On what computer operating system is your Premiere Elements 11 running?
What is the source of the Light Leaks Effects, and what does not manufacturer give for the requirements and download installation
There are times when Premiere Pro 3rd party effects can be used in Premiere Elements, sometimes not.
I did so Googling to see what I could find in the way of "Light Leaks" effects,
I came across one web site offering free ones that were described as "1080p HD clips".
A "1080p HD clip" should import into Premiere Elements, provided the video and audio compressions of the file plus
its file extension are supported by Premiere Elements. If this find is characteristic of what is out there with regard to
these "Light Leaks" effects, then what we need to go after are the properties of these "1080p HD clips". They do not
appear to be plug-ins, rather files imported (hopefully) into the project with the project's Add Media/Files and Folders.