Lighting  »  Lamps

LEDs were first introduced as indicator lights in the 1960s. At this time, they were only available in red and had a very low efficiency of 0.01 lm/W. As the efficiency was raised quickly, today's commercial LEDs are comparable to CFL-Lamps. The typical efficacy of the LED lamps in the year 2010 was between 40 and 60 lm/W with the best LED lamps achieving luminous efficacy in the range of 90-100 lm/W. High-Power LEDs can already deliver more than 100 lm/W and in laboratory test values up to 200 lm/W have been measured. But until now, these values have not been transferred into practical applications. While much attention is placed on LED improvement in terms of lm/W it should be mentioned that the efficiency of the whole system should be considered which consists of the LED-chips, the optic system, the electrical system and the heat sink system. But the manufacturers usually only publish values for the brightness or efficacy of the LED chip which doesn't include driver losses.

Light emitting diodes are semi-conductors and combinations of typically two or three inorganic elements, such as gallium phosphide or gallium indium nitride. When an electric field is applied to the material, negatively charged electrons and positively charged holes are produced. When these recombine, the release energy is converted into a photon of light with a frequency that is equivalent to the band gap energy. As the emission of light is in a very narrow spectrum (monochromatic) intermediate processing is needed to get white light from LEDs.

LEDs are fast replacing CFLs and Linear Fluorescent lamps. In order to make use the existing luminaire and lamp holder designs, LEDs in the shape and of the base (such as pin and screw) of that of CFLs and linear fluorescent lamps (to be used with the existing ballast system for T12 or T8) are available in the market. 

LEDs can have an extremely high lifetime. While incandescent lamps have an average lifetime of about 1,000 hours and fluorescent lamp typically between 10,000 and 20,000 hours, LEDs can have life-times of 50,000 hours and more. This means, that a LED light that is used 11 hours/day for 250 working days/year will last for about 18 years. This being said, the lifetime of LEDs depend on their working temperature. In an environment with high temperature LED do not do well. Light emitting goes down and lifetime will be shortened. LED efficacy is higher with lower temperatures and this is the reason why good heat transmission from the LED lamps is very important.

The light emission of LEDs degrades. The degradation is the reason, why an end of life-time for LEDs has to be defined. Typically this end of life is defined as when the illuminance of a lamp is reduced to 70 percent of its original illuminance. The long lifetime of LEDs in practice means that reduced maintenance work is necessary for changing bulbs.

Operating temperature
LED lamps are more temperature sensitive than incandescent bulbs. It is important to choose a lamp which will work well at the temperatures to which it is likely to be exposed. For outdoor luminaires in climatic zones with cold winters, it is for example, advisable to select a lamp that also works when it is freezing.

Luminaires and applications
As consequence of the quick development during the last decades LEDs are appropriate for a wide range of applications. LEDs have been fast replacements for general and spot lighting in place of CFLs and linear fluorescent lamps for general purposes. Luminaires are being designed to accommodate LED bulbs and tubes into holders designed for CFLs and tubes. In addition LEDs are also taking over specialized applications in indoor areas such as architectural, accent lighting and outdoor areas such as parking lighting, street lighting and flood lighting etc.

A fluorescent lamp tube is filled with a gas containing low pressure mercury vapor as well as argon, xenon, neon, or krypton. The inner surface of the bulb or tube is coated with a fluorescent (and often slightly phosphorescent) coating made of varying blends of metallic and rare-earth phosphor salts. The mercury atoms in the fluorescent tube must be ionized before the arc can "strike" within the tube. As a result of this high initial power requirement fluorescent lamps need a special device known as ballast, which helps to regulate the electric current through the device. Ballasts are an important part to many modern high-efficiency lamps and they can be found as either conventional ballast or electronic ballast. For CFLs ballasts are usually integrated into the lamp.

There are many different CFL types with very different characteristics and qualities in the market. To find the suitable product can be a quite challenging task for a consumer. While selecting a CFL attention has to be paid to the type of fitting (socket), light output and other features such as dimmability, quick start, light colour etc. The large variety of CFL products available on the market means that smaller businesses may find it difficult or even impossible to have all the different CFL varieties in stock. An overview of the most energy-efficient CFLs in each class is given on the website www.topten.eu. The website is listing the most efficient LED and fluorescent lamps. For example compact fluorescent lamps with an e27 socket, tubes and medium lamp size.

