TYPES OF LIGHT BULB BASES

Find the light bulb you need using this visual light bulb base chart and detailed illustrations of general light bulb bases, fluorescent bases and specialty halogen base types.

WHAT IS THE DIFFERENCE BETWEEN LIGHT BULB BASES?

There are tens of unique bases for light bulbs. The most familiar is the Edison screw base found on most incandescent bulbs and many halogen, compact fluorescent, HID and now LED bulbs.

The common terms are medium, intermediate, candelabra and mogul. However, because the light industry likes mysterious codes, you may also see E26, E12, E39, etc. E obviously is for Edison. The number after the E is the diameter of the base in millimeters (mm).

Here are the most common Edison base names, codes and applications:

The large Mogul bases found on higher wattage incandescent and HID bulbs are E39.

Most Edison base bulbs are called "single contact" because there is one contact button at the center of the base. 

This document is from four-bros.com blog, thanks so much!

Fulham Ballast Chart for 2D / 2-D / Butterfly CFL Bulbs.

Lighting 101: All About Bulbs

There is much discussion about different light fixture designs; however the most important aspect of fixtures is the actual light source. There are many bulb options out there and this week we will be discussing the advantages, disadvantages, and optimal usages of each bulb type. This discussion is especially important now with the high-profile promotion of various ‘eco-friendly’ bulb options.

Efficacy- light source efficiency- How much of the electricity put into a bulb is lost to heat instead of converted into photons (light). The more energy lost to heat the lower a bulbs efficacy.

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Incandescent Bulbs

Incandescent are the original light bulb that brought electrical light to the masses. Although it uses an inefficient method for producing light, there are some definite advantages to incandescent bulbs. The main draw to the incandescent bulb is it produces a pleasant warm light that is effective for both directional and ambient light. Another advantage is the bulb itself is quite elegant, which lends itself well to bare-bulb applications such as chandeliers.

Some of the drawbacks to incandescent bulbs are low efficacy and a short lifespan. Incandescents run hot while in operation. The heat from the bulb is directly linked to the efficacy of the bulb. When converting electricity into light, some of the energy is also converted to heat. In incandescent,

Retto 1 lt Wall Sconce

halogens, and HID’s a large percentage of the energy is translated into heat instead of light (thus lowering its efficacy).

Incandescent Fixtures

Retto- This fixture comes in wall sconce and flushmount models. Using bulbs with large ‘antique’ style filaments, the fixtures highlight the beauty of the bare incandescent bulb.

 

 

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Halogen Bulbs

Halogen bulbs represent an advanced version of the standard incandescent bulb. The gas within the bulb allows for higher operational temperatures which produce a hotter light more closely resembling sunlight. Additionally the bulbs have a longer lifespan due to the properties of the gas. Halogen bulbs tend to be smaller than incandescents, which allow them to be used in a variety of applications such as under cabinet lighting and task lamps.

Halogen bulbs due to their small size and higher operational temperatures tend to have hotter outer glass while operating. Properly rated fixtures that have safety certifications are recommended to ensure safe use of halogens.

Halogen Fixtures

Hazelton 31 lt Chandelier

A large percentage of Eurofase’s lighting fixtures utilize G4, G9, or B10 halogen bulbs. This is due to their dependability, longevity, small size, and clean bright light.
Hazelton- This fixture utilizes the small, unobtrusive nature of G4 halogen bulbs to light glass spheres filled with crystals. The light source is ideal because it is slightly warmer than white light without being yellowish, which augments the amber hues of the glass.
Nava- This fixture exhibits how seamlessly halogen bulbs have displaced traditional incandescent bulbs. Utilizing the candelabra B10 bulb, the blue glass fixture exhibits the adaptability of the bulb’s light. Although slightly warmer than pure white, the light isn’t too warm so still looks great against a cool color!

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HID Bulbs

Also known as arc lamps, these are generally used for high-output applications like outdoor, streetlights, and warehouse lighting. The bulbs require ballast and an igniter to start, and are generally quite expensive. After ignition the bulb generally requires several minutes to reach optimal light output. Additionally, when turning off a lamp, it generally requires several minutes of cooling before it can be relit, commonly known as ‘hot restrike time’ (This can be avoided in smaller bulbs such as our under cabinet Xenon lights). Some examples of HID lamps are metal halide, sodium vapor, xenon, and the older mercury vapor and carbon arc bulbs.

