The easiest way of doing this in Windows is to hit the Windows button, usually in the lower left corner of the screen, and type:
This will open Network Connections window:
Highlight the item 'Internet Protocol Version 4 (TCP/IPv4)' ( step 2.) and click on 'Properties' (step 3.).
If you already have numbers entered at the field 'IP address' or 'Subnet mask' you probably want to write these down to be able to restore the settings once you are done with this guide.
Enter the settings displayed in the image above and click 'OK', then 'OK' (or 'Close' depending on Windows version).
Now, your computer is ready to connect with the ethernet cable directly to your light.