The Effect of Mesh and Screen

upon the output of

UVB Fluorescent Tubes

Mesh and Screen in the Vivarium

Anything that is placed between the lamp and the reptile will absorb a percentage of the UVB.

Ordinary glass will absorb 99-100% of the UVB; most plastics will absorb almost all. It is therefore very important that there is no plastic or glass between the bare tube and the reptile. Some fluorescent tube fixtures are sold with transparent shields; these must be removed, as UVB will not pass through.

Panels of wire mesh or fly screen are often used as lids or ventilation panels for vivaria, and enclosures completely constructed with nylon mesh are increasing in popularity. It is quite common for fluorescent tubes to be placed outside of the vivarium, with the mesh or screen between the tube and the reptile. Wire mesh or fly screen significantly reduce transmission, mainly by physically blocking the passage of the UV light.

For species requiring lower levels of UV light, the reduction in UVB caused by mesh may be useful. Species needing high UVB, though, will need to bask closer to a UVB source if there is mesh between the lamp and the reptile. Use of a reflector behind the tube may compensate for the reduction, however.

To investigate the loss of UV light which occurs when mesh is placed in front of a fluorescent tube, we measured the transmission of UVB light from several brands of fluorescent tube with various combinations of mesh and reflectors.

The Mesh Test Experiments

Method

Two types of mesh were used in the experiments:

• 5mm galvanised mesh
• Black fly screen mesh

Three types of reflectors were used:

• A commercially produced aluminium reflector
• A home-made reflector made of several layers of flat aluminium foil
• A home-made reflector, made in the same way, bent into a curve to fit behind the tube

A full set of tests using the mesh and reflectors was conducted on each of four 24" fluorescent tubes, one each of the following:

• Zoo Med Reptisun 5.0
• Arcadia 5.0 D3 Reptile
• ExoTerra Repti Glo 8.0
• ExoTerra Repti Glo 5.0

For each set of tests, the tube on test was set up at the back of an empty vivarium, and allowed to warm up for a minimum of 10 minutes, until a constant output was reached.

Series of readings were then taken with the tube alone, or with one of the two types of mesh placed directly in front of it, with or without one of the reflectors. The different combinations for each series are given in the Key (below)

Readings were taken at 2-inch intervals, at distances of 2 - 16 inches from the surface of the tube, for each series.

The results for the set of tests conducted with a Zoo Med Reptisun 5.0 tube as the source of UVB, are given below. The results using the other three tubes, despite their differing output, were directly comparable in terms of the percentage reduction of effective output caused by the mesh, and the percentage increase in effective output produced by the reflectors.

Results

Key to symbols in Layout Diagrams
UV tube		UV tube + reflector
UVB meter		UV tube + flat aluminium foil
5mm mesh		UV tube + curved aluminium foil
fly screen

Key to Graph 1: The Effect of Reflectors and Mesh upon the Output of a Zoo Med Reptisun 5.0 UVB Fluorescent Tube (length 24", diameter 1.0")
Test series	Layout	Description	Items used
1		UV tube without reflector. No mesh in-between light and meter
2		UV tube without reflector. 5mm galvanised mesh between light and meter
3		UV tube without reflector. Aluminium black fly screen between light and meter
4		UV tube with reflector. No mesh between light and meter
5		UV tube with reflector. 5mm galvanised mesh between light and meter.
6		UV tube with reflector. Aluminium black fly screen between light and meter
7		UV tube with flat aluminium foil above the light. No mesh between light and meter
8		UV tube with curved aluminium foil above the light.No mesh between light and meter

Discussion

If 5mm zinc plated mesh is placed in front of the tube, a 15-20% reduction in output is seen. (Compare Series 1 with Series 2).

25-35% losses occur with fly screen of the type often used for chameleon vivaria (Series 3).

To obtain the same UVB exposure, the reptile will need to be considerably closer to the tube if it is behind either type of barrier. Conversely, for species requiring low UVB, the mesh may be used to deliberately reduce the levels received.

However, these losses may be compensated for, by affixing a reflector behind the tube. This, as we have seen, typically increases the effective output by up to 100% and so even placing flyscreen in front will not reduce the UVB level to below that of a tube with no reflector fitted. (Compare Series 6 with Series 1).

The greatest effective increase in output is seen with the commercially available reflector (Series 4). However, a home-made reflector, simply made by folding layers of ordinary aluminium foil proved very effective (Series 8).

When a flat sheet of aluminium foil was placed behind the light, little increase in output was recorded (Series 7). However, separate tests have shown that this does slightly increase the overall amount of UV available in the vivarium. The light from behind the tube, which is reflected back into the vivarium, is directed into the vivarium at an angle, and hence is not recorded by the meter placed directly in line with the tube.

The full details of this set of experiments form part of an article on Lighting for Chameleons by Rob Lane as published on www.UKChameleons.co.uk.
Direct link to article (opens in new window): http://www.martinsreptiles.co.uk/ukchams/uvlightingresearch.htm
Download full set of results for these tests: (pdf file - 165KB):
http://www.martinsreptiles.co.uk/ukchams/intro_uvlighting_tests.pdf

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