HID bulbs generally have 2-3x the lifespan of incandescents, and have a higher efficacy (although still not as good as fluorescent and LED sources). Besides some metal halide lights (and Xenon) the bulbs do not produce ideal ‘living light’ and as such are not commonly used for indoor applications.

G4 Xenon MiniPuck

HID Fixtures

Eurofase supplies a variety of Xenon MiniPuck lights and under cabinet fixtures.
For architectural recessed and outdoor lights that utilize HID bulbs feel free to peruse the offerings on our website.

 

 

 

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Fluorescent Bulbs

Fluorescents are popular due to their long life, energy efficiency, even glow, and the plethora of fixtures and formats currently available. The bulbs require a ballast to start up, and some require a period of time to reach peak light output levels. The recently developed CFL’s are becoming a standard replacement for incandescent, and have an integrated ballast. Dimmable versions have been made available, closing the gap in usability. Fluorescents are good for providing ambient light, but are lacking when it comes to directional or high intensity needs.

Tubo 3 lt Medium Pendant

Fluorescent Fixtures

Tubo- This cleanly minimal fixture uses opal glass to diffuse and warm the gentle glow of a fluorescent T5 bulb.
Eurofase supplies an array of recessed, flush mount, and outdoor fixtures that utilize CFL and fluorescent bulbs.

 

 

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LED Bulbs

Developing from humble beginnings as faintly lit indicator lights on electronics, the LED has seen an explosion of development in recent years. Most of the current boom began with the development of white/blue light spectrum and high intensity LED bulbs. Boasting long life (beating out even fluorescents) and unmatched efficacy (matched only by induction lights-see below) LED’s are quickly becoming the fastest growing sector in the lighting business. The solid state light is also durable and easy to manufacture, meaning after R&D costs are recouped by companies, the high price they currently command will quickly become more reasonable.

The main drawback to LED’s is the linear nature of their light. LED’s make great recessed and directional lights, but challenges regarding diffuse light have been the focus of many creative ideas. Diffusers and arrays can mitigate much of the directional limitations of LED’s, and many innovations are still on the way. With the bulk of R&D funding going to LED and OLED development, this technology will continue to see growth, reduced cost, and innovation.

Viper 7 lt LED Chandelier

LED Fixtures

Viper- Elegant glass forms with pure white light to accentuate the undulating curves of the glass. As the focus on the form the neutrality of the light’s color helps to support instead of distract.

Eurofase is currently expanding its LED fixture offerings. Some fixtures to check out are the Pearla, and the plethora of new flush mounts such as the Alma, Wilson, Dallner, andRamata.

* Above documents are from Eurofase

The color temperature of a light source is the temperature of an ideal black body radiator that radiates light of comparable hue to that of the light source. Color temperature is a characteristic of visible light that has important applications in lighting, photography,videography, publishing, manufacturing, astrophysics, horticulture, and other fields. In practice, color temperature is only meaningful for light sources that do in fact correspond somewhat closely to the radiation of some black body, i.e. those on a line from reddish/orange via yellow and more or less white to blueish white; it does not make sense to speak of the color temperature of e.g. a green or a purple light. Color temperature is conventionally stated in the unit of absolute temperature, the kelvin, having the unit symbol K.

Color temperatures over 5,000K are called cool colors (bluish white), while lower color temperatures (2,700–3,000 K) are called warm colors (yellowish white through red).^[1] This relation, however, is a psychological one in contrast to the physical relation implied by Wien's displacement law, according to which the spectral peak is shifted towards shorter wavelengths (resulting in a more blueish white) for higher temperatures.

Categorizing different lighting

The color temperature of the electromagnetic radiation emitted from an ideal black body is defined as its surface temperature in kelvin, or alternatively in mired (micro-reciprocal kelvin).^[4] This permits the definition of a standard by which light sources are compared.

To the extent that a hot surface emits thermal radiation but is not an ideal black body radiator, the color temperature of the light is not the actual temperature of the surface. An incandescent lamp's light is thermal radiation and the bulb approximates an ideal black body radiator, so its color temperature is essentially the temperature of the filament.

Many other light sources, such as fluorescent lamps, or LED's (light emitting diodes) emit light primarily by processes other than thermal radiation. This means the emitted radiation does not follow the form of a black body spectrum. These sources are assigned what is known as a correlated color temperature (CCT). CCT is the color temperature of a black body radiator which to human color perception most closely matches the light from the lamp. Because such an approximation is not required for incandescent light, the CCT for an incandescent light is simply its unadjusted temperature, derived from the comparison to a black body radiator.

