The correct intensity of light must be provided for the task being illuminated, without producing glare, when striving for operating cost reductions.
The increasing cost of electrical energy and the growing interest in conservation are resulting in many lighting retrofits. However, many of these retrofits are carried out without concern for the duality of the illuminated environment (loss of light uniformity, excess glare, etc.). Using products now available, there isn't any reason why an energy retrofit should not maintain, if not enhance, the visual quality of the space involved while conserving electric usage.
Reasons to retrofit
There are three major reasons for retrofitting a lighting system: high utility costs, excess illumination and/or inappropriate lighting.
High utility costs. Growing utility costs are a highly motivated reason to carry out a retrofit. Times have changed, and the cost of providing electricity to a facility has substantially increased. Over the past 10 years, there have been major increases in the price of fuel used to produce electric power.
Excess illumination. Excess illumination results from several factors. These include: a change in the actual task usage of the space (the use of computers with video screens greatly changes the lighting requirement for task lighting); initial over design; and a reassessment of needs.
Inappropriate lighting. Inappropriate lighting is similar to excess lighting; however it includes lighting in areas where not needed as well as a lack of same where a need exists. Examples include lights left on when a space is not occupied or when there is adequate ambient daylight to perform a task. We experience these types of energy waste almost every day.
Once one or more of the above reasons are recognized, an analysis of the existing system should be carried out. This analysis should include a study of the various components of the lighting system, since retrofitting these systems can involve many or few components. An evaluation of the total system is highly recommended so that an accurate assessment of both the cost factors and the illumination aspects can be made.
The following main components should receive your attention.
The first and most obvious replacement consideration focuses on the lamps presently in the fixture. The Energy Policy Act of 1992 (commonly referred to as EPACT) addresses this with the elimination of full-wattage halophosphor fluorescent lamps. This ruling includes the entire group of these generally used lamps(e.g., cool white, warm white, daylight, etc.) because these lamps produce lower efficacy (66 to 77 lumens per lamp watt without consideration of the ballast) than present technology offers. And, most halophosphor lamps have poor color rendering. A good replacement is the triphosphor (rare earth elements) fluorescent lamp, which offers improvements in efficacy (80 to 82 lumens per lamp watt) while providing good to very good color rendering.
Reduced-wattage lamps with comparable reduced lumen rating are still available, in both the halophosphor and tri-phosphor types. These lamps are energy conservation replacements for full-wattage lamps and offer a 15% reduction in wattage. However, there is also an almost equivalent reduction in lumen output. For example, if you replace a full-wattage (40W), 4-ft, cool white, halophosphor fluorescent lamp rated at 3050 lumens with a reduced-wattage halophosphor lamp, the difference would be a reduction of wattage down to 34W and a reduction in light output down to 2650 lumens (a 15% reduction in wattage and a 13% reduction in lumens). There would be no difference in the color rendering between similar type lamps.
An example of a very simple retrofit would be to replace a full-wattage halophosphor lamp (probably cool white, the most commonly used) rated at 3050 lumens with a reduced-wattage triphosphor lamp rated at 2800 lumens. The result would be a savings of 6W per lamp (15% savings), with a reduction of only 8% of light output. This type of retrofit is possible due to the higher efficacy rating of the reduced-wattage triphosphor lamp.
Triphosphor lamps can readily be obtained from most lighting equipment sources; they are a standard product of all the major lamp manufacturers, each of which have their trade names for the lamp. Because each lamp manufacturer uses different trade names, the industry has standardized the identification of triphosphor lamps with the nomenclature "RE" for rare earth, compared to "CW" for cool white, "WW" for warm white, etc. In the lamp designation, the "RE" is followed by a "7" for a 70-to-79 color rendering index (CRI) (good rendering) or an "8" for an 80-to-89 CRI (excellent). After that, there are two digits that identify the correlated color temperature of the lamps in 100[degrees]K rating. Thus, the designation "35" indicates a 3500[degrees]K color temperature. An example of a full wattage, 4-ft, fluorescent ("F40"), triphosphor ("RE") lamp with a good color rendering index ("7") and color temperature equivalent to cool white at 4100K ("41") would be an F40/RE741 lamp.
The next option in retrofitting a fluorescent system is to change the ballast. This device provides a starting voltage that spikes to ignite the lamp; it also provides a constant arc current to maintain the lamp's operation. High frequency electronic ballasts, which have become a popular retrofit item during the past few years, offer substantial improvements in performance and reliability while also offering a major reduction in operating costs. A high frequency electronic ballast operates a lamp at 20,000 to 50,000 Hz, compared to 60 Hz for a magnetic type. This high frequency causes the lamp to operate about 10% more efficiently, with a decreased ballast input wattage for the same lumen output.
