![](media/image1.jpeg){width="4.208333333333333in"
height="2.8125in"}**Light Output**

*The Measurement of Lamp Output*

One of the most important considerations in selecting a light source is
how much light it will generate. The unit of measure used for
determining light is the lumen. One lumen equals the amount of light
generated by a single standard candle.

While lumens are a measurement of light output from the light source
(lamp), it only indirectly correlates to how much usable light there is
for a certain application. This is true because visual light is actually
how much illuminance is reflected from the surface(s) it hits. Light can
be absorbed or reflected in different ratios depending on the surface it
touches. This accounts for many other factors involved in lighting an
area such as the type of fixture (reflector) used, how dirty or clean
the fixture is, the total size of the space (room) to be illuminated,
the color (reflectivity) of the walls, floor, and ceiling, among other
factors.

To determine how much light actually illuminates a surface, a different
measurement, foot-candle (fc.), must be used. A foot-candle is 1 lumen
of uniform illuminance over the area of 1 square foot. The metric
equivalent to foot-candles is lux (1 lumen per square meter). To convert
fc. to lux, multiply the fc. by 0.0929. To convert lux to fc. multiply
lux by 10.76.

There are two important measurements used when considering selection of
a lamp: initial lumens and mean lumens. Two measurements are needed
because, like most devices, lamps lose some light output over their
rated life. The gradual loss of efficacy (lumens per watt) is called
lumen depreciation. Lumen depreciation in lamps is caused by two main
factors, loss of chemical additives in the lamp and wall darkening in
the arc tube. In the arc tube are chemicals that are responsible for the
generation of light. As the lamp operates, these chemicals react with
the arc tube components and eventually can no longer produce light.
Also, the standard arc tube contains two tungsten electrodes that are
heated to incandescence during lamp operation. When the lamp is started,
these electrodes evaporate tungsten which deposits on the inside wall of
the arc tube. These black deposits absorb light and cause the amount of
light emitted by the lamp to decrease. Both of these are very gradual
processes, but the end result is a loss in efficacy for the arc tube. In
Venture's new [Uni-Form® pulse
start.](http://www.venturelighting.com/UniformPulseStart/0225-Combined LMC Sht.pdf) 
technology, the unique formed body arc tube lamp provides greater
efficacy and better lumen maintenance than the older, standard pinch
body arc tube technology

*Initial Lumens*

Initial lumens is a term defined as the amount of light output from a
lamp when it is new. For a metal halide lamp, these ratings are averages
based on photometry at rated lamp watts after 100 hours of operation.
Ratings are made after 100 hours to allow the light-producing chemicals
in the arc tube to \"settle in to the correct position in order to
deliver optimum performance. During the first 100 hours, the instability
in chemical location is sometimes seen as rapid shifts in color called
flaring. Also, the light given off by the lamp during the initial 100
hours is up to 20 percent higher than the initial lumen ratings. Both of
these phenomena are normal for metal halide lamps. Both the light output
and flaring will typically stabilize within the first 100 hours.

Universal lamp ratings are based on lamps burning in the base up
position. When universal lamps are burned in positions other than base
up, light output for these lamps can be significantly lower than the
listed ratings. The table below shows how position oriented horizontal
(HOR) lamps outperform universal rated lamps when burned horizontally.

*Mean Lumens*

Lighting designers and specifiers know that any light source will
decrease in light output the longer it is operated (see previous page).
To properly light a facility for the useful life of a lamp, they must
calculate an \"average\" lumen output known as mean lumens. These
ratings are averages based on photometry at rated lamp watts - at 40% of
the [lamp
life](http://www.venturelighting.com/TechCenter/Lamps/lamp_life.htm)
when operated on typical commercial ballasts, and based on the lamps
burning at 10 hours per start (except as noted).

Both burning and measurements are conducted in the designed burning
position (i.e. horizontal or base down). Universal lamps are burned and
measured in the base up position. When a lamp is burned in other than
the design position, mean lumens will be lower than the rated base-up
operation values, and life will be shortened.