A fluorescent lamp tube is filled with a gas containing low pressure mercury vapour as well as argon, xenon, neon, or krypton. The inner surface of the bulb or tube is coated with a fluorescent (and often slightly phosphorescent) coating made of varying blends of metallic and rare-earth phosphor salts. The mercury atoms in the fluorescent tube must be ionized before the arc can "strike" within the tube. As a result of this high initial power requirement fluorescent lamps need a special device known as ballast, which helps to regulate the electric current through the device. Ballasts are an important part to many modern high-efficiency lamps and they can be found as either conventional ballast or electronic ballast. Linear fluorescent lamp consists of a straight tubular of various diameters form and bi-pin electrical connections at either end. Popular lamps in home and office applications are T12 (38 mm diameter), T8 (26 mm) and T5 (16 mm).

T12 (38 mm diameter) was in principle the first linear fluorescent lamp that dominated the market for a long time. However, because of its quite low efficacy (compared to advanced technologies) it is no longer used in new installations. The lamp has a diameter of 38 mm (see figure below). From 1970 onwards, T8 (26 mm) increasingly substituted T12 lamps. The T8 typically has an efficacy 10 to 20% higher than T12. In countries where the operating voltage is 220 to 240 V, T12 lamps can directly be substituted through T8. As a result the market-share of T8 lamps grew quickly in these countries, while in countries witch are operating at 120V, the T8 lamps require new luminaries which slowed the penetration of T8 lamps in these areas. In 1995, the slim T5 lamp (16 mm) entered the market. The T5 lamp has a higher efficacy than T8 (about 5 to 10 %) and reaches an output of up to 105 lumen/Watt. It is always combined with electronic ballast.

T8 and T5 lamps are now the most common standard linear fluorescent lamps, e.g., in Europe. On the other hand, a higher fraction of T12 lamps can still be found in the USA and many countries in transition and in developing countries. The highest concentration of T12 lamps can be found in the countries formerly belonging to the Soviet Union. In 2005, the share of T12 lamps in the light output in the commercial building sector in these countries was about 95%. Under good circumstances T5 lamps can be up to 35% more efficient than their T8 counterparts (IEA 2006, p. 119). Compared to T8 lamps additional advantages of the T5 lamp include:

• T5 lamp in practice has an additional 10% efficacy due to its operating temperature
• Better luminaire output due to narrowness and minimal self shading
• Reduced lumen depreciation of only 5% after 12,000 hours

Lamp coating also affects the performance of Flourscent lamps like T5, T8 etc. Typically there are three different types of coatings. They are Halophosphate phosphors coating, achieving a CRI from 50 to 75; Three-band phosphor coating (triphosphor coating), achieving a CRI from 80 to 85; Multiband phosphor coating, achieving a CRI of 90 and above, albeit reduced efficancy comapared to triphosophor lamps. During the life of a fluorescent lamp, the phosphors age and the lamps light output decreases. However, multiband and triphosphor coatings age more slowly than halophosphates. Therefore, these lamps have improved lumen maintenance. Triphosphor lamps not only consume around 8% less energy than halophosphate lamps but also produce approximately 10% more lumens/Watt at a higher Colour Rendering Index. As a result thriphosphor lamps are the preferred technology choice.

Low-pressure sodium vapour lamps are discharge lamps in which light is produced by radiation from sodium vapour. It is the lamp with the highest luminous efficacy rating (up to 200 lm/W). A key weakness of this class of lights is a very poor colour rendering index, almost nearing 0. Low-pressure sodium lamps have an extremely narrow emission spectrum resulting from the sodium vapour. Since this light spectrum is very close to peak photonic light sensitivity for human vision, the efficacy level is very high. Low-pressure sodium lamps have a colour rendering index of 0. That means that they do not render colour. For this reason, these lamps are used when colour is unimportant. They are mostly used in street lighting, parking lots and security lighting.