Harmonic contribution. In 1994, the lighting industry finally produced a document that set performance standards for high frequency electronic ballast operation and safety: ANSI C82.11-1993, High Frequency Fluorescent Lamp Ballasts. This new standard establishes, as a maximum value, a 32% total harmonic distortion (THD). In most cases, the THD for electronic ballasts today is the range of 20%, and some ballasts even offer lower values. For the most part, you get what you pay for. There are ballasts made today that produce very low harmonics (in the range of 5%). This low harmonic level has no effect on the power consumed but may have a very dramatic effect on the extent of harmonics present. These ballasts also cost more. For comparison, the magnetic-type ballast (core and coil type), which has been the standard used with most fluorescent lamps, has a THD of approximately 24%.
Unlike fundamental currents that cancel each other at the neutral of a 3-phase wye circuit (partially or completely, depending on the load balance), the THD currents from each phase are additive. If a circuit using a magnetic ballast system with 24% THD is totally balanced, the total current flowing through the neutral will be approximately three times 24% of the 80% permissible loading (for each phase) per the NEC, or 58% of the maximum current allowed on any one of the three balanced phases. It can be less than that when any phase has a lower current than is allowed.
When high frequency electronic ballasts are used, the maximum current on the neutral, based on the allowed percentage of THD from ANSI C82.11-1993, will be three times 32% of the 80%, or 77% of the maximum current allowed on any one phase. In this scenario, as with the case above, the currents at the neutral will be well below the neutral's capacity and will conform to an acceptable installation.
Before ANSI C82.11-1993 was adapted, there were some cases of electronic ballasts exceeding the 32% now established as a limit. This could possibly cause a dangerous overload situation on the neutral conductor. When designing or retrofitting a lighting system, you should specify electronic ballasts that meet or exceed the requirements of the ANSI standard.
Ballast factor. A function of the combined lamp/ballast operation is ballast factor (BF), which is the percentage of lumens from a lamp that is operated by the actual ballast being used, compared to the lumens from the same type lamp operating with a test bench or laboratory standard ballast. This means that BF represents the percentage of lumen output of lamps based upon their lumen rating. Magnetic ballasts used today operate at about 94% BF (94% of labeled or rated lumens) for full wattage (40W) 4-ft, T12 lamps; for reduced-wattage (34W) lamps, magnetic ballasts will operate at 87% BF.
Due to the circuitry of high frequency electronic ballasts, such ballasts can be designed to have a low (around 70%), normal (around 85 to 95%), or high (above 100%) BF.
The lumen output of a lamp is the lumen rating of the lamp multiplied by the BF of the ballast used. Thus, depending upon what BF is chosen when specifying high frequency electronic ballasts for a lighting system, the lumen output of the lamps being served will have a corresponding percentage output based on the lamp's rated lumens. Lamp life does not appear to be substantially affected when using relatively low or high BF. However, when a lamp is operated at below 70% BF or above 130% BF, lamp life will decrease. Thus, selecting a ballast's BF can be an important element in obtaining the desired lighting level.
Power consumption. Power consumption by the lamp/ballast combination varies almost linearly with the ballast factor. For example, a two-lamp, 4-ft, T12 fluorescent system will require 52W at 77% BF and 60W at 88% BF. Fig. 1, details different ballast factors for various magnetic and electronic ballasts.
[Figure 1 ILLUSTRATION OMITTED]
When considering a retrofit using electronic ballasts, the next obvious consideration is to use T-8 fluorescent lamps ("8" means 8/8 or 1 in. in dia) in lieu of T-12 lamps ("12" means 12/8 or 1 1/ 2 in. in dia), the latter being the most commonly employed today. The 4-ft, T-8 lamp is rated 32W and 2850 lumens (all are at least RE7), which means a lamp-only efficacy (not including ballast effect) of 89 lumens per watt, compared to a 4-ft, T-12, RE7 lamp rated at 40W and 3200 lumens, with a lamp-only efficacy of 80 lumens per watt.
The contact pins for T-8 and T-12 lamps have the same size and configuration; thus, the lamps appear to be interchangeable. Physically, they can be interchanged but be careful: T-8 lamps will require a different ballast to operate properly.
The incandescent lamp, still one of the most popular types (but quite inefficient, as shown in Fig 2, and Fig 3) can also be retrofitted. The standard medium base lamp can be replaced with a compact fluorescent lamp (CFL) and ballast package with the CFL lamp wattage rating at approximately 33% of the incandescent wattage. However, you must be careful about lamp size and shape; you must make sure that the CFL is compatible with the space available within the fixture. The shape and position of the CFL lamp can also affect the quantity and distribution of light output of the fixture.
