lamps realize efficacy gains that are less than those shown. (IESNA)

What’s new in fluorescent lamps? T5 systems « CFL amalgam lamps Electrodeless lamps

T5 Fluorescent Lamp Systems Small diameter enables new luminaire designs Metric lengths and unique electrical requirements mean ballasts and luminaires must be designed for T5 lamp use Overall efficacy greater than T12 systems, higher source brightness than T8 lamps and better optical control Peak light output at higher temperature and better lumen maintenance than other lamps The opportunities for new luminaires are probably greatest in those cases where the luminaires are either visually prominent (i.e., indirect lighting, direct/indirect lighting, surface mount) or where the luminaires are concealed and space is limited (i.e., coves, valences, showcases). Note that these lamps have high luminances and should not be directly viewable. With the smaller, “tighter” luminaire designs possible for T5 lamps, the operating temperatures can be elevated. Unlike most other linear fluorescent lamps, which have their maximum light output at 25C ambient air temperature, T5 lamps are designed for maximum light output at 35C. T5 lamps are designed for operation on dedicated electronic ballasts. The small diameter means that the lamp electrodes, which can be quite hot, are very near to the bulb wall, increasing the risk of overheating and fire if the lamp electrode breaks and the ballast continues to send current to the lamp. As a result, most ballasts for T5 lamps include an end-of-life sensing circuit to ensure that the ballast shuts down once the lamp has failed.

T5 Fluorescent Lamp Systems: Lumen Maintenance This graph shows the improved lumen maintenance characteristics of T5 lamps, relative to other fluorescent lamps. (IESNA)

What’s new in fluorescent lamps? T5 systems CFL amalgam lamps « Electrodeless lamps

Review of CFL basics Compact fluorescent lamps (CFLs) have a variety of base and pin configurations. Two-pin lamps, such as the one shown above, use a glow switch starter in the base of the lamp and are operated by magnetic ballasts. Four-pin lamps do not have starters in the lamp base and are operated on electronic ballasts. All CFLs have dedicated bases and lampholders (sockets) to ensure system compatibility. Some configurations have “spiral” tubes to maintain a compact geometry while increasing the arc length. A CFL operates by the same principles as linear fluorescent lamps, except in the case of CFLs the arc passes through a series of bends in the lamp. This configuration causes the light output of a conventional CFL to change as a function of its operating position, as shown on the next slide. (IESNA)

These graphs show the light output to temperature relationship for a conventional non amalgam CFL, at different operating positions. The lamps lumen rating is based on “base up” operation at 25C – the peak light output conditions. When the lamp is operated in the base down position, as in a table lamp, its light output peaks at a much lower temperature, and at normal operating temperatures its light output is reduced by 10 to 20% from its rated light output. A smaller light loss is experienced in the horizontal operating position. (IESNA)

CFL Amalgam Lamps A mercury amalgam is added to the conventional CFL The amalgam serves to alter the light output to temperature relationship This change provides more stable light output from the CFL at different operating positions and when in “hot” fixtures One potential drawback is that the lamp’s warm-up time can be extended Another potential drawback is reduced dimming capability. An amalgam is an alloy of mercury and other metals. When placed in a fluorescent lamp, it determines the mercury vapor pressure in the discharge by absorbing or releasing mercury. It keeps mercury pressure in the discharge close to its optimal value as the lamp temperature changes. Amalgams are typically used with CFLs where the bulb wall is hot and a temperature control technique is necessary. The light output to temperature relationships are shown in the next slide.

This graph shows how the use of an amalgam in a CFL maintains the lamp’s light output over a much broader temperature range. While the actual performance details depend on the specific lamp in question, the overall effect of the use of amalgams in CFLs is that there is very little change in light output at different operating positions, or at the different temperatures typically encountered in CFL luminaires. (IESNA)

What’s new in fluorescent lamps? T5 systems CFL amalgam lamps Electrodeless lamps «

Electrodeless Fluorescent Lamps Remember that: 1) electrodes are used at each end of a conventional fluorescent lamp to initiate the electric arc discharge in the lamp 2) the life of a conventional fluorescent lamp depends on the loss of emissive coating from the lamp’s electrodes 3) conventional lamps operate at 60 Hz to 60 kHz, depending on the ballast Electromagnetic ballasts operate lamps at 60 Hz. Most electronic ballasts operate lamps within the range of 20 – 60 kHz.