HID lamps generate light by creating an electric arc across tungsten electrodes. The electrodes are housed inside a transparent tube made out of fused alumina or quartz and filled with different gases and metals. These define the type of HID. The three main families of HID lamps are:

• Mercury vapour
• High pressure sodium
• Metal halide
• Xenon short-arc lamp (less common)

In these lamps, a material, such as sodium, mercury, or metal halide, is added to the arc tube. The lamp has three electrodes, one acting as a cathode, another as an anode and the remaining electrode used for starting. The arc tube contains small amounts of pure argon gas, halide salts and sodium vapour to aid in starting. Free electrons are accelerated by the starting voltage. In this state of acceleration, the electrons strike atoms and displace other electrons from their normal atomic positions. Once the discharge begins, the enclosed arc generates the light source.

Mercury vapour lamps are widely used around the world. High-pressure versions have efficacy levels of 23-60 lm/W (IEA, 2006: 126). Their lifespan is between 6,000 and 28,000 hours and their colour rendering index is 15-62. The higher colour rendering values can be reached by using phosphor coatings, but this is associated with a lower efficacy.

High-pressure sodium lamps have the highest efficacy of all HID lamps: 70-140 lm/W. Compared to low-pressure sodium lamps they have a lower efficacy but a higher colour rendering index (CRI between 21 and 83). They are more commonly used than low-pressure sodium lights. Beside applications for street lighting high-pressure sodium lamps are suitable for some indoor applications. Their lifespan is comparable to the mercury vapour lamps which lies between 5,000 and 28,000 hours.

Metal halide lamps are not as efficient as high-pressure sodium lamps but they produce a whiter, more natural light (IEA, 2006: 127). The initial efficacy is between 47 and 105 lm/W; their lifespan is between 6,000 and 20,000 hours and their CRI is 65 to 92. As with mercury vapour lamps, these lamps show significant lumen depreciation. For instance efficacies at 40% of lamp life are much lower than initial ratings.

Advantages and disadvantages of HID lamps
HID lamps offer important advantages over incandescent lamps and also some advantages over fluorescent lamps. High-intensity discharge lamps are still some one of the best performing and most efficient lamps for lighting large areas or across great distances. Besides good initial efficacy levels the HIDs show good optical characteristics. The small size of the metal halide arc-tube allows for excellent optical control. On the other hand extreme brightness of the lamp requires careful shielding and design. (IEA, 2006: 125 f). HID-lamps have long start-up and warm-up times and typically require several minutes to reach their full light level. Their light is not very comfortable because the lamps flicker. They are characterised by poor dimmability. In case of dimming, the light-output falls much faster than the power input and additionally the CRI tend to drop. Finally, the lamps must cool off before relit.

Tungsten halogen
Tungsten halogen lamps are a derivate of incandescent lamps. In contrast to incandescent lamps the bulb encasing the filament is filled with high-pressure halogen gas, which enables higher filament and bulb wall temperature. The higher temperature increases the lamps efficacy and also generates a whiter light. Tungsten halogen lamps have efficacies of 18-35 lm/W, a very high Colour Rendering Index of above 95 and a lamp life of 2,000 to 6,000 hours. The most efficient tungsten halogen lamps use a multi-layer dichroic metallic coating on the inside of the capsule. This raises the temperature of the filament and the efficacy of the system. Infrared dichroic tungsten halogen lamps have an efficacy of 28-35 lm/W. All halogen lamps are fully dimmable, but their efficacy declines steeply as they are dimmed (IEA, 2006).

Many tungsten halogen lamps operate at 12 volts and require a transformer. Tungsten halogen lamps using a transformer have longer lamp life but operate at lower system efficacy because of the energy losses in the transformer. These may even exist when the lamp is not in use but the switch is on the low-voltage side of the transformer. Halogen lamps are about 20 to 50% more efficient than incandescent lamps but still show a relatively low efficacy. That is the reason why, e.g., in the EU the less efficient halogen lamps are also included in the phase-out scheme of the EU.

Tungsten incandescent
The incandescent lamp is the oldest type of electric lamp still in general use. The most common lamps consist of a bulb containing a wire filament that is heated and emits light. Its practical form was invented in 1879 and while this basic design has undergone numerous changes in materials and manufacturing, the efficacy of such lamps is still low and their average lifetime is quite short (about 1000 hours). For this reason, many countries around the world have begun phasing out incandescent lamps for more energy-efficient alternatives. Of course the most common (inefficient) lamps also have some advantages:

• Incandescent lamps create a comfortable lighting colour
• Cheap (low upfront purchase cost)
• Available for many applications and varieties for different input powers
• Dimmable

The poor efficiency of the lamps and the increasing efforts to fight climate change in many countries has led them to the decision to phase out incandescent lamps.