The Sun[edit]

The Sun closely approximates a black body radiator. The effective temperature, defined by the total radiative power per square unit, is about 5,780 K.^[5] The color temperature of sunlight above the atmosphere is about 5,900 K.^[6]

As the Sun crosses the sky, it may appear to be red, orange, yellow or white depending on its position. The changing color of the sun over the course of the day is mainly a result of scattering of light, and is not due to changes in black body radiation. The blue color of the sky is caused by Rayleigh scattering of the sunlight from the atmosphere, which tends to scatter blue light more than red light.

Daylight has a spectrum similar to that of a black body with a correlated color temperature of 6,500 K (D65 viewing standard) or 5,500 K (daylight-balanced photographic film standard).

For colors based on black body theory, blue occurs at higher temperatures, while red occurs at lower, cooler, temperatures. This is the opposite of the cultural associations attributed to colors, in which "red" is "hot", and "blue" is "cold".

*** Contents are from wikipedia.org

Color temperature applications

Lighting

Color temperature comparison of common electric lamps

For lighting building interiors, it is often important to take into account the color temperature of illumination. For example, a warmer (i.e., lower color temperature) light is often used in public areas to promote relaxation, while a cooler (higher color temperature) light is used to enhance concentration in offices.^[8]

CCT dimming for LED technology is regarded as a difficult task, since binning, age and temperature drift effects of LEDs change the actual color value output. Here feedback loop systems are used for example with color sensors, to actively monitor and control the color output of multiple color mixing LEDs.^[9]

Aquaculture[edit]

In fishkeeping, color temperature has different functions and foci, for different branches.

• In freshwater aquaria, color temperature is generally of concern only for producing a more attractive display.^{[citation needed]} Lights tend to be designed to produce an attractive spectrum, sometimes with secondary attention to keeping plants alive.

• In a saltwater/reef aquarium, color temperature is an essential part of tank health. Within about 400 to 3000 nanometers, light of shorter wavelength can penetrate deeper into water than longer wavelengths (see Electromagnetic absorption by water),^[10][11][12] providing essential energy sources to the algae hosted in (and sustaining) coral. This is equivalent to an increase of color temperature with water depth in this spectral range. Because coral, typically living in shallow water, receives intense, direct tropical sunlight, the focus was once on simulating this with 6,500 K lights. Higher temperature light sources have become more popular, first with 10,000 K and more recently 16,000 K and 20,000 K.^{[citation needed]} Meanwhile, actinic lighting is used to make the somewhat fluorescent colors of many corals and fish "pop", creating brighter "display" tanks.

Digital photography[edit]

In digital photography, color temperature is sometimes used interchangeably with white balance, which allow a remapping of color values to simulate variations in ambient color temperature. Most digital cameras and RAW image software provide presets simulating specific ambient values (e.g., sunny, cloudy, tungsten, etc.) while others allow explicit entry of white balance values in kelvins. These settings vary color values along the blue–yellow axis, while some software includes additional controls (sometimes labeled tint) adding the magenta–green axis, and are to some extent arbitrary and subject to artistic interpretation.^[13]

Photographic film[edit]

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Photographic emulsion film sometimes appears to exaggerate the color of the light, as it does not adapt to lighting color as human visual perception does. An object that appears to the eye to be white may turn out to look very blue or orange in a photograph. The color balance may need to be corrected while shooting or while printing to achieve a neutral color print.

Photographic film is made for specific light sources (most commonly daylight film and tungsten film), and used properly, will create a neutral color print. Matching the sensitivity of the film to the color temperature of the light source is one way to balance color. If tungsten film is used indoors with incandescent lamps, the yellowish-orange light of the tungsten incandescent lamps will appear as white (3,200 K) in the photograph.

Filters on a camera lens, or color gels over the light source(s) may also be used to correct color balance. When shooting with a bluish light (high color temperature) source such as on an overcast day, in the shade, in window light or if using tungsten film with white or blue light, a yellowish-orange filter will correct this. For shooting with daylight film (calibrated to 5,600 K) under warmer (low color temperature) light sources such as sunsets, candlelight or tungsten lighting, a bluish (e.g., #80A) filter may be used.

If there is more than one light source with varied color temperatures, one way to balance the color is to use daylight film and place color-correcting gel filters over each light source.

Photographers sometimes use color temperature meters. Color temperature meters are usually designed to read only two regions along the visible spectrum (red and blue); more expensive ones read three regions (red, green, and blue). However, they are ineffective with sources such as fluorescent or discharge lamps, whose light varies in color and may be harder to correct for. Because it is often greenish, a magenta filter may correct it. More sophisticated colorimetry tools can be used where such meters are lacking.

