If this is common knowledge, I apologize, but I was unable to find any info about how to make low light vision work in roll 20 through my searches. After giving up on it, I finally found the solution and it is a very easy one. In the dynamic lighting tab, scroll to the bottom and open advanced and legacy settings for the token you want to give low light vision. Then set the light multiplier for that token to 200%. This way, only players controlling that token will have the modifier, anyone without low light vision will have the standard lighting vision. It works in addition to darkvision for any characters that happen to have both as well.