the main difference is that CELSIUS is a solar control type of glass - well worth considering in a conservatory
Pilkington Self Clean glass on the other hand is just a "normal" glass that has a self cleaning coating - mind you, Pilks have recently brought out For Pilkington Activ? Blue Conservatories - which I have no experience of, but seems a good idea
more info on all these products at:
http://www.conservatoriesonline.com/...ning_glass.htm (Pilkington Activ? self clean glass)
http://www.conservatoriesonline.com/...ning-glass.htm ( Pilkington Activ? Blue)
http://www.conservatoriesonline.com/...es_celsius.htm ( Celsius Performance Glass )