From my knowledge, light has been removed as a reason for objecting in relation to residential applications (ie neighbour extension) etc. There is no set list of grounds on which you can object, however, there are specific areas you should cover such such as those already outlined above (the zoning of the area, the zoning of the lands proposed for development, validity of application, purpose of proposal etc). I objected to something last year and got some advice from a planning consultant as to how best to object. I was advised your objection should be well written and presented, must include your full name, address and telephone number and must include valid reasons for objection and the specifics of the proposal that you are objecting to. Buzz words to use are those like 'adverse impact on residential property', potential environmental concerns, detrimential impact on the value / use / enjoyment of your property, and danger to public safety (site lines too tight etc), 'blending' in with existing properties, appropriateness of proposal etc.
Have a look on Dublin City Councils website for details of how to object, if you do decide to go ahead, the last thing you need to do is subject an invalid objection and miss the cut off date. Best of luck.