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Zoo
Med Powersun Flood Lamp
The
only true flood lamp currently on the market in the UK is
the Zoo Med
Powersun Self-Ballasted Mercury Vapour Flood Lamp. This
is available in 100watt and 160watt versions.
The
100watt Powersun is a small lamp with a semi-opaque phosphor
layer coating a smooth glass face. The 160watt Powersun
is very similar but correspondingly larger.
Both
lamps have standard screw fittings for use in ceramic or
porcelain heat-resistant fixtures. The instructions state
that the lamps must be mounted vertically so that they point
straight down, not at an angle, at a minimum distance of
12”.
We tested
six Zoo Med Powersun 100watt lamps and three Zoo Med Powersun
160watt lamps.
Burning
In
The
process of "burning in" is, in theory, the same
for mercury vapour lamps as it is for fluorescent tubes.
Chemical changes occur in the phosphor and glass, as these
react with one another, and with elements evaporating from
the filaments, under the influence of the ultraviolet light.
The changes make the glass less permeable to UV light and
hence there is a decay in the output of the lamp. This is
normally most rapid during the first few hours of use. After
about 100 hours, all the initial reactions are usually complete
and the decay has slowed right down in most cases.
We burned
in, from new, three 100watt Powersuns and one 160watt Powersun.
We were surprised to find marked differences in the characteristics
of every single lamp, both in their initial output and in
their initial rates of decay. Figure 2 shows the readings,
taken after 90 hours burn, for the four lamps.
The
output of one of the 100watt Powersun lamps was less than
half of the other two at all distances measured; the output
of the 160watt Powersun lamp was a little higher than these
two. The Powersun lamp with the lowest output appeared to
have a slightly thicker, more opaque phosphor coating at
the front of the bulb.
We plotted
the decay for each lamp. The results are shown in Fig. 3.
One of the 100watt Powersuns with the higher initial output
showed almost no decay over the test period; the other lamps
all showed the decay typical of “burning in”, with a greater
loss over the first few hours.
The
160watt Powersun and the three 100watt lamps with higher
output all ended the 105-hour burn emitting between 30-45uW/cm²
at 12”. This exceeds the output of all new fluorescent tubes
except for the Reptisun 10.0, tested without a reflector.
The one lamp with lower output burned in to 15uW/cm² at
12”, which is similar to the output of several older fluorescent
tubes we tested.
We measured
the output of five more Zoo Med Powersun lamps of different
ages; the oldest had been in use for about 11,000 hours
(12 hours a day for two and a half years) and was still
emitting 10uW/cm² at 12”. We burned one of the 100watt lamps
for a total of 250 hours and took a further set of readings.
The results for all these lamps are shown in Fig.4.
It would
appear that these lamps are a very variable product; we
tested such a small sample that no other conclusions can
be made at this time.
The
Beam Characteristics
Spread
charts were constructed for one of the new 100watt Powersun
lamps with the higher output (Fig. 5a) and the 160watt Powersun
(Fig. 5b).
The
shape of the beams for these true flood lamps are very distinctive.
Like the beam of a fluorescent lamp, the UVB light radiates
fairly evenly from the lamp face in all directions forming
a UVB gradient in a spheroidal shape. Levels of UVB of 20uW/cm²,
for example, are maintained at the surface of this flattened
“sphere” for just under one and a half feet below, and just
over one foot to each side of the lamp.
These
flood lamps therefore supply a diffuse “glow” with a fairly
uniform UVB gradient, over a relatively large area, resembling
natural UVB “in the shade” on a sunny day.
Fig.6
shows a young iguana in his basking spot under the Zoo Med
Powersun 100watt lamp, using the spread chart to visualise
the UVB gradient.
Because
this lamp produces heat as well as UV light, it is vital
to check basking temperatures when positioning the lamp.
Here, the iguana is basking about 12” from his lamp, which
is the manufacturer’s recommended minimum distance. In this
particular vivarium, the lamp produces the correct amount
of heat, and what at least one author recommends as an adequate
level of UVB for an iguana, at this distance. This example
illustrates, however, the difficulty of using this type
of self ballasted lamp for reptiles with a higher UVB requirement.
The zones in which the UVB level rises to that approaching
sunlight are much too close to the lamp for safety; the
heat of the lamp could burn a reptile at such close range.
If higher
levels of UVB are required, or a beam which penetrates further
into the vivarium is needed, one of the Narrow
Flood MV lamps may be a suitable option.
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Several
years ago, another true flood lamp made by the Canadian
firm Westron Lighting Corporation was sold in the UK under
the brand name Active UV Heat Flood, distributed by Wild
Inside. A few of these are still in circulation, so we have
included this in our study for completeness. This is a large
lamp characterised by a thick brass ring at the base of
the neck. It has a smooth glass, semi-opaque face. It was
available in 100watt and 160watt self-ballasted versions.
(The lamps now being sold under the brand name Active UV
Heat Flood will be considered later, along with the “narrow
flood” lamps.)
Fig.8
shows the burn-in of the two lamps. One of the lamps showed
almost no decay over the test period; the other showed the
decay typical of "burning in", with a greater loss over
the first few hours. It started out with a higher output
but by the end of the test period, both lamps had a similar
output. This might suggest that the lamp that did not decay
had been used, and burned in, before we received it (although
it was stated to be brand new).