*Lumen Maintenance*

The lumens generated by a lamp will decrease as the lamp ages, a factor
known as lumen depreciation. Most often the lumen depreciation that the
user sees is a combination of decreased lamp output and a dirt factor.
Dirt accumulation on the fixture's reflector and lens can greatly
decrease the amount of usable light (in many cases more than lumen
maintenance). This is another reason why [group
relamping](http://www.venturelighting.com/TechCenter/Lamps/group_relamping.htm)
(and cleaning) is critical for maintaining a lighting system. Open
fixture lamps allow the fixture manufacturer to remove the glass lens,
thereby removing a key ingredient for dirt depreciation. Venture
Lighting continually conducts research and testing to ensure they have
the best lumen maintenance possible. Lumen maintenance ratings are based
on 10 burning hours per start (except as noted). Lumens will be lower
for shorter burn cycles (i.e. 6% to 8% lower at 5 hours per start).
Individual lamps may vary from printed mean lumen ratings and the lumen
maintenance curve seen on this page. These are a general guide and refer
to the average for a group of lamps.

![](media/image2.jpeg){width="3.125in"
height="3.9479166666666665in"}**Lamp Color**

One of the most important attributes of metal halide lamps is their
ability to provide crisp white light in a variety of different color
temperatures to accommodate users' needs. High pressure sodium and
mercury lamps are very limited in the color and quality of light they
produce. The colors they generate are often unpleasing or inappropriate
for many applications. This helps explain why the use of metal halide
lamps continues to increase dramatically each year around the world.

The color of light sources is a complicated relationship deriving from a
number of different factors, including Correlated Color Temperature
(CCT), Color Rendering Index (CRI), and spectral distribution.

*Correlated Color Temperature (CCT)*

The first factor in choosing a lamp color is to determine the associated
Kelvin temperature. For example, if a retail store wants accent lighting
to blend in with warm halogen incandescent lamps, they may choose a
Venture MP 100/C/U/27K which has a Correlated Color Temperature (CCT) of
2700 Kelvin. This \"temperature\" is not simply an arbitrary number, but
is correlation with actual thermal temperature. Anyone who has seen a
piece of metal being heated will notice that as the temperature of the
metal increases, the color of the metal changes. This is a rough
explanation

of how the CCT of high intensity discharge and fluorescent light sources
is measured. CCT is defined as the absolute temperature (expressed in
degrees Kelvin) of a theoretical black body whose chromaticity most
nearly resembles that of its light source. From this standpoint, the CCT
rating is an indication of how \"warm\" or \"cool\" the light source is.
The higher the number, the cooler the lamp. The lower the number, the
warmer the lamp.

![](media/image3.jpeg){width="2.8125in" height="2.1145833333333335in"}

*Spectral Energy Distribution*

When we look at a light source, we \"perceive\" a single color. In
reality, we are seeing literally thousands of colors and hues of colors
made up of a combination of different wavelengths of light. These
different combinations, and the relative intensity of various
wavelengths of light, can be used to determine a light source's CRI.

*Color Rendering Index (CRI)*

In general, CRI is an indication of a lamp's ability to show individual
colors relative to a standard. This value is derived from a comparison
of the lamp's spectral distribution compared to a standard (typically a
black body) at the same color temperature.

Incandescent lighting is the only light source that follows a true black
body curve. Other sources (i.e. metal halide) are rated with a
Correlated Color Temperature (CCT). The CCT, however, does not provide
information on the quality of color. For this, a Color Rendering Index
(CRI) is also necessary. In general, the higher the CRI rating of a
lamp, the better different colors will show. However, this guideline can
be misleading with certain lamp types because a high CRI sometimes makes
different colors easier to distinguish, but standard colors may appear
different than they actually are. The following is an example of how the
color \"white\" may appear under different light sources.