Electrodeless Fluorescent Lamps At very high frequencies (2 - 15 MHz), an electromagnetic field can be directly induced in a low-pressure mercury lamp, without the need for lamp electrodes These induction lamps require more complex power supplies (ballasts) but can have extremely long lifetimes

Electrodeless Fluorescent Lamps This figure shows the principles by which an induction fluorescent lamp operates. 1) A radio frequency (RF) power supply sends current to an induction coil. 2) The current in the induction coil (simply a wire wrapped around a metal or plastic core) induces an electromagnetic (EM) field. 3) The EM field excites the mercury in the lamp, so that it emits UV energy. 4) The UV energy excites the phosphor coating on the inside of the glass, producing light. (IESNA)

LIGHT SOURCE FAMILIES Filament / Incandescent Lamps Fluorescent Lamps High Intensity Discharge Lamps «

HID Review: Mercury Vapor Energize high pressure mercury in small arc tube Result is line output (“spiky”) with short to medium wavelengths (blue to yellow) Very cool source with poor color rendering Limited applications today (IESNA) The reason mercury is seldom recommended for applications today is because of poor efficacy (lumens per watt) and poor lumen maintenance characteristics.

HID Review: Metal Halide Energize high pressure mercury with halide additives Additives serve to increase lamp efficacy and improve color properties Popular “white” light source for many exterior and interior applications (IESNA)

HID Review: High Pressure Sodium Energize sodium vapor at high pressure Sodium produces energy at wavelengths near peak human sensitivity, so high efficacy Spectral power distribution (SPD) is deficient in long and short (red and blue) wavelengths (IESNA)

HID Review: Warm-up and Restrike Time (IESNA)

HID Review: Lumen Maintenance (IESNA)

What’s new in HID lamps? Ceramic metal halide « Pulse-start metal halide Microwave lamps

Ceramic Metal Halide Conventional metal halide lamps use quartz for the arc tube Conventional metal halide lamps experience lamp-to-lamp color variability and color shift over life Use of a ceramic material for the arc tube allows higher operating temperatures and pressure

Ceramic Metal Halide Benefits of ceramic metal halide Higher initial light output (so higher LPW) Higher maintained lumens CRI >80 Improved color stability <200K shift in CCT over lamp life no lamp-to-lamp color variability Both magnetic and electronic ballasts are available for ceramic metal halide lamps, with system efficacy determined by the lamp/ballast combination.

What’s new in HID lamps? Ceramic metal halide Pulse-start metal halide « Microwave lamps

Pulse-start Metal Halide Conventional metal halide lamps (of >175 watts) have a starting probe in the arc tube and the ballasts do not use an ignitor Pulse-start metal halide systems have specially-designed lamps without a starting probe. An ignitor is supplied with the ballast to start the lamp with a high voltage pulse The newer lower wattage metal halide lamps (150 watts and less) were developed as pulse-start systems. Probe-start systems are only used in the higher wattage lamps.

Pulse-start Metal Halide Benefits of pulse-start metal halide Increased lamp efficacy and lumen maintenance Longer lamp life Faster warm-up and restrike times Lower cold-start temperatures More ballast options Lots of relative terms here with no specifics – only because the specifics depend on the particular product in question and the particular manufacturer. Note that pulse-start lamps typically require a ballast change if retrofitting.

What’s new in HID lamps? Ceramic metal halide Pulse-start metal halide Microwave lamps «

Microwave lamps Microwave energy (2.45 GHz) can directly excite a gas plasma discharge, without the need for lamp electrodes A small glass bulb contains the gas and must be rotated at high speeds for uniform light distribution Can provide very high light output from a small source The combination of high light output and a small source creates opportunities to use microwave lamps in remote source (light pipe) lighting systems.