Desktop publishing[edit]

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In the desktop publishing industry, it is important to know a monitor’s color temperature. Color matching software, such as Apple's ColorSync for Mac OS, will measure a monitor's color temperature and then adjust its settings accordingly. This enables on-screen color to more closely match printed color. Common monitor color temperatures, along with matching standard illuminants in parentheses, are as follows:

• 5,000 K (D50)
• 5,500 K (D55)
• 6,500 K (D65)
• 7,500 K (D75)
• 9,300 K.

D50 is scientific shorthand for a standard illuminant: the daylight spectrum at a correlated color temperature of 5,000 K. Similar definitions exist for D55, D65 and D75. Designations such asD50 are used to help classify color temperatures of light tables and viewing booths. When viewing a color slide at a light table, it is important that the light be balanced properly so that the colors are not shifted towards the red or blue.

Digital cameras, web graphics, DVDs, etc., are normally designed for a 6,500 K color temperature. The sRGB standard commonly used for images on the Internet stipulates (among other things) a 6,500 K display whitepoint.

TV, video, and digital still cameras[edit]

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The NTSC and PAL TV norms call for a compliant TV screen to display an electrically black and white signal (minimal color saturation) at a color temperature of 6,500 K. On many consumer-grade televisions, there is a very noticeable deviation from this requirement. However, higher-end consumer-grade televisions can have their color temperatures adjusted to 6,500 K by using a preprogrammed setting or a custom calibration. Current versions of ATSC explicitly call for the color temperature data to be included in the data stream, but old versions of ATSC allowed this data to be omitted. In this case, current versions of ATSC cite default colorimetry standards depending on the format. Both of the cited standards specify a 6,500 K color temperature.

Most video and digital still cameras can adjust for color temperature by zooming into a white or neutral colored object and setting the manual "white balance" (telling the camera that "this object is white"); the camera then shows true white as white and adjusts all the other colors accordingly. White-balancing is necessary especially when indoors under fluorescent lighting and when moving the camera from one lighting situation to another. Most cameras also have an automatic white balance function that attempts to determine the color of the light and correct accordingly. While these settings were once unreliable, they are much improved in today's digital cameras, and will produce an accurate white balance in a wide variety of lighting situations.

Artistic application via control of color temperature[edit]

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The house above appears a light cream during the midday, but seems a bluish white here in the dim light before full sunrise. Note the different color temperature of the sunrise in the background.

Video camera operators can white-balance objects which aren't white, downplaying the color of the object used for white-balancing. For instance, they can bring more warmth into a picture by white-balancing off something light blue, such as faded blue denim; in this way white-balancing can serve in place of a filter or lighting gel when those are not available.

Cinematographers do not "white balance" in the same way as video camera operators; they can use techniques such as filters, choice of film stock, pre-flashing, and after shooting, color grading (both by exposure at the labs and also digitally). Cinematographers also work closely with set designers and lighting crews to achieve the desired effects.

For artists, most pigments and papers have a cool or warm cast, as the human eye can detect even a minute amount of saturation. Gray mixed with yellow, orange or red is a "warm gray". Green, blue, or purple, create "cool grays". Note that this sense of temperature is the reverse of that of real temperature; bluer is described as "cooler" even though it corresponds to a higher-temperature black body.

"Warm" gray	"Cool" gray
Mixed with 6% yellow.	Mixed with 6% blue.

Lighting designers sometimes select filters by color temperature, commonly to match light that is theoretically white. Since fixtures using discharge type lamps produce a light of considerably higher color temperature thantungsten lamps, using the two in conjunction could potentially produce a stark contrast, so sometimes fixtures with HID lamps, commonly producing light of 6,000–7,000 K, are fitted with 3,200 K filters to emulate tungsten light. Fixtures with color mixing features or with multiple colors, (if including 3,200 K) are also capable of producing tungsten like light. Color temperature may also be a factor when selecting lamps, since each is likely to have a different color temperature.^[14]

* Above good text are from wikipedia.org

The "color" of light sources is derived from a complicated relationship derived from a number of different measurements, including correlated color temperature (CCT), color rendering index (CRI), and spectral distribution. In general, color is most accurately described by a combination of CCT and CRI.

