The Hole Story:
The Mouse Model of Cancer ctd.
We know in simple terms that ozone depletion is occurring and will cause more skin cancers but scientific research is a quest for more precise knowledge. Given our understanding of the effects of UV on skin it the relative lack of knowledge regarding ozone depletion and its effects which is most disturbing. It is to this end that Greenoak has been involved in work to devise a new type of light source which will simulate the total sunlight spectrum. It has been built in consultation with the CSIRO Division of Applied Physics.
The device has taken 10 years to develop and has been Greenoak's particular goal since he first started working in this field. It always seemed to me that to get any meaningful result, whether it be for the effectiveness of a particular sunscreen or looking at skin cancer or the biological affect of the skin, we have to use sunlight. But you can't just use natural sunlight because you can't control it. It varies from day to day and hour to hour. The reason a solar simulator hasn’t been made before now is because sunlight is so complicated to simulate, he says.
To date most of the work on skin cancer has only used UV light. In the past two methods have been generally used. The first uses fluorescent tubing which will emit UV light. These tubes are usually mercury arc lamps with a phosphor coating which converts the different wavelengths of UV light to a more continuous spectrum. The other way is to use a xenon arc lamp, which is a much more cumbersome light source. This is because it is very fragile and produces toxic ozone. But to date it has been the closest approximation to sunlight when used with various filters.
With the new solar simulator, they have taken advantage of the most recent technology in fluorescent tubes and phospor coatings and put together an array of different kinds of light sources. There are two reasons for this extended array. Firstly so that each part of the sunlight spectrum can be independently varied in order to answer a variety of questions about the different contributions that visible light, infrared and UVA make to skin damage. The other reason is that it is easier for maintenance and keeping up with new technologies.
The instrument has also been designed to simulate the role of the ozone layer in filtering UV light. Up to now cellulose triacetate filters have been used for this purpose which have a much better spectral cutoff than glass. But unfortunately these filters gradually break down under the light and they are very expensive to replace. This material has also been in short supply recently because it is used in graphics and has become very popular, particularly with cartoonists. The method being developed now as a means of simulating atmospheric ozone involves the use of ozone gas together with the solar simulator.
Another area for the simulator to explore will be effects like cloud cover. Many people may have noticed that when cloud is coming over, the light in the sky often seems to become more intense. When a cloud approaches the sun there is an immediate increase in UV light exposure because there is added reflection due to the light being reflected off the clouds. It isn't known what effect that might have on biological systems but the new instrument will be able to simulate this condition and assist researchers to find out.
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