Product Review: Nipple Orientation of Metal Halide Bulbs Revisited

Nipple Nonsense,” an
article I wrote for the first issue of Advanced Aquarist
was an attempt to systematically examine a discussion topic that
had recently made the rounds of on-line discussion groups. It
explored the notion that the position of the nipple, the small
piece of glass on the inner envelope that remains when the
envelope is sealed, makes a difference in the performance of
single ended metal halide bulbs. The article produced quite a bit
of discussion. Numerous individuals came forward with logical
explanations for why the nipple orientation of a metal halide
bulb does matter. Several people took me to task for what they
perceived to be flaws in my methodology. A handful of hobbyists
came forward to say that they themselves had experienced bulbs
changing color just by virtue of reorienting the nipple. Given
the interest in the subject, the editor of Advanced
decided that I should look a little more closely at
the phenomenon. The following report is based on additional work
completed after the publication of the first report. Readers
unfamiliar with the controversy should first read Part 1 (Jan
2002 issue).


Two German 10,000 K bulbs, one with the
support wire on the same side as the nipple, a second nearly
identical bulb with the support wire on the opposite side.

Most of the hobbyists reporting problems use single ended
German 10,000 K bulbs in the 175 watt or 400 watt size. There are
a number of bulbs referred to as “German 10K” so one
uncertainty is whether everyone reporting a difference is using
the same bulbs. I decided to examine the most common German
10,000 K bulbs, the Aqualine Buschke and Ushio bulbs. (AB has
distributed different 175 watt bulbs over the years. I examined
only the AB bulb that is physically similar to the Ushio brand
bulb.) For many years hobbyists from around the country have
given me used bulbs to evaluate so I had several bulbs of varying
burn hours to test. These bulbs have been used on different
ballasts by different hobbyists, and the hours burned are
estimates provided by the hobbyists, but testing a cross-section
of used bulbs offered the best chance of reproducing the
experiences of those reporting a problem. To compare used bulbs
to a new bulb, new Ushio bulbs were seasoned according to IES
protocol and also evaluated.


Before proceeding it should be pointed out that this second
round of testing differed from the testing for the first article
and was specifically designed to better recreate the conditions
under which hobbyists reported a change in apparent color of the
light generated by the bulbs. In the first report the bulbs were
held steady and the sensors moved. For these additional tests the
sensor was kept below the bulb (where the tank would be) and the
bulb rotated. Two sets of measurements were taken, one set with
the nipple pointing up away from the sensors and a second set
with the nipple pointing down towards the sensors. The bulbs were
mounted in a bare horizontal free-standing socket with no
reflector well away from any reflecting materials. The socket
could be rotated so that the bulbs could be reoriented with a
minimum of effort. Ambient light level in the room was checked
between tests and at no time exceeded 1 uE/m^2/sec during
testing. Each bulb was monitored while it warmed until it had
stabilized as indicated by a steady PAR reading, and only then
were final measurements taken. After each bulb was tested it was
allowed to cool to room temperature in the same position. The
bulb was then removed and replaced with the next bulb to be
evaluated. All bulbs were tested in one orientation and then the
sequence was repeated in the other orientation. The 175 watt
bulbs were tested with an IceCap electronic ballast optimized for
German bulbs. The 400 watt bulbs were tested with a PFO HQI
ballast. The sensor was rigidly mounted in a frame placed below
the bulb and the distance between sensor and bulb was set at 18
inches. While my primary interest was in color temperature,
intensity or PAR was also measured. Spectral measurements were
also taken (data not shown).


Table one below shows intensity and color temperature for each
175 watt bulb in each orientation. The bulbs are designated by
the hours reportedly burned. The construction column refers to
whether the bulb has a support wire running along the envelope on
the same side as the nipple (designated with an “s”) or
a support wire on the opposite side of the envelope. These are
designated with an “o”.

BulbPARColor temp Construction

(see text)

1500 hrs74.857.76,3606,530o
2700 hrs59.239.354305430s
2900 hrs39.163.947104760o
3700 hrs51.556.168005710s

A bulb with just a few hours on it has a
nearly clear inner envelope.

There is a measurable difference between the intensity in one
orientation and the intensity in the other. However, nipple
orientation is not a useful predictor of which orientation
generates more light. In some cases the nipple side produced more
light and with others the side opposite the nipple produced more
light. As it turned out, the orientation of the support wire was
a better predictor of which orientation produced more light at
the sensor. The color temperature of the bulbs varied somewhat
from orientation to orientation, but the differences were quite
small in all but one case. None of the bulbs took on a
“yellow cast” as reported by hobbyists.


I have fewer samples of 400 watt German 10,000 K bulbs. Three
were evaluated, two used and one seasoned new bulb. Table 2 shows
the results.

BulbPARColor tempConstruction (see text)
1000 hrs144.9160.88,5009,520o
3700 hrs88.2150.18,3308,470o

In the case of the 400 watt bulbs, all three produced the
highest intensity and color temperature with the nipple pointed
down towards the sensor. The difference in intensity between
orientations was substantial, but the difference in color
temperature would probably be too small to visually detect.


In several attempts, I was unable to recreate the color shift
phenomenon reported by hobbyists. There were minor differences in
color temperature depending on nipple orientation, but the
differences would probably be too slight to be visible. In
addition to the tests outlined above, I also reoriented warm
bulbs to see if the orientation while cooling made a difference.
It did not. I also borrowed a bulb from one of the hobbyists
reporting the problem and was unable to recreate the color
change. The hobbyist himself was unable to recreate the color
shift when he put the bulb back in service.


After several months of use, deposits build
up inside the envelope reducing intensity.

There are hobbyists that are convinced that orientation
matters and insist that they have observed the effect themselves.
We also have hobbyists that are equally convinced that regardless
of their bulbs’ orientation they produce the same color of
light. Given the number of variables involved in lighting
including the type of bulb, the age of the bulb, the ballast,
wiring, and the hostile environment of a reef tank, both groups
are probably correct. Under certain sets of circumstances it
might be possible for some metal halide bulbs to appear yellow.
Furthermore, reorienting the bulb may change the color of the
light. However, with the data gathered so far, it is difficult if
not impossible to predict under what circumstances and conditions
this might occur let alone determine whether reorienting the bulb
will solve the problem.

The issue of light intensity asymmetry is an equally thorny
issue. Part one demonstrated that metal halide bulbs tend to
produce higher intensity above the bulb than below it. These
latest tests measuring intensity only below the bulb show that
some bulbs produce considerably greater intensity in one
orientation than the other. With some bulbs these asymmetries may
be ameliorated by the design of the bulb and the orientation of
it. The Iwasaki bulbs evaluated in part one showed less asymmetry
than the German bulbs evaluated here. This suggests that it may
be difficult to predictably manipulate the light intensity field
by reorienting the bulb unless the specific bulb is evaluated.
And there remains the question of whether we would want more
light reflected into the reflector or more light directed
directly into the tank even if we knew the specific asymmetry of
a bulb. This is a decision that each hobbyist needs to make. As I
stated in the conclusion of part one, given the quasi-point
source nature of metal halide bulbs, it may be better to orient
bulbs with asymmetrical light fields so that more light is
directed into the reflector. This may create a more even light
field in the tank and reduce the possibility of light “hot
spots” directly below the lamps.


  Advanced Aquarist

 Richard Harker

  (14 articles)

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