Knoll Light Factory is not compatible with Photoshop CC 2015.5.
Mac OS X:
10.8.5, 10.9.5, 10.10
Mac Intel / 1GB of RAM / 30MB of Hard Drive Space
Windows 7 (64-bit), Windows 8 (64-bit), Windows 10 (64-bit)
Pentium 4 2.4 GHz or faster (or AMD equivalent) / 1 GB of RAM / 30MB of Hard Drive space
Adobe Photoshop CS5.5, CS6, CC, 2014, 2015
Since Knoll Light Factory for Photoshop is no longer updated/maintained, if it's running a host or operating system outside of these specifications, the program will not be guaranteed to work as it's technically in an unsupported environment.