[Figure 2 and 3 ILLUSTRATION OMITTED]
Reflector-type lamps (R and PAR types) with a diameter exceeding 2 1/2 in. are also controlled by EPACT, with a requirement for higher efficacy as of October 1995. This will result in most of these types of lamps being replaced with halogen types, which produce approximately 20% more light for equivalent wattage. The standard 150W, PAR 38 lamp in use today can be replaced with a newly designed 90W, PAR 38 halogen lamp with almost no reduction in light output. A rule of thumb is that there is a saving of approximately 40% power using the new halogen PAR lamp, compared to a conventional PAR incandescent lamp. However, this is not true for the R lamp as, presently, there is no halogen lamp that can replace it.
But this is not the final answer. The technology of infrared reflection (JR) for halogen sources is a major breakthrough. This technology consists of a film on the outer wall surrounding the tungsten filament that reflects the infrared energy back onto the filament. The result is extremely high efficacy, over 25 lumens per watt, compared to 10 to 15 lumens per watt for standard incandescent and 15 plus lumens per watt for the halogen lamps. A 60W halogen IR-type PAR 38 lamp will produce almost the same illumination intensity as a standard 150W source, with a 60% reduction in consumed power.
The incandescent lamp will never become fully obsolete. A basic concept when using this type lamp is to stop selecting lamps by wattage. Instead, use the lumen rating of the lamp (the actual light output) at the operating voltage, and then compare the watts used by the various sources that produce the actual lumens desired. For example, a 60W incandescent can be replaced with a 52W halogen lamp or a 18W CFL/ballast module. And, the compact fluorescent has a rated lamp life of 10,000 furs, compared with 1000 hrs and 2500 hrs respectively for incandescent and halogen lamps. Another example is a 60W, 120V standard lamp that will produce 900 lumens. A 130V-rated lamp will have to be 75W to produce the equivalent lumens at 120V. Although the 130V lamp will have a rated life of approximately 3000 hrs when operating at 120V (thus being considered along life lamp) compared with 1000 hrs for 120V use, the long life lamp will consume 75kWh of energy per 1000 hrs of operation, versus 60kWh of energy for the regular lamp. The extra 15kWh cost results in an additional $1.50, at $.10 per kwh. Additionally, the long life (130V rated) lamp costs between two to four times as much as the standard lamp. Therefore, the additional cost of energy, without any savings in lamp cost, make the standard lamp the most cost-effective choice, unless the labor cost to replace the lamp is extremely high. Then, the 10,000-hr-rated CFL package becomes the best selection.
A further result of the EPACT legislation is that all packages for medium-based screw-in lamps will have to have rated lumens, wattage, and lamp life at the operating voltage clearly marked on the package.
High intensity discharge lamps
For energy savings, there are some direct replacement lamps within the family of high intensity discharge (HID) lamps, though the replacement lamps are very specialized. The HID types include mercury vapor (MV), metal halide (M-H), and high pressure sodium (HPS). To obtain better color as well as operating cost improvements, MV lamps should be replaced with M-H lamps whenever possible. The following ratings of MV lamps can be replaced: 175W, 250W, 400W, and 1000W. For the 400W and 1000W lamps, the M-H replacements are the 325W and the 950W units respectively. In addition to a reduction of power usage, these lamps will provide improved color rendering (65 to 70 CRI for the M-H compared with 45 CRI for the MV). The lumen output of the M-H replacement lamp will increase by 30% for the 325W (a 75W savings) and over 50% for the 950W (a 50W savings). The 175W and the 250W M-H replacement lamps will provide greater luminance and better color rendering but no reduction in power.
The HPS replacement lamps cover all of the conventional sizes, with the 150W HPS replacing the 175W MV, the 215W HPS for the 250W MV, the 360W HPS for the 400W MV, and the 880W HPS for the 1000W MV. Power savings range from 10% to 16%, with an increase of as much as 50% in lumen output. The coloring rating of the HPS lamps is 22 CRI, which, like the MV they replace, is poor.
There are some concerns regarding HID lamp replacement. These include ballast compatibility, which should be verified with each installation, and lamp shape, which can greatly affect the photometric performance. In many instances, the easiest way to confirm satisfactory replacement operation is to actually try one or two replacement lamps.
Most ballasts that are presently used for HID lamps are still the core-and-coil (magnetic) kind specially designed for each particular type HID lamp. The exceptions are some electronic ballasts that have been developed for 50W and 70W M-H lamps; these ballasts operate the lamp more efficiently and are considerably smaller and lighter.
With the expanding use of HID lamps, it appears that the next step will be the development of electronic ballasts designed to accommodate most of the HID lamps now available. It's not known when these ballasts will be available or what special features, if any, they will have. In regard to M-H lamps, which can take more than 10 min to achieve full light output during restart (when hot), a potential benefit of using electronic ballasts is that the circuitry design of the ballast may allow a more rapid restart.
In addition to lamps and ballasts, light fixtures have two key components that play an important role in providing illumination: the internal reflector and the shielding (lens or louver) medium. These two components control where the light is directed and how efficiently the light is transmitted. Because of their key roles, most retrofit schemes can involve one or both components.
