And to further rubberstamp the choice Peter, @gardatraffic (twitter) are actively testing with light meters --> http://rsa.ie/RSA/Your-Vehicle/Your-Vehicle-/NCT/Modified-Vehicles-/

Window Tinting

Excessively tinted windscreens or front side windows present a significant safety hazard for vehicle drivers and their occupants. Visibility is greatly reduced, particularly for night time driving and at times of low light. There are also enforcement issues for An Garda Síochána in regard to driver recognition, the detection of driving offences e.g. holding a mobile phone while driving, and other criminal activity.

If the NCT vehicle inspector deems that the windscreen or front side windows are excessively tinted the level of light transmission of the window will be tested. The glass in the windscreen and front side windows will be required to have a light transmission level of not less than 65% in order to pass the NCT test. Tinting of these windows must not be greater than 35%.Unfortunately the National Car Testing Regulations do not allow for any exemptions in this regard.

Tint films tend to be quite easily removed and replaceable with a compliant film which would block UVA light and meet the requirement of not less than 65% light transmission. There is no limit on the tint level in the rear window and rear side windows.