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The
surface temperature of a self-ballasted lamp is high, owing
to the combined heat output from the mercury vapour arc
tube and the incandescent filament. It is therefore important
that a reptile cannot come into contact with the lamp at
any time, as serious burns might result.
Mesh
guards
are often used to enclose hot bulbs; alternatively, bulbs
may be placed above screen tops
to prevent accidental contact. This experiment investigates
the drop in output that might be expected when placing a
mercury vapour lamp behind mesh of various types.
First,
the output of a 100watt Zoo Med Powersun
Flood Lamp was measured, in a ceramic holder affixed
to a wooden batten in a test room. The same lamp was then
tested behind a sheet of quarter-inch
twillweld wire mesh with wire thickness 1mm (such
as might be used for a protective screen) and inside two
commercially available mesh guards.
The
first guard was made from half-inch twillweld mesh with
1mm wire; the second was made from half-inch mesh using
a much thicker, white painted 2mm wire. (Fig. 1)
The
results are shown in Fig. 2 and are as expected: the thicker
the mesh, the more UVB is blocked.
At a
distance of 12”, for example, the wide spaced, thin-wired
mesh blocked about 14%, the
closer spaced mesh blocked 24%,
and the thickest white-painted mesh blocked 35%
of the UVB. The thickest mesh brought the UVB reading at
12" down from 37uW/cm² to 24uW/cm².
The
test was then repeated using a ReptileUV
Mega-Ray 100watt SB Narrow Flood lamp in place of
the Powersun lamp. The results are shown in Fig. 3.
The
output of this lamp is nearly seven times higher than the
other (compare the different scales on the graphs) but the
effect is very similar. At a distance of 12", the thin-wired
mesh blocked 15%, the closer
spaced mesh blocked 20%, and
the thickest white-painted mesh blocked 31%
of the UVB. The thickest mesh brought the UVB reading at
12" down from 252uW/cm² to 174uW/cm².
At close
distances, the readings for the two half-inch mesh guards
appear anomalously high. Perhaps this is due to the beam
from the narrow flood lamp being more coherent than the
true flood, and there is some type of interference effect
with the mesh. Or it could be that I just messed up the
readings. The ReptileUV Mega-Ray was too wide to physically
fit right inside the thick mesh guard and so I couldn't
get the meter closer than 8".
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