Correlated Color Temperature (CCT)
The first factor in choosing a lamp color is the correlated color temperature. For example, if a retailer wants lighting to blend in with warm halogen accent lamps, the retailer may choose a Venture® MP 100W/C/U/3K, which has a correlated color temperature of 3200K. CCT is defined as the absolute temperature (expressed in degrees Kelvin) of a theoretical black body whose chromaticity most nearly resembles that of the light source. The CCT rating is an indication of how "warm" or "cool" the light source appears. The higher the number, the cooler the lamp color will appear. The lower the number, the warmer the lamp color will appear.

Spectral Energy Distribution
When we look at a light source, the eye "perceives" a single color. In reality, we are seeing literally thousands of colors and hues made up of a combination of different wavelengths of light. These different combinations and the relative intensity of various wavelengths of light are used to determine the CRI of a light source.

Color Rendering Index (CRI or Ra)

In general, CRI is a numeric indication of a lamp’s ability to render individual colors accurately relative to a standard. The CRI value is derived from a comparison of the lamp’s spectral distribution to the standard (e.g. a black body or the daytime sky) at the same color temperature. 

Color Shift and Variation
Different colors are produced in metal halide lamps by using various arc tube shapes and metal halide salts. In new lamps these halides need to "burn-in" for approximately 100 hours before they reach their optimum color. This is why new lamps can sometimes be unstable or vary in color.

As metal halide lamps age, chemical changes occur causing shifts in color. Generally, traditional probe start lamps shift approximately twice as much in CCT over life compared to Uni-Form® pulse start lamps. 

Special Colors:
Designer Color® lamps that produce blue, green, aqua and pink light are available for special applications where color is needed without light loss due to filters.

Different Colors
Venture Lighting offers lamps in many colors to suit virtually any lighting application. Outlined below are the various color temperatures (CCT) currently available:

27K 2700K - Used as a replacement for very warm incandescent lamps (coated only).

3K 3000K-3200K - Used as a general warm, white light source, available in clear or

coated finish for retail or interior applications; blends with halogen lamps.

4K 3700K-4000K - Used as a neutral white light source, available in clear or coated finish for general lighting, factories, parking lots, warehouses.

5K 5000K - A moderately high CCT daylight source used in general and retail lighting applications

6K 6500K - A high CCT daylight source used to simulate average outdoor light conditions

10K 10,000K - A very high CCT, daylight light source, used in horticulture and aquarium applications.

Open or Enclosed
All ratings based on the use of a 9000 lumen rated 100 watt metal halide, vertically oriented lampin a commercially available 8" aperature, black baffled downlight.

Light Output 
The lumen output values at specific hours of lamp life can be measured and plotted. This lumen maintenance (or lumen depreciation) curve contains important data for lighting designers. Though initial lumen ratings at 100 hours are frequently the basis for comparing light sources, mean lumens, determined at 40% of rated lamp life, are the most important. Mean lumen ratings are based on the lamps operating at 10 hours per start (except where noted). Lamp lumens are measured on a reference ballast in the designed operating position at the rated lamp wattage.

Lumen maintenance curves represent the lamp manufacturer’s estimate of the best lamp lumen output plotted over time. Typically, each group of lamps tested will display a range or scatter of lumen maintenance values at each interval measured. Therefore, individual lamps may vary from published mean lumen ratings.

Many factors affect the performance of metal halide lamps over time. Most of these factors (see table) are controllable in the design of the lighting system. Incorporating as many of the optimized conditions as possible will deliver the best performance from any given metal halide lighting system. More light reducing conditions present in the design of the lighting system create a gap between published "optimized" ratings and actual lighting system performance.

For example, Venture’s Uni-Form® pulse start lamp operated on an a low current crest factorSingle Voltage Hybrid or HX magnetic ballast, and other optimized conditions, can be expected to deliver mean lumens approaching 80%. In contrast, astandard metal halide system operating under light-reducing conditions may deliver only 50% lumen maintenance. Venture Lighting publishes "optimized mean lumens."

Even within the Uni-Form pulse start system, you can expect a range of lumen maintenance from 70% to 80%. (see chart below) Performance will vary depending on the number of light-reducing conditions present. By selecting a Uni-Form pulse start lamp, a low current crest factor Single Voltage Hybrid or HX magneticballast, and optimizing the system conditions, significant improvements in lighting system performance can be achieved

.

Studies on nighttime visibility demonstrate experimentally that the sensitivity of the human eye to different colors of light at various light levels determines the true, or effective, lumen output of a lamp. Recent research shows that the color output of the light source has a significant effect on nighttime visibility, which is important because road accidents occur mostly at night. Also, it is well known that the eye responds to color depending upon the amount of light availab

le.

