Analyzing
Reflectors: Part II - Double Ended Lamp Reflectors by
SANJAY JOSHI and TIMOTHY MARKS
Sponsored in part by:
In
Part I of this series [1], we presented the data on 400W single
ended mogul reflectors, designed primarily to be retrofit into
existing canopies. This article continues in a similar vein and
presents the data and analysis of lighting fixtures designed for the
150W and 250W Double Ended (DE) metal halide lamps.DE lamps are now more widely used in the reef aquarium hobby
and are a very popular option for reef lighting applications,
especially for those requiring small overall size or high
efficiencies.Lighting fixtures, or luminaries as they are called in the
lighting industry, for DE lamps are often sold as completely
integrated units with reflectors, sockets, and glass shield mounted
in a housing.The ballast may be remotely mounted or integrated within the
fixture as in the case of the AB-Aqualine Spacelight.One advantage of these fixtures for DE lamps is that they are
often designed very aesthetically and can be used suspended over an
open tank, without the use of a canopy over the aquarium.
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In
Part II of this series, we test a series of double ended lamp reflectors
that were made available to us. Table 1 shows a list of reflectors
examined as well as the lamp and ballast combinations used therein.
Table
1: Listing of the Reflectors Tested
Reflector
Ballast
Lamp
PFO 150W Mini Pendant*
Reliable
Ballast
AB
150W 10000K
AB 150W AquaSpace Light
Integrated
German Magnetic Ballast
AB
150W 10000K
PFO
250W Mini Pendant*
PFO HQI Ballast
AB 250W 10000K
NEW PFO 250W Mini
Pendant
PFO
HQI Ballast
AB
250W 10000K
AB
250W AquaSpace Light
Integrated German
Magnetic Ballast
AB 250W 10000K
Sunlight Supply 250W Reef Optix
III+
PFO
HQI Ballast
AB
250W 10000K
* -
these reflectors have been discontinued and are no longer in production
The
basic methodology and experimental setup is identical to the one used in
the 400W reflector study (ref) and details can be read in the part I of
this series.The data is
also presented in an identical manner with plots for light dispersion
for each reflector at distances of 6, 9 and 12 from the center
of the lamp.
One
critical difference between Part I and this article is the fact that
in Part I, the same lamp and ballast were used with all the
reflectors.This allows for a direct comparison without the influence of
the ballast or lamp as a variable.Because the AB Spacelight fixture features an integrated
ballast and would be used in this configuration we did not try to
remove the ballast that came with it.However we did use the same lamp for the tests.The effect of the ballast hence cannot be completely isolated
from the raw data, but the % dispersion plots presented help
normalize the data with respect to the highest intensity thus
reducing the impact of this variable.The % plot can hence also be used to extrapolate the light
distribution for different ballast and lamp combinations using the
same reflector.Additionally, each of these reflectors is sold with a UV
shielding glass built into the fixture.Each reflector was tested with the glass shield that is sold
with thereflector. The effect due to the difference in the glass
shield cannot be isolated from this data, but once again is captured
within the % distribution plots.
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In
several cases, e.g. the Sunlight Supply and New PFO mini pendants, the
same reflector is used with different holders for 150W and 250W lamps.Since the same reflector is being used we only tested these for
250W lamps, since we expect the results for 150W to be quite similar.
Reflector
Data and Analysis
The
data plots for each reflector at distances 6. 9, and 12 are
plotted as a surface graph, top view graph, and a % distribution graph
to illustrate the intensity and spread at different points on the
measuring grid.Table 2
below shows the list of figures associated with each reflector.
Table
2: List of Figures associated with each reflector
Reflector
Figures
PFO 150W Mini Pendant
Figs.
1-3
AB 150W AquaSpace Light
Figs.
4-6
PFO
250W Mini Pendant
Figs. 7-9
NEW PFO 250W Mini Pendant
Figs.
10-12
AB
250W AquaSpace Light
Figs. 13-15
Sunlight Supply 250W Reef Optix
III+
Figs.
16-18
One
of the measures of a reflector performance could be its ability to
direct light into the aquarium.A
reflectors total incident light upon a surface of a given area is
representative of the performance of a reflector. It is computed by
adding up all the measurements taken at the discrete points within the
region.It demonstrates how much light the reflector is able to focus
downward when compared to other reflectors with similar operating
conditions (same ballast and lamp). Table 3 presents this data for the
reflectors in this article.