Compact Fluorescent Lamps (CFLs) and Light Emitting Diodes LEDs can replace all types of incandescent lamps. Compact fluorescent lamps are very energy-efficient and at the moment the cost-effective form of general lighting. Fluorescent lamps save about three quarters to four fifths of the energy used by incandescent lamps but provide the same light level. However, mercury content in CFLs is a matter of quality concern. LED lamps are more efficient (and cost-effective) compared to CFLs and therefore a better alternate to both incandescent bulbs and CFLs.

The electricity saving of a CFL compared to an incandescent lamp is about 80%. Lifetime of CFL is about 10 fold longer. Although more expensive to buy, they are much cheaper to run and can have a lifetime up to twenty thousand working hours. With careful design they can replace incandescent and halogen lights in most general lighting situations. There are few quality related issues for CFLs compared to incandescent bulbs, such as light colour, warm-up times, lifetime, number of switches before failure, and mercury content. It is essential for market success that all CFLs on offer have at least a minimum level of quality regarding these issues. However, most of these issues are resolved by the use of LEDs. The best LED on the EU Market show an efficacy of about 90 lumen/Watt, which is more than the best CFLs. It is expected, that the efficacy of LEDs is further rising, while there will be only small progress with the further development of CFL.

LED lamps have some advantages compared to CFL, which makes them the preferred solution particularly for spotlighting:

• Small and directed light source
• Longer lifetime
• Deliverable in all light colours
• Dimmable (optional)
• Not sensitive to vibrations

Example for the energy and cost savings of the substitution of an incandescent lamp through a CFL and LEDs is shown in the table below:

Replacing larger halogen spots (150 to > 1,000 Watts) through spots based on metal halide lamp technology results in energy savings of around 50-70%.

Metal-halide lamps are member of the high-intensity discharge (HID) family of lamps; produce high light output for their size. Originally created in the late 1960s for industrial use, metal-halide lamps are now available in numerous sizes and configurations for commercial applications like in supermarkets and retail shops as in sports facilities and outdoor lighting.

Metal halide lamps generate 65-115 lumens per watt compared to tungsten halogen lamps which have an efficacy of 18-35 lm/W. The savings by replacing halogen with metal halides are about 50-70%, depending on the compared cases. The cost-effectiveness however, highly depends on the specific situation. Usually HID lamps will pay back because of their higher lifetime and lower maintenance cost and their higher efficacy. In table below a possible cost-benefit situation is given as an example.

For smaller spotlights with up to 100 Watts, LED technology is the preferred choice. They save 85% of energy compared to halogen spotlights and pay back within a few years. Halogen spot lights are frequently used in all type of shops and other commercial buildings. Small halogen spotlights (up to 100 Watts) can be easily replaced by more efficient halogen lights (coated halogen lamps) or even better through LED lamps with cost-effective energy savings of up to 90 %.

LED-spots are perfectly applicable to substitute halogen spotlights. This is valid also for tungsten halogen lamps, which operate at 12 volts and require a transformer. However, their initial purchase price is usually quite high. In addition, LEDs have specific advantages for spotlighting and are expected to be the lighting technology of the future. As can seen below, the savings in both cases are about 85%. Furthermore, the maintenance costs are lower, because the LED last about 10 to 25 times longer than the halogen lamps.

