The Aqualine 150 watt metal halide bulb and fixture
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Last
month we began looking at the Aqualine double ended 150 watt
metal halide bulb and fixture. We found that despite persistent
on-line assertions suggesting that the double ended 150 watt
bulb is as bright as some 400 watt bulbs, we showed that the 150
watt bulb is not as bright as the equivalent single ended 175
watt AB bulb let alone 250 watt or 400 watt bulbs. In this
second part of the Aqualine 150 watt review, we’ll show that
the key element in the AB system is not the bulb, but rather the
reflector. And we’ll show that depending on the needs of the
reef tank, the double ended 150 watt AB system may be a better
choice than the AB 175 watt bulb.
My
February
1999 Aquarium Frontier’s
review of the SpiderLight reflector evaluated the reflector
using a Aqualine 175 watt bulb and tar ballast. We therefore
have a useful metric by which to evaluate the double ended bulb
and fixture. Briefly, the protocol consists of measuring light
intensity every inch (roughly the width of the light sensor)
over a 20 inch by 20 inch grid. The light intensity is then
plotted in a X-Y-Z diagram where the X and Y axes represent of
location of the sensor and the Z axis is the light intensity
(PAR) in uE/sec/m^2. For a complete explanation of the protocol
used for the SpiderLight evaluation, please refer to the Aquarium
Frontier’s review.
The
intensities shown for the 175 watt single ended bulb using a
SpiderLight reflector are directly comparable to the Aqualine
double-ended 150 watt bulb and fixture with one exception. For
the single ended system, intensity was measured over the area
forward of the bulb. Intensity was not measured in the area
directly behind the socket of the bulb. In contrast, light
generated by the double ended fixture was measured over an area
that extended in all directions from the fixture. Consequently,
the diagram shows both negative and positive distances with (0,
0) representing the area directly below the center of the inner
envelope. During the evaluation, line voltage, current drawn,
and power consumed by the system was monitored. The fixture
consumes 210 watts during operation.
Diagram
1 shows the results of the evaluation. The most obvious
difference between the SpiderLight/175 watt system and the
AB/150 watt system is the greater intensity of the 150 watt
system. The highest intensity measured with the 175 watt system
was 54 uE/sec/m^2. And this intensity was measured at a point
well away from the bulb. In contrast, the highest intensity
measured with the 150 watt system was 131 uE/sec/m^2, an
intensity 140% brighter than the 175 watt bulb system generated.
An equally striking difference is the light field generated by
each system. The SpiderLight creates two intense ridges of light
projected some distance from the center of the reflector. The
double ended system’s greatest intensity is directly below the
bulb and light falls off predictably as the distance from the
fixture increases.
Diagram 1
Light
fall-off is also greater with the SpiderLight system. At a
horizontal distance of two feet as measured from the base of the
bulb along the long axis of the bulb, intensity dropped by
two-thirds (68%) from the most intense areas. In contrast, two
feet from the center of the AB system, light has only dropped off
by 27%. Somewhat surprising, light fall-off is fairly symmetrical
with the double ended system. At a distance of ten inches from the
center of the bulb along the axis of the bulb, light intensity has
dropped to 95 uE/sec/m^2. At the same distance perpendicular to
the long axis the intensity has dropped to 88 uE/sec/m^2.
The
double ended system produces more intense light, and equally
importantly, it produces more intense light over a larger area.
All this with a bulb that actually produces less light than its
equivalent single ended brethren. How is this possible? For the
reason outlined in part one of this review: The designer of a
double ended system can maximize light efficiency because the
geometry of the bulb is known. The facets of the reflector can be
specifically tailored to the bulb. In contrast, the designer of a
reflector designed for single ended bulbs has to make certain
assumptions about the geometry of the bulb used and how the
reflector will be used.
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With
the AB system, the reflector is mounted very close to the bulb.
The reflector center ridge that reflects light away from the upper
part of the bulb is just a fraction of an inch from the bulb. This
ridge reflects otherwise lost light to an adjacent facet which
then reflects the light into the tank. With the SpiderLight (as
well as similar reflectors from other companies), light travels
some distance before striking any reflector. The reflected light
must then travel a considerable distance before it strikes the
second facet that directs the light into the tank. The longer
distances the light must travel combined with a more open geometry
accounts for the lower light levels measured with the SpiderLight.
So
which generates more light, an Aqualine double-ended 150 watt bulb
or single ended 175 watt bulb? The short answer is that it
depends. Clearly, Aqualine engineers have done an effective job in
maximizing the light output of the 150 watt fixture. Could a
hobbyist achieve the same efficiencies with a single ended system?
My answer is possibly, with a carefully designed specular
reflector. It is quite unlikely, however, that a hobbyist could
achieve these light levels even with a 400 watt system if little
consideration has been given to the system’s reflector