  --------------------- --------------------- ---------------------------
  Standard              \"Hylux\"             Color Corrected

  Metal Halide          Metal Halide          White HPS

  4000K                 5500K                 2300K

  CRI - 65              CRI - 90              CRI - 90

  White is              White is              White is

  White                 Bluish-green          Yellow
  --------------------- --------------------- ---------------------------

*Color Shift and Variation*

Different colors are achieved in metal halide lamps by using different
arc tube designs and by introducing various chemicals inside of the lamp
arc tube. New lamps need to have these chemicals \"burn-in\" for
approximately 100 hours before they reach their optimum color and light
level. This is why new lamps can sometimes be unstable or vary in color.

As metal halide lamps age, chemical changes occur in the lamp causing
shifts in the chromaticity of the lamps. Different lamp designs shift in
different ways, and different lamps from the same group may shift in
different amounts. Generally, over economic life lamps will shift 200K
to 300K in color temperature. After economic life, a lamp may change as
much as 500K to 600K. As a group of lamps ages together in a facility,
the lamps will generally shift at the same rate causing very little
color variation from lamp to lamp. However, if new replacement lamps are
introduced into the group of lamps, color differences may be more
noticeable, because the new lamps have not aged and shifted with the
remainder of lamps. This is just one of the reasons why many users of
metal halide lamps prefer to group relamp as opposed to spot relamping.
There are many other advantages to group relamping as outlined in the
section on [group
relamping](http://www.venturelighting.com/TechCenter/Lamps/group_relamping.htm).

*The Different Colors*

The advantage of the many colors of lamps offered by Venture Lighting is
that they can be used in virtually any lighting application. Outlined
below are the various colors currently available:

  ------------------- ---------------------------------------------------
  27K - 2700 Kelvin   Often used as accent lighting to blend in with
                      fluorescent 2700K applications.

  3K - 3200 Kelvin    Used as a primary light source for retail
                      applications.

  3700 Kelvin         Coated lamps. Used where a \"softer\" metal halide
                      light source is desired.

  4000 Kelvin:        Used in general lighting; factories: parking lots,
                      warehouses

  5K - 5500 Kelvin    Daylight lamps: horticulture, aquariums, high color
                      definition.

  Special Colors      Blue, Green, Magenta, Pink, Yellow. Special
                      applications where color is needed without light
                      loss due to filters.
  ------------------- ---------------------------------------------------

**Metal Halide 101**

**Proper Use of Metal Halide Lamps**

*Correct Operation And Cautions For Discharge Lamps*

High intensity discharge lamps require auxiliary equipment (ballasts,
capacitors, ignitors, and/or power supplies) to provide the correct
electrical values for starting and operation. This auxiliary equipment
must meet all electrical specifications outlined by ANSI (American
National Standards Institute). Venture Lighting International will not
be responsible for poor performance, property damage, or personal injury
from lamps operating on unauthorized auxiliary equipment, or from lamps
being operated in a manner inconsistent with their design.

Power should always be turned off and preferably locked out in
accordance with OSHA guidelines whenever installation, removal or
maintenance is performed on lighting systems. Always use safety glasses
and gloves when installing or removing HID lamps. Replacement lamps
should be screwed in firmly, but not with undue pressure, into
appropriate lamp sockets. This will avoid loosening due to vibration.

Scratches on the outer envelope, direct contact with water, or excessive
pressure can cause these lamps to break. If the outer jacket should
break, immediately turn the power off. Do not remove a lamp until it has
completely cooled and replace it with a new *Venture* lamp. Immediately
turn the power off if an outer envelope is broken to prevent injury that
may be caused by ultraviolet radiation from an unjacketed HID lamp.

HID lamps and their arc tubes operate at extremely high temperatures and
may shatter as a result of misapplication, system failure, or other
factors. This type of failure may release extremely hot glass and lamp
parts into the surrounding environment, causing a risk of fire, personal
injury, or property damage. It is imperative for users of HID lamps to
use good judgment and common sense for placement of these lamps, in
anticipation of potential violent failures. In areas susceptible to
contamination by flying glass, where flammable materials are present, or
there is a possibility of personnel injury, users should seek additional
protective measures. In these cases, the user should install Venture
open fixture rated lamps and/or use enclosed fixtures even if the lamp
type does not require this type of fixture.

