Light olive oil has been more finely filtered to remove particulate. This results in a lighter flavor and a higher smoke point. This page tells alot about the various grades of olive oil:
Despite what the encyclopedia says, filtration is not a standard or acceptable processing step in producing olive oil. If there are any particulates (mostly droplets of water) in olive oil, these can be easily separated by settling. Furthermore, it's scientifically incorrect to say that the removal of such particulate would alter the smoking point of olive oil. This is so because olive oil plus particulates would be a mixture. By definition, the components of any mixture have the same properties as when they are pure. Thus it doesn't follow that the smoking point of olive oil would change because there may be some particulates in it. Another way to look at the claimed reason for the 'lightness' in olive oil is the following: 'Light' olive oil has become light because of filtration to remove particulates. Then non-light olive oil eg. extra virgin must contain such particulates. Is this really the case? Has anyone seen particulates in a bottle of non-light olive oil on supermarket shelves?
To sum it all up, there are no particulates in olive oil save for entrained droplets of water (technically the aqueous phase with which the olive oil is in contact prior to separation by settling or centrifugation) which will settle at the bottom over a period of a few weeks. Any further changes in the properties of olive oil can only be accomplished through chemical processing only.