The new promising technology entering the efficient lighting scene is LED (light-emitting diodes). This technology has some positive characteristics which make it interesting for many uses:

• High lifetime (up to 50,000 hours and more) and therefore low maintenance costs
• High efficiency and still potential for further improvement (see below)
• Good colour rendering index
• Non sensitive to vibrations
• Light is free from IR and UV-radiation and has low heat impact
• Neutral for insects
• Mercury free and easy to recycle and dispose

LED lamps are perceived to be expensive than halogen lamps. But they have a twenty-fold lifetime and a good rate of return. Halogen lamps can easily be replaced through LED lamps. The upfront cost of the LED lamp in the described example is about tenfold compared to a conventional halogen lamp. But on the other hand the savings are 28 Watt or 80 % compared to the halogen lamp and the lifetime of the LED lamp is about 20 times longer. The total cost of lighting for the LED lamp is less than half compared to the halogen lamp. In the table the lighting cost (investment and electricity costs) are given for 10,000, 20,000 and 40,000 hours. The rate of return of the investment is depending on the hours of use, but simple payback time may be as low as one year. The efficacy of LED lamps varies between 50 lumen/Watt and 93 lumen/Watt.

Compared to older Linear Fluorescent Lamps (LFL) system existing LFLs offer energy savings of 80 to 90%, if the lighting system is optimised. T8 lamps with triphosphor coating can save about 15% of electricity compared to T8 with halophosphate coating and 20 to 25% compared to T12 while providing better light quality. Additional savings can be achieved with T5 lamps in dedicated luminaires and efficient ballast technology. Furthermore, T5s also have some important additional advantages.

Light in the commercial and public sector is mostly produced by linear fluorescent lamps. Modern lamps of this type are quite efficient as a result of technological development. However, it should be stressed that lamp efficiency is only one part of the whole system. To get good and efficient lighting the whole system has to be optimized.

T12 (38 mm diameter) was in principle the first linear fluorescent lamp that dominated the market for a long time. Because its efficacy is lower compared to the advanced technologies T8 and T5 it is no longer used in new installations. The T8 typically has an efficacy 10 to 20% higher than T12. In countries where the operating voltage is 220 to 240 V T12 T12 lamps can directly be substituted through T8. A higher fraction of T12 lamps can still be found in the USA and in many countries in transition and in developing countries. In 1995, the slim T5 lamp (16 mm) entered the market. The T5 lamp has a higher efficacy than T8 (about 5 to 10 percent) and reaches an output of up to 105 lumen/Watt. It is always combined with an electronic ballast.

If there are T12 lamps (38 mm diameter) in use then the efficiency potential can be improved by about 15 to 20% by changing these lamps for T8 lamps. If this change is combined with a change of the whole luminaire energy savings would be about 40 to 50%. With today’s best technology (a triphosfor lamp combined with a good luminaire) the savings would amount to 55 to 70%. Furthermore, if there is daylight available additional savings can be reached through daylight controlled lighting. A last step can be made through presence detectors which limit artificial lighting to when it is needed. In case of absence of persons in the room, the lights would be shut off.

With the advent of LED lighting technologies, replacement for LF lamps are available in the form of linear LED lamps, which fit into the existing luminaires for LF lamps. LEDs are much more efficient than T5s, albeit expensive, they save much more energy and money in the long run with their higher efficacy and longer lifetimes.

Where annual lamp operating hours are too low to enable economic use of LED spotlights, more efficient halogen lamps may be an alternative.

Tungsten halogen lamps have a very high Colour Rendering Index of above 95 but their efficacies is rather low and is only about 20% higher than the efficacy of incandescent lamps. The lamp life is in the range of 2,000 to 6,000 hours.

The standard halogen lamps can exchanged through tungsten halogen lamps which use a multi-layer dichroic metallic coating on the inside of the capsule. This raises the temperature of the filament and the efficacy of the system. Infrared dichroic tungsten lamps have an efficacy of 28-35 lm/W. These lamps will need about 30% less electricity compared to the standard halogen lamp. All halogen lamps are fully dimmable, but their efficacy declines steeply as they are dimmed (IEA, 2006: 113). Many tungsten halogen lamps operate at 12 volts and require a transformer. Tungsten lamps using a transformer have longer lamp live but operate at lower system efficacy because of the energy losses in the transformer.

Electronic ballasts save around 25 % compared to conventional electromagnetic ballasts and around 15 % compared to improved electromagnetic ballasts. Electronic ballasts have additional advantages and are usually cost-effective. Pay-back time is dependent on hours of use of the lighting system and the price for electricity.