*Starting and Restarting Characteristics*

When using the proper auxiliary equipment, standard metal halide lamps
will start at an ambient temperature of -30 degrees C (-22 F). Full
light output does not occur when power is first applied to cold metal
halide lamps; there is a time delay of 2 to 4 minutes before lamps reach
90% of their full light output.

Venture's exclusive *Uni-Form* formed body arc tube provides [faster
warm-up and hot
re-](http://www.venturelighting.com/UniformPulseStart/upss_advantage.htm#Faster Warm-up/ Hot Restrike)*strike*
in 60% less time. The external ignitor and the *Uni-Form* formed body
arc tube combine to allow better [starting in colder
conditions](http://www.venturelighting.com/UniformPulseStart/upss_advantage.htm#Cold Starting)[,]{.underline}
down to -40°C. 

After lamps have started, if there is a power interruption of 1/2 a
cycle (1/120th of a second) or more, the lamps may go out and not
restart when power is reapplied. It takes several minutes before an arc
can be re-established by a standard ballast and/or ignitor. The exact
time is dependent on a number of factors including lamp wattage, ballast
and/or ignitor characteristics, ambient temperature, fixture dimensions,
and supply voltage. As with initial starting, several minutes are
required before full light output can be achieved. The time needed to
establish full light output can be as short as 5 minutes and as long as
15 - 20 minutes. In general, the use of ignitors and/or special ballasts
will dramatically decrease the time for hot restart. See chart on
ballast characteristics.

**Metal Halide v. Incandescent**

*Economics*

Metal halide is almost always the cost effective solution for general
lighting when compared to incandescent lighting technology. Incandescent
is often selected for applications where instant light output is
required or where only modest light levels or very small bulb sizes are
required. Incandescent is also specified because of its low initial
cost, since it requires no ballasting and the lamps are less expensive.
However, initial cost is not usually a good criteria since the
relatively low efficacy of the incandescent system makes it one of the
costliest to operate. Metal halide is 3 to 5 times more efficient than
incandescent; therefore, the higher initial cost of the metal halide
system is quickly repaid relative to the cost of operation for an
incandescent system. Although incandescent and metal halide are compact
white light sources offering the user substantial versatility in terms
of product selection and utilization, the main difference between the
two technologies is the efficiency with which they generate light*.*
Metal halide has a substantial efficacy edge over incandescent which
often makes it the economic choice.

*The Environment*

When the choice is between metal halide and incandescent lighting, metal
halide is the clear winner for the environment. A 100 watt metal halide
lamp provides 5 times the lumen output of a 100 watt incandescent bulb.
Added to this is the fact that it will burn for an average of 15,000
hours or approximately 15-20 times the life of the incandescent lamp. In
addition to higher operating costs, the incandescent system has greater
adverse impact on the environment.

**Metal Halide vs. Fluorescent**

*Metal Halide Advantages*

Metal halide lamps are highly compact white light sources. Linear
fluorescent lamps, on the other hand, are low brightness sources with
relatively large surface areas. This means that metal halide lamps
radiate much more light per square centimeter of surface area than do
fluorescents. A fluorescent lamp at the highest output has only the
total lumen output of a 175 watt metal halide lamp.

Metal halide lamps offer the user a high light level using smaller, very
compact fixture designs that deliver high light levels. They lend
themselves well to applications where the light needs to be directed or
controlled. This ability to direct light produces better light where it
is needed and gives rise to more dramatic lighting effects. The
inherently higher lumen packages allow the designer to achieve
reasonable illumination levels in high ceiling applications.

Fluorescent light sources can be thought of as belonging to two
different product families, standard linear fluorescent and compact
fluorescent. Standard linear fluorescent does not provide the compact
size of metal halide. This source is good for general diffuse lighting,
but is hard to direct. Compact fluorescent lamps are small, but their
lumen output is somewhat limited.

