Summary

We have found that some of the plastic covers used over UVB tubes in Namiba Terra Replux Compact Light units (Namiba Terra GmbH - www.namibaterra.de) block over 99% of the UVB and most of the UVA. When one of these covers is placed over the tube it is instantly rendered useless as a source of UVA or UVB.

Introduction

Recently, we were asked to test a new European product which a British distributor was considering introducing to the UK market: a UVB fluorescent tube in a compact lamp unit supplied with a translucent plastic cover.

The lamps sent for testing were two brand new Namiba Terra Replux Fluorescent Tubes, size 15watt, length 18”, and two brand new Namiba Terra Replux Compact Lights, each of which consists of a metal frame enclosing a ballast and fittings for the 18” tube, plus a removable plastic translucent clip-on cover.

Fig. 1 shows one of the Compact Lights and one of the tubes, in their original packaging. Fig. 2 shows the fluorescent tube installed in the lamp unit, with the plastic cover which then clips over the front of the lamp.

We set up the tubes in the units, and took recordings of the UVB output of the lamps, with and without the plastic cover in place, using the Solarmeter Model 6.2 UVB manufactured by Solartech Inc. (www.solarmeter.com)

We then took a series of readings with the Ocean Optics Inc. USB 2000 Fibre Optic Spectrometer, (www.oceanoptics.com), again with and without the plastic cover in place.

Results.

UVB Meter Readings

UVB Output (uW/cm2) of two Namiba Terra Replux Fluorescent Tubes in Compact Light Units Distance from surface of tube (inches) Tube 1 with no cover Tube 1 with plastic cover Tube 2 with no cover Tube 2 with plastic cover 2" 122 1 118 1 4" 66 0 65 0 6" 43 0 43 0 8" 31 0 31 0 10" 22 0 22 0 12" 17 0 17 0 14" 14 0 14 0

The direct readings without the plastic cover show clearly that this is a normal type of UV-emitting fluorescent tube. The readings show how the output of a UVB fluorescent lamp decreases steadily as the distance increases from the lamp’s surface. These brand new lamps (after 30 minutes warm-up time) are both emitting 43 uW/cm² at 6ins and 17 uW/cm² at 12ins. This is an output similar to those we have seen with other UVB fluorescent tubes of this style. However, once the cover was put into place, the readings dropped to zero at all distances except 2” when a single microwatt per cm² was recorded. This plastic cover is an extremely effective UVB blocker. If one microwatt penetrates, when the unfiltered recording at 2” is 122uW/cm², this indicates a 99.2% block.

Spectrometer Readings

To make the spectrogram easier to understand, a representation of the electromagnetic spectrum, to the same scale, is shown underneath. The recording from the tube with no plastic cover is shown in blue; the recording with the plastic cover over the tube is in red.

Spectrogram 2 shows a recording made at a higher integration time – this increases the sensitivity of the spectrometer, enhancing the recording of just the UV wavelengths (290 – 400nm)

These spectrograms confirm the readings taken with the Solarmeter UVB meter. The fluorescent tube without the plastic cover has a spectrogram absolutely typical of UV-emitting tubes of this type. The mercury vapour emission spectrum produces intense “spikes” of light at distinct wavelengths (e.g., the peak at 365nm in the UVA range) and the mix of phosphors provide more evenly distributed light across the entire spectrum from UVB to infra-red, with the highest peak in the blue wavelengths at around 490nm. In the UV range, the lamp emits UV from about 295nm (in the UVB range) with a maximum at around 340nm (in the UVA range).

However, the change in the spectrum when the cover is applied is dramatic. The cover almost completely blocks transmission of all wavelengths below about 365nm; almost nothing at all is recorded in the UV region of the spectrum.

This plastic is effectively blocking UVB and all but the highest wavelength UVA, whilst allowing visible light to pass much more freely through.

Further tests were carried out. We recorded the output of the fluorescent tubes during a standard 105-hour burn-in period. We also conducted a transmission test using the spectrometer, comparing the UV transmission of the plastic cover with that of glass and of a sheet of UV-transmitting acrylic. The full report is available upon request.

The problem

The packaging on this product states, “Namiba compact lights can be used equipped with Replux fluorescent tubes… so that the UV radiation can arrive without reduction at the animal. The transparent plastic cover is made of an UV-permeable special plastic and is suitable therefore for the safe installation by UV tubes in the Terrarium”

Unfortunately, the transparent cover appears to be the absolute opposite to this – it blocks over 99% of the UVB.

When the cover is placed over the tube it is instantly rendered completely useless as a source of UVA or UVB.

Comments and recommendations

We contacted Namiba Terra GmbH immediately, and sent them a full report of our findings.

We have now had a reply from the President of the company, Paul Lutz Weynans.
He told us that they have now discovered that their manufacturer had changed the plastic cover and had not been using the UV permeable plastic which they had ordered.
He wrote that they had found that even the correct type of plastic reduced the output of UV by 30 - 40%, and so they were not satisfied with this type of cover.
He added that they are now working on a stainless steel "net" to replace the cover, and he offered to inform us when this was in production.

We asked whether the company were considering recalling the faulty product, or informing their distributors and customers of the problem with the plastic. However, we have not, as yet, received their reply. When we do, we will be pleased to publish details here on their behalf.

UPDATE: November 2006. We have heard nothing more. The product is still available from the Namiba Terra website. The illustrations in English no longer include a caption saying the acrylic allows UVB light through; however this claim is still made on the German listings.

We believe the implications are very serious.
Every reptile that is currently relying on these UVB lamps for its vitamin D3 synthesis, in whatever country these have been on sale, is now at risk of developing vitamin D deficiency and possibly metabolic bone disorder if the plastic cover has been fitted over the tube.
Metabolic bone disorder develops very slowly over several months; owners will not see any illness in an affected reptile for a very long period as the bone disease develops. However, once the bones are weakened and deformities appear, it may be too late to effect a complete cure.

Owners of these lamps must be informed of the situation.

All that is needed, to ensure that the reptiles are no longer at risk, is for the owners to remove the covers from their lamps at once.

This does, however, expose the ballast and its wiring; care must be taken to ensure that the reptile cannot gain access to this part of the lamp.

Provided that the lamp is sited suitably close to the reptile’s basking spot (we usually recommend a distance of 8 – 10 inches above the reptile’s back, for this type of fluorescent tube) the reptile will begin to obtain UVB light for vitamin D3 synthesis.