To avoid being blinded by a bright screen at night, f.lux is free software that makes the color of your computer's display adapt to the time of day automatically: warm at night and like sunlight during the day.
1. Go to www.justgetflux.com and click on "Download Flux".
2. Open the installer in your Downloads folder then click the Flux icon.
3. Click "Open" and "Move to Applications Folder". Set your preferences (waking hours, location, color intensity, etc) and click "Done".