A major drawback to fluorescent for general lighting is the temperature
sensitivity of the lamps with regard to light output. Fluorescent lamps
operate well over a relatively narrow range of temperatures and are best
for indoor lighting applications where the ambient temperature can be
well controlled. The fluorescent lamp is designed to perform optimally
at around 70ºF (21C) and will experience measurable decline in efficacy
on either side of this optimum. For this reason, fluorescent lamps use
in outdoor applications is much more limited than either incandescent or
high intensity discharge sources.

Metal halide lamps, however, are well suited for both indoor and outdoor
applications and are relatively unaffected by large changes in ambient
temperature.

Metal halide lamps are commonly available today in wattages from 32 up
to 2000 watts, with corresponding lumen packages of 2,000 to 210,000.
Common fluorescent lamp wattages range from 5 to 215 watts, with
corresponding lumen packages of 250 to 15,700. Higher wattage
fluorescent lamps are simply too large to be practical.

Metal halide is best suited to those applications that require higher
foot-candles and where the lamps are more than 8 - 10 feet from the work
surface.

**Metal Halide vs. High Pressure Sodium**

Metal halide lighting differs from High Pressure Sodium (HPS) in the
color and quality of light delivered. Metal halide is a highly efficient
light source capable of delivering a white light in the range of 2700 to
5500 Kelvin with typical CRIs in the mid-60s to mid-70s. Some lamp
chemistries even obtain CRIs in the 80s. In contrast, high pressure
sodium lamps yield yellow lighting (2200K) and have a very poor color
rendering index of 22.

HPS lamps are available in color-corrected versions that shorten their
life and only slightly improve color temperature. Even with greatly
improved CRIs, the color temperature still delivers yellow light. This
color limitation is present because the HPS lamp generates light through
the excitation of sodium. Metal halide lamps, on the other hand,
generate light through the excitation of 2 to 5 different chemicals in
the arc tube. In addition, the exclusive *Uni-Form* formed body arc tube
is a newly-designed, compact light source sculpted to follow the
physical shape of the arc itself. The precise geometry of this unique
arc tube, accurately reproducible from lamp to lamp, produces a metal
halide lamp of greater efficiency, improved color uniformity, and longer
life.

By varying the blend of chemicals in the arc tube, metal halide
engineers are able to alter the characteristics of the light output.
This flexibility in design makes metal halide so versatile. White light
is a very important attribute of metal halide technology, because it is
the closest to the natural sunlight that people prefer.

A number of independent research projects compare each option under low
light levels and provide solid, reliable information to support the
concept that the color of light strongly influences human perception. In
fact, the sensitivity of the eye to different colors determines the true
or effective lumen output of a lamp. The visual effectiveness of white
metal halide light with a high blue/green content is shown to increase
in reduced light while it decreases for the yellow light of sodium
sources.

High pressure sodium has been used for years in less color critical
applications such as parking lot and roadway lighting. Applications more
sensitive to color have used metal halide. The availability of lower
wattage metal halide lamps and the revolutionary *Uni-Form* pulse start
system technology has greatly increased its application in indoor and
outside commercial and industrial environments. Many applications, such
as security and parking garage lighting, now use metal halide instead of
HPS. HPS is used today mainly in areas where color temperature and color
rendition are less important (i.e. warehouses, street lighting, security
lighting). Metal halide is applicable in a wide range of commercial,
industrial and municipal spaces and offers an excellent quality of
light.

Studies show that people generally prefer to work and live in a white
light environment, a fact that itself explains the dramatic shift toward
metal halide.

