I am trying to figure out what these light patches of grass in my lawn are? and how to get rid of them? They started to appear after I installed an irrigation system and seem to be getting larger and spreading. I notice them the most in the areas that get a lot of shade? Is it Poa Trivialis?
The problem with identifying grasses is that many of them differ by very little details, and often we cut off the pieces that are the most helpful in distinguishing between them when mowing them short for the lawn. Your id process will be much easier if you can find a spot where those grasses have been allowed to grow to maturity and produce a flower head of some sort. Then dig a couple of specimens and wash off the soil so that you have root to tip samples available.
Then the wiki page description of the plant will begin to make some sense when it refers to small details like stolons and ligules. A magnifying glass will come in handy. Often you can eliminate some grasses from possibles quite quickly. It is probably much easier for readers to help if you can post back additional details that can help us to zoom in with you.
There are some Youtube videos available which I am sure you must have tried first. If these pointed out some features that your plant does not possess then that is also helpful information.
This looks very much like female doggie pee. In fertilized grass, that urine will kill, brown the grass. In unfertilized grass as in your second pic, that urine will green the grass.