One of the most over-emphasized retrofit procedures for fluorescent fixtures is the installation of a specular reflector inside the fixture. The original white painted reflector that most fixtures use has about an 89% (scattered) reflection. This means it reflects 89% of the lumens that strike the surface, but not in a mirror-like manner. The reflected component of the generated light is somewhat diffused. As a light fixture ages, the internal reflector becomes dirty and does not reflect the original rated value. But, if the fixture is cleaned when the lamps are replaced, the reflector again will approach its original rating, to about 85%, unless the paint finish has been severely degraded. The most effective specular reflector has a 95% efficiency; an average specular reflector has about a 93% efficiency, about 8% to 10% more reflectivity than the cleaned painted surface.
Because a specular reflector can be shaped to redirect the light, it can affect the direction of light from the fixture and produce more or less light at different locations in a room. There are two distinct ways in which shaped specular reflectors can be effective. In the first situation, a combination of retrofitting the fixture with a specular reflector and replacing full wattage halophosphor lamps is carried out; however, the original ballast(s) remains. The replacement lamps are energy saving (T12) RE7 lamps, the total fixture is cleaned, and a new specular reflector installed. The resulting light level will be between 95% to over 115% of the level at the time prior retrofitting, depending upon the operating time of the existing lamps and dirt accumulation prior to retrofitting. The resultant light output of the retrofit will be accompanied by a 15% savings of power and energy usage. While there is an energy savings, it's doubtful whether there is a reasonable payback.
The second situation would be a retrofit with specular reflectors that would also include replacement of the lamps and ballasts. The result can be a major improvement of the power consumed. Consider a typical 2-by 4-ft fluorescent fixture with three, 4-ft, T12 reduced-wattage halo-phosphor lamps, using tandem wired magnetic ballasts for each pair of fixtures (three 2-lamp ballasts for each set of two fixtures). The power being consumed is 123W per fixture. If this fixture was retrofitted with a specular reflector insert and electronic ballasts, and if the lamps, sockets, and ballasts were reconfigured to two 4-ft, T-8, RE 7 lamps, the illumination output of the retrofitted fixture would be from 80% to 115% of its original value, with a 50% to 30% savings in power usage respectively, depending upon the ballast factor of the replacement ballasts.
Lenses and lowers
A fixture's lens is the plastic or glass material located at the fixture opening. It allows the light produced within the fixture to pass through it unaffected, or to be directed in a diffused mannerr, or to be redistributed from concentrated to wide distribution. By itself, a lens cannot actually save energy, but in combination with lamp and ballast changes, a lens can be used to redirect the light for a more usable distribution of illumination. There are also retrofit parabolic louvers that can be used. These have 1-in. to 2-in. square openings and are 0.75 in. to 1.2 in. deep.
Certain lenses can change a fixture's light output to a very wide distribution, with the greatest candlepower located between 20 to 50 degrees out from either side of an imaginary line directly below the fixture. In comparison, a standard lens generates its greatest light distribution between 0 to 25 degrees.
A lens retrofit allows the fixture to provide a wider and more uniform distribution. In turn, this may allow fixtures to be spaced further apart, which means fewer lamps and lower operating costs. Or, lamps and ballasts can be removed from existing fixtures while light uniformity is maintained.
On the other hand, the open-type parabolic louver has a distribution similar to a standard lens, but with the advantage of having more lumens transmitted through its openings. The brightness cut-off is approximately 45 degrees from either side of an imaginary line directly below the fixture. These louvers are applicable for use in visual display terminal (VDT) computer environments.
RELATED ARTICLE: TERMS TO KNOW
Color rendering index (of a light source): Also known as CRI. The degree of shift that color pigments of objects undergo when illuminated by a light source as compared with the color of the same object when illuminated by a reference light of source of comparable color temperature.
Efficacy: The ratio of the total luminous flux being emitted from a light source divided by the total power input going to the light source. It is expressed in lumens per watt.
Halophosphor fluorescent lamp: A commonly used fluorescent lamp that employs a calcium halophosphate coating applied to the inside of the lamp. This coating radiates energy across the entire visible spectrum.
Triphosphor fluorescent lamp: A fairly recently developed fluorescent lamp that uses three types of rare elements in the phosphor coating applied to the inside of the lamp. When activated, each of these elements visually peaks at different areas of the visible spectrum. These three wave lengths are better matched to eye sensitivity than the light output of the halophosphate coated lamps.
Total harmonic distortion: Also known as THD. Basically, this phenomenon relates to the sum of all the harmonic waves, being multiples of the fundamental (60 Hz wave), present in a circuit or in an electrical system. Specifically, it is the square root of the sum of the squares of the RMS (root mean square) harmonic voltages or currents divided by the RMS fundamental voltage of current.