![](media/image4.jpeg){width="3.4895833333333335in"
height="2.34375in"}**Group Relamping**

Lumen depreciation, color shift over life and cost reduction are the
main reasons that a user should consider a group relamping program. When
a lighting installation is new, the light level is high and the quality
of the light is excellent. Over life, lamps suffer a decrease in
efficacy (lumens per watt) caused by both the loss of the light
producing chemicals within the arc tube and darkening of the inner walls
of standard arc tubes. Most metal halide lamps will decrease to around
60% of initial rated light output at about half of rated life. The
*Uni-Form* formed body arc tube lamp provides greater efficacy and
better [lumen
maintenance](http://www.venturelighting.com/UniformPulseStart/0225-Combined LMC Sht.pdf)
than the older, standard pinch body arc tube technology.

In standard metal halide technology, not only is there a decrease in the
amount of light generated over life, but the quality of the light also
changes. The color of a metal halide lamp is made up of hundreds of
spectral line emissions from the chemicals within the arc tube. This
plot of the lines of color the lamp emits is called its spectral
distribution. It is this collection of colored lines that our eye
interprets as a \"white\" light.

You might remember holding up a prism to the sunlight and seeing the
rainbow of colors produced. The prism is able to break down the sunlight
into all of its many spectral components. Even though sunlight has all
of these component spectral lines, our eyes, together with our brains,
interpret the combination of all these colors as white sunlight. The
same phenomenon is happening when you look at the light produced by a
metal halide lamp.

One difference between sunlight and the light from a metal halide lamp
is that the sun produces the same quality of light at all times. The
differences we see in sunlight are caused by the effects of earth's
atmosphere, not by changes in the sunlight. The metal halide spectral
distribution, however, is not as stable as the sun's. Its spectral
output comes from mercury and metal iodides present in the arc. As the
chemicals are lost to the arc through reactions, the proportions of
their contribution to the spectrum change. Our eye interprets these
changes in spectral distribution as changes in lamp color.

Generally, a metal halide lamp will shift in color by about 200 to 300K
during its economic life. If all the lamps in an installation are
operated in the same fixture type and burning orientation, they will
generally change color in the same direction and amount during economic
life. Therefore, the color shift of the lamps will not be very
noticeable. The problem arises when you spot relamp after economic life.
By then a lamp may have shifted 600K or more causing lamps to appear
bluish, pinkish, or greenish.

With spot relamping, a new, bright white, initial lumen output lamp is
installed in a field of lumen depreciated and slightly color shifted
lamps. The human eye is a wonderful device for comparing color and it,
of course, is able to easily discern that the new lamp is both brighter
and a different color than the old lamps. If you multiply this scenario
over a series of spot relampings, you can see why eventually a metal
halide lighting installation can have quite a non-uniform look.

The answer to this problem is a group relamping program in which the
user relamps the entire installation at one time, usually sometime
between 60% and 70% of rated life. This plan has a number of advantages:

*Cost Effectiveness*

Group relamping greatly reduces spot relamping labor costs because all
lamps are replaced before they reach the point in life where failures
are accelerating. In addition, the cost of energy is by far the largest
portion of maintaining a lighting system. If lamps are not group
relamped, almost half of this energy will be wasted on lamps that are
performing below their designed level. As an example, an average 400
watt metal halide lamp consumes \$800 of energy over its rated life.
About \$320 of these dollars are wasted on lamps not providing optimum
performance. With group relamping, a new lamp and the labor to install
it is generally less than 5% of the total energy cost. Group relamping
also saves downtime because it can be scheduled over a weekend or
shutdown period.

*Aesthetics*

When lamps are of similar light output and color, a lighting
installation looks better. Shopping centers, retail stores and even gas
stations with canopies are retail spaces that are trying to attract
customers. The quality of the lighting says much about the store and the
merchandise. Group relamping maintains the quality of light in a space
infinitely better than spot relamping.

*Improved Light Levels*

An installation that is properly group relamped will have better
maintained light levels than one which is not. Higher light levels have
been associated with increased safety, higher productivity and an
increased sense of security. Since it costs the same amount of energy to
run a fully lumen depreciated lamp as a new lamp of the same wattage,
doesn't it make sense to install the higher lumen output lamp in the
socket?