All discharge lamps like fluorescent lamps, low-pressure sodium and High intensity discharge lamps require ballasts to function. The ballasts have the task to provide a high voltage to initiate the discharge of arc and then to stabilize the discharge arc in the lamp during normal operation. There are two broad categories of ballasts:

• Electromagnetic ballasts (also known as core and coil ballasts)
• Electronic ballasts (also called high-frequency of solid-state ballasts) (IEA, 2006: 138)

All ballasts require energy to function and furthermore influence the efficacy of the lamp itself. This consideration must be taken into account, when total electricity consumption and total efficacy of a lamp and ballast are assessed. In both ballast categories different quality and efficiencies can be found. Within the EU and other countries like China, Canada and USA the quality of ballasts (minimal efficiency) is regulated (IEA, 2006: 311).

The appropriate combination of a lamp and ballast must be considered as primary step when selecting a lighting system. "Accordingly, ballasts are tested by comparing the performance characteristics of the ballast under tests combined with a reference test lamp to those of an equivalent reference ballast combined with a reference lamp. Testing in this way allows differences in power, lumen output and colour rendering to be compared" (IEA, 2006: 138). By comparing different lighting options, these advantages have to be integrated into the cost-benefit calculation. If this would be done correctly, the decision always will fall to electronic ballasts (see tables below).

Comparison of different ballasts

The table compares the energy savings and efficacy of different ballasts. While a relatively inefficient conventional ballast running two 36 Watt linear fluorescent tubes consumes about 20 Watts, a low loss electromagnetic ballast reduces these losses to 11 Watts, whereas a typical electronic ballast consumes only about 4 Watt per 36 Watt lamp. In this example shifting from electromagnetic ballast to an electronic ballast reduces power consumption from 92 Watts to 80 Watts - but it also increases light output by 10 -15 %. In total the efficient electronic ballast results in a lighting efficacy improvement of 30% over the inefficient electromagnetic ballast.

The reason for this is not only lower energy losses of electronic ballast; additional savings result from the following:

• Light output is increased through electronic ballasts. This means that lamps with a lower wattage can be installed to produce the same amount of light. An even more cost-effective opportunity arises from installing fewer luminaires to get the same amount of light. The higher cost of the electronic ballast can partly be compensated through lower costs for the luminaires.
• The lamp life is longer. Combined with an electronic ballast the lifetime of a lamp can be prolonged by about up to 300 %. The prolongation of the lifetime is depending on the ballast which was used before and the average duration of the switch-cycle. The substitution of conventional ballasts through electronic ballasts reduces maintenance costs (replacement of ballast and labour costs) of the lighting system.
• The life time of high quality electronic ballasts is comparable with the lifetime of a high quality electromagnetic ballasts.[1]
• Electronic ballasts are available with dimming systems. This allows additional savings by dimming lamps when full light output is not required.

Electronic ballasts are cost-effective over their lifetime, though they are more expensive to purchase than electromagnetic ballasts.

Dimmable electronic ballasts will reduce electricity consumption even when no daylight harvesting is possible. Investment into this technology is economically viable when there several luminaires and ballasts on the same branch circuit.

With dimmable electronic ballast the light output of a lighting system can be adjusted according to the amount of natural light coming through the windows. The artificial lighting is then activated or slowly and steadily intensified when the daylight alone is not sufficient or reduced, when the light from outside gets brighter. As a result, the lighting systems delivers a constant lighting level by adding regulated artificial lighting to available daylight. Dimmable lighting systems have the additional advantage that decreases in light output from the luminaire over time can be compensated by the system. Without the dimming system, additional electricity consumption would be caused by the maintenance factor which has to be considered for the initial illumination level.

The additional costs for the dimmable electronic ballast and the control system can be offset by the additional savings of the system at least in bigger rooms. Even in rooms where no daylight can be used, the benefits from adopting the lighting level to the necessary illuminance level might be bigger than the additional costs. The table below shows the pay-back time for the additional cost of dimmable ballasts in a classroom. In rooms without windows the simple pay-back time of the additional investment will be 15 years. In rooms, where the dimmable ballast can harvest daylight, the pay-back time will be 6 years.

Cost-benefit of an investment into dimmable electronic ballasts in a seminar room compared to investment with electronic bal-lasts

The pay-back time of the investment into dimmable electronic ballasts is dependent on different factors, whereas the most important are the power of the system as well as the hours of use of the lighting system over the year.