Microwave lamps This figure shows the operating principles of a microwave lamp. 1) A magnetron generates a microwave field. The magnetron components are the same as those used for microwave ovens, and so are readily available. 2) The microwave energy travels through a waveguide into a cavity that holds the bulb. 3) In the cavity, the small spherical bulb (made of glass or quartz) rotates at high speed to stabilize the gas fill. 4) The gas fill, excited by the microwave energy, forms a plasma that emits light. (IESNA)

Purposes of this session: To review the basics of the three major light source families To highlight the latest developments in each of these families To discuss the principles behind new light sources «

New Lamp Technologies Electroluminescent « Light Emitting Diodes (LED) Not strictly speaking new technology, electroluminescent lamps are at least forty years old and in common use, especially in avionics. What is new is the recent development of a high intensity.

Electroluminescent Lamps Electroluminescence: process where a phosphor converts AC energy directly into light - no gas discharge required Phosphor layer is “sandwiched” between two two-dimensional (area) conductors AC field is established between the two conductors, energizing the phosphor

Electroluminescent Lamps An illustration of the phosphor layer between two area conductors. When the conductors are energized with an ac field, the phosphor is excited and radiates light. (IESNA)

Electroluminescent Lamps Color depends on the phosphor material and the frequency of the ac field Luminance depends on the phosphor material and the frequency and voltage of the AC field Low power, long life, low efficacy Dimmable without color change Useful life limited by lumen depreciation

Electroluminescent Lamps: Lumen Depreciation Electroluminescent lamps generally do not “burn out” in the traditional sense, so their useful life is often expressed as the number of hours after which the luminance falls to 50% of the original luminance. This rating varies greatly based on the phosphor, the frequency and the voltage. This figure shows the light output to operating hours relationship for two types of green electroluminescent lamps. (IESNA)

New Lamp Technologies Electroluminescent Light Emitting Diodes (LED) «

Light Emitting Diodes LEDs produce light by electroluminescence Low-voltage direct current is applied to a crystal that contains a p-n (positive-negative) junction Crystal is “doped” with chemicals Most common today are aluminum indium gallium phosphide (AlInGaP) and indium gallium nitride (InGaN) LEDs

Light Emitting Diodes This figure shows the p-n junction on an LED crystal. Light is produced at the junction when a low-voltage current is applied. (IESNA)

Light Emitting Diodes LED color is specified in terms of the dominant wavelength emitted. Common types are shown in this figure on the CIE chromaticity diagram. The location of the coordinates near the outer boundary of the diagram shows their relative “purity” or color saturation. (IESNA)

Light Emitting Diodes This figure shows some common LED configurations. the T-1 3/4 LEDs (a in the top figure) are available in amber, red and orange (AlInGaP) and in blue, green and blue-green (InGaN) and have been used for traffic signals, message signs, exit signs, and outdoor video displays. Higher intensity red and amber (AlInGaP) as shown in b at the top are used for automotive exterior lights. For illuminating large areas, a newer very high flux plastic packaging has been used with both AlInGaP and InGaN LEDs. For use on PC board assemblies, plastic package surface-mount (SMT) LEDs are used, as shown in the bottom figure. (IESNA)

Light Emitting Diodes: White LEDs Saturated colors of light are needed for some applications, but for many architectural uses white light is needed Can get “white LED” light by mixing red, green and blue LEDs More recent products use a blue LED (InGaN) with a photoluminescent phosphor phosphor emits broad SPD when energized by short wavelength energy from LED Development of LED sources is occurring rapidly, and many people believe they hold significant potential for architectural lighting applications. Their appeal is based on providing a very small, point source of light with very long life and low power. White light can be obtained in two ways; by mixing red, greed and blue, or by using a blue LED with a photoluminescent phosphor.

Light Emitting Diodes: White LEDs This graph shows the SPD for a white LED that combines a blue InGaN LED with a photoluminescent phosphor to provide a broad overall SPD. (IESNA)

SUMMARY To review the basics of the three major light source families To highlight the latest developments in each of these families To discuss the principles behind new light sources