After trolling through many articles and spec's I can only find the difference being the actual naming of the two units.

I used the Philips TUV PL-S lamp as my test object, and it is found in both types of units...

I read articles on both types of UV units, and both summarised doing the same thing...

A UVC & UVS will:-

* Help protect fish against disease

* Cleans the aquarium/pond without using any chemicals

* Clarifies the water

* Controls moulds, bacteria and algae

* Kills Pathogens, parasites and germs

Disinfection of water using ultraviolet light (UV) is a proven technology. This safe and effective physical disinfectant is suitable for both large and small applications. Ultraviolet light, better known as UV, is one energy region of the electromagnetic spectrum. In this spectrum UV lies between visible light and X-rays. The shorter the wavelength the greater the energy produced, therefore UV has less energy than the X-ray region and more than visible light. The UV region is made up of four areas, Vacuum UV, UV C, UV B, and UV A. The UV A region is used for sun tanning lamps. UV B and UV C are the regions that contain the wavelengths effective for germicidal action. Wavelengths most effective in killing microbes lie below 300nm. Those most effective in producing ozone lie below 200nm. In most cases, we are interested in killing microbes, not in producing ozone, so we are concerned primarily with wavelengths between 200 and 300nm. Ultraviolet lamps and fluorescent lamps are similar in design. UV light is emitted as a result of current flow through the mercury vapor between the electrodes of the lamp. The most commonly use UV lamps produce the majority of their UV output at 253.7nm, a wavelength which is very close to the 260 - 265nm wavelengths which are most effective in killing microbes. The main differences between germicidal and fluorescent lamps are the germicidal lamp is constructed of UV transmitting quarts, whereas the fluorescent lamp has soft glass with an inside coating of phosphor which converts UV to visible light, the quartz tube transmits 93% of the lamps UV energy whereas the soft glass emits very little.
If there is someone who knows more technical information regarding this, please enlighten us all...