Photopic, Scotopic And Mesopic Conditions
Lumens are the standard measure of light output, but light is actually defined as energy evaluated by the eye. Standard lumen measurements define the light output response of a person only during high light levels (called photopic light), typical of daylight and interior lighting. The light meter measures photopic light as seen by the central region of the eye.

When light levels are very low, like starlight, the viewing conditions are referred to as "scotopic." Under these conditions, the eye’s visual response changes dramatically. Sensitivity to yellow and red light is greatly reduced, while response to blue light is vastly increased. If lamp lumens under scotopic viewing conditions have been determined using photopic measurements, the lumen value does not accurately measure the true amount of light production as perceived by the human eye.

The eye response does not shift suddenly from high light levels to low light levels. A gradual change occurs as light levels are reduced in twilight and typical street lighting conditions. This is the "mesopic" condition in which the eye’s response lies somewhere between photopic and scotopic.

Rods And Cones
The change in the eye’s spectral response is due to the presence of two types of light receivers in the retina, called rods and cones. Rods are responsible for human vision at low light levels and are located in the peripheral field of view. Conversely, only objects viewed directly by the eye are seen by the cones. Rods are sensitive to scotopic light; cones react to photopic light. Therefore, as the light level is reduced, cones become less active and rods become more active. 

Eye Color Sensitivity And Lumens
The value of a lamp’s lumen output is different when considering the shifting color sensitivity of the eye at low light levels. The effective lumens will be different from the measured photopic lumens. As light diminishes from photopic to scotopic conditions, the effective lumens of yellow HPS light sources are reduced and the effective lumens of white light with blue/green content increases. 

This effect is dramatic for low pressure sodium (LPS) lamps. Almost all energy output from this lighting system is yellow, resulting in high photopic lumen output. At low light levels, the effectiveness of LPS lamps is drastically reduced.

Metal Halide Lamps For Low Light Levels
A typical metal halide lamp has strong light output in the blue, green and yellow areas, resulting in high lumen output at all light levels. The blue light output of metal halide is in the high sensitivity region of the eye for low light levels. This means that the effective lumens actually increase for a metal halide lamp as the light level reduces and the eye shifts to a blue/green peak sensitivity. 

The ability to detect fine contrast is also significantly better under metal halide sources than sodium. Reaction time under LPS and HPS lighting is roughly 50% longer than for metal halide. Therefore, the color output of a light source has an important influence on safety. Studies have shown that metal halide lighting, in some circumstances, can be up to six times as effective as HPS. This can make a difference in peripheral viewing and dark areas where hidden hazards may be present.

Proper Use of Metal Halide Lamps
It is imperative that users adhere to specified luminaire and lamp operating positions and requirements. The operation of lamps in positions other than those specified can result in severe reductions in lamp performance, including lamp life, light output and color. Incorrect operating positions can also create the possibility of an early failure.

Refer to each lamp’s technical data specification sheet to determine correct operating position and luminaire requirements. Also, refer to the diagram in this section to determine allowable operating positions.

Lamp Life
Lamp life is an important consideration when purchasing a new, retrofit or replacement lamp. Two very different and distinct terms describe life: "rated life" and "economic life."

Rated Life

Rated, or average (median), life for metal halide lamps is a value of lamp life expectancy based on laboratory and field tests of representative lamps, operating on approved ballasts, with a burn cycle of at least 10 hours per start. The average life is determined when 50% of traditional metal halide lamps initially installed are still operating.

Various operating conditions affect lamp life. One key factor is operating position. Position-oriented lamps (designed to operate in one specific position) are tested and rated based on that designated position. Operating these lamps in any other positions can dramatically shorten life, reduce lumen output and cause color shift. Lamps designated universal can be operated in any position. However, life expectancy and lumen output are sacrificed in certain positions. Published "rated life" for universal lamps is based on operation in the vertical position. "Rated life" for universal lamps operated horizontally is 75% of the published rating.

Economic Life

Economic life refers to the hours of operation during which a lamp is designed to provide optimum light output and color quality as well as lowest replacement cost. Economic life describes actual lamp life better than rated life because rated life does not account for the lumen depreciation and color shift that occur as lamps age. The economic life of lamps is generally 60% to 75% of the lamp rated life. Though economic life is important when considering a lighting system, lamp data tables show rated life because they provide a comparison with other lamp manufacturers’ ratings.