Table 3: Total Incident PAR on a
given Surface area
Total
Incident Light
Reflector:
Distance:
3x3
Area
2x2
Area
1x1
Area
Maximum
PAR:
PFO
150W Mini Pendant
6"
13620
13575
12154
1347
9"
13423
13028
9504
701
12"
12778
11568
6900
413
AB
150W AquaSpace Light
6"
21124
20692
16975
2178
9"
20777
18854
12383
1001
12"
19178
15739
8801
542
PFO
250W Mini Pendant
6"
30544
30373
27016
2958
9"
29843
28576
19786
1370
12"
28927
25323
14191
763
PFO
New 250W Mini Pendant
6
41605
41528
39946
4254
9
41421
40770
31426
2310
12
39752
37333
23636
1453
AB
250W AquaSpace Light
6"
43919
42966
34393
4600
9"
41004
36532
22540
1877
12"
37509
29386
15928
863
Sunlight
Supply 250W Reef Optix III+
6"
45326
44911
39202
5428
9"
42482
39513
28244
2123
12"
39298
34523
20804
1176
In
addition to knowing how much light is incident on a given area, we could
also look at how much loss of light occurs on a give area when moving
the lamp and reflector higher.Table
4, presents the % of light lost on a specified area as one move the
lamp/reflector from 6 to 12 above the surface.A higher % loss would indicate that the reflector is creating a
larger spread.
Table 4: Percent of PAR lost from
6 to 12 from the lamp
3x3'
Area
2x2'
Area
1x1'
Area
PFO
150W Mini Pendant
6
15
43
AB
150W AquaSpace Light
9
24
48
PFO
250W Mini Pendant
5
17
47
PFO
New 250W Mini Pendant
4
10
41
AB
250W AquaSpace Light
15
32
54
Sunlight
Supply 250W Reef Optix III+
13
23
47
Another
metric to analyze reflector performance could be to determine the area
coverage of a specified amount of light.Although it is difficult to determine exactly what this specified
minimum PAR values should be, we have chosen a cut off of 500 PARand present the area coverage plots of each of the reflectors in
Figures 19 and 20.
Figure 19
Figure 20
One question that is often asked
of us is which reflector is the best ?.This is not an easy question to answer as it depends on a lot of
variables (shape of tank, height of reflector over the tank, layout of
rock work in the tank, etc.), and keeping in mind the objective you are
trying to achieve.Clearly,
the reflector designs have to balance 2 conflicting requirements
spread v/s intensity.Given
that the total light output for a particular ballast/lamp combination is
fixed (at any instant), it is the reflectors job to direct this
light.A tight focused beam
of light will provide higher intensity over a smaller area, whereas a
dispersed output will provide much larger coverage albeit at a lower
peak intensity.Depending
on your objective whether you want to provide a stron spot light effect
on an area of the reef, or want to broadly light a wide area of the
tank, different reflectors may be more suitable.Also keep in mind that the reflector spread or intensity can be
changed by changing the height at which the reflector is placed above
the surface of the water.The
objective of these articles is to provide data to allow the reef
hobbyist to make an intelligent and informed decision within the
constraints of their application and wallets.Within this focus, we will attempt to provide the data that would
be useful in making an informed choice.
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sponsor of this column
Rather
than focusing on data analysis that any intelligent reader can
garner from the data presented in the figures, we will focus on
the broader issues and implications.The data shows that the AB spacelight, Sunlight Supply
Reef Optix III+, and the New PFO pendant to be good performers as
seen from the figures and the data presented in Table 3 and 4.The numbers are within a few % of each other, and
possibly within the errors of the experimental setup and
measurement.AB
spacelight reflector provides a larger spread of light.The best height for all these reflectors seems to be at
about 9 from the surface of the water.
An
interesting comparison is the one between 250W DE systems and
the 400W lamps reflector systems.Since both used 10000K lamps (although from different
manufactures, and of different styles), we could try to
determine whether we can replace 400W systems with 250W DE
lighting system.This
would be economically quite beneficial to the aquarist, in terms
of savings in power and minimizing heat additions to the tank.Interestingly when comparing the total incident light
over the 3X3, 2X2 and 1X1 areas there is only a slight decrease
in total incident light, while the lamp power is decreased by
37%.Why is there
such a disproportionate difference? One possible explanation
could be that the 400W fixtures are not as efficient as the 250W
DE fixtures the small size of the DE lamp allows for better
reflector design and allows more of the light to get out of the
reflector. With the 400W systems, the larger size of the lamp
envelope may be causing some of the light to reflect back into
the lamp envelope. Another
possible explanation may be that the metric being used (sum of
the total light at all the measured points in the specified
region) is not capturing this correctly.A better metric may be the integration of the volume under
the surface in the intensity distribution graphs.This aspect of the comparison needs to be analyzed
further since it has significant practical implications. For now
we can make this comparison by visually analyzing the graphs
showing the light intensity and distribution.
Conclusion
This
article presents the data and a brief analysis of several
commercially available double ended metal halide lamp
reflectors. The
data provided shows clearly the differences between the
reflectors, and can provide the user with useful data on the
light distribution patterns and shapes, which in turn can be
used for purposes of aquascaping, and placement of corals.The issue of area coverage needs to be addressed in a more
quantitative manner and efforts are currently underway to
determine these areas quantitatively.The computation of the surface integral (intensity X
area) as a means of comparison of reflectors also needs to be
developed further.Future
articles will address this issue, as well as present further
results on some additional horticulture reflector that are
currently being tested.
Acknowledgements
We
would like to thank several people whose help made this study possible.
They were kind enough to provide us with lamps, reflectors and ballasts
for testing: Patrick at PFO Lighting, Brad at Sunlight Supply, and Aqua
Medic.
