Download of Nightlight 1.3 for Mac was available from the developer's website when we last checked. We cannot confirm if there is a free download of this app available. The actual developer of this free Mac application is David Wu. We recommend checking the downloaded files with any free antivirus. The application belongs to Internet & Network Tools.
From the developer:
Nightlight is a Safari extension that darkens web pages for a more pleasant browsing experience at night. You can configure the application to turn on automatically at a set time or at sunset. You can enable Nightlight by checking the box in Safari › Preferences › Extensions.
You may want to check out more software for Mac, such as NightLights Desktop, which might be similar to Nightlight.