LightBulb is a f.lux-like application which smoothly adjusts screen gamma to make colours seem warmer at night, reducing eye strain and making your PC more comfortable to use.

Install the program and it goes to work automatically, detecting your location, figuring out the sunrise and sunset time and updating your display colour temperature accordingly.

Right-clicking the LightBulb icon in your system tray and selecting "Configure" displays some useful options and tools. To get started, click the "Preview 24-hour cycle" icon and watch as the program shows you how your display colour temperature will change over time. If that's too much, or too little, use the sliders to adjust the daytime and night time colour temperatures and hit Preview to see the change.

Elsewhere, a "Gamma Polling" option refreshes the current gamma settings every five seconds, handy if another application tries to change them.

If you'd prefer other applications to be able to take control, Gamma Polling can be disabled, and it's also possible to disable the effect when a full screen application is in the foreground.

If this causes problems at any time - maybe you're editing graphics and need to see colours as they really are - the effect can be disabled in a click or two, either entirely or for a defined period of time. Alternatively,  close the program at any time and your screen will immediately return to normal.

v1.6.3.5 (Changelog):

Fixed users being able to use Enter, Space or Tab as a hotkey without modifiers. (#47)
Implement periodical autosaving for settings instead of relying on saving on exit. (#62)
Fixed Windows 8 start menu getting recognized as a full screen application. (#46)
Make early transitions (night to day) start at sunrise instead of ending at sunrise.

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LightBulb seems to be finding your location by using your external IP address, which might be a problem if you're using a VPN. But otherwise it's a likeable and configurable tool which really can make your monitor more comfortable to read.