Screen Brightness Calculator

Screen brightness optimization reduces eye strain, improves visual comfort, and can extend battery life on portable devices. The key principle is matching your screen brightness to the ambient lighting conditions.

The matching rule: Your screen should be approximately the same brightness as your surroundings. If the screen is much brighter than the room, your pupils constrict. If it is much dimmer, your pupils dilate. Both cause eye fatigue over time.

Recommended brightness by environment:

Additional display settings for comfort:

• Color temperature: 5,500–6,500K in the morning, 5,000–6,000K through the afternoon, 3,500–4,500K in the evening and 2,700–3,500K after 10 PM
• Blue light filter: Enable in the evening to support natural sleep patterns
• Contrast: Keep at 60–80% for most conditions
• Text size: If you squint, increase font size rather than brightness

When to use this calculator:

• Setting up a new monitor or workspace
• Reducing eye strain during long work sessions
• Optimizing settings for different times of day
• Extending laptop or tablet battery life

Practical example: In a typical office with 400 lux ambient light, your monitor should be set to about 150–200 nits (roughly 50% brightness on most displays). At night in a dark room, dropping to 20–40 nits (15%) prevents eye strain.

The 20-20-20 rule: Every 20 minutes, look at something 20 feet (6 meters) away for 20 seconds. This relaxes the focusing muscles in your eyes and reduces digital eye strain, regardless of brightness settings.

Tips:

• Matte screens cause less glare than glossy screens.
• Position your monitor to avoid window reflections on the screen.
• The top of your screen should be at or slightly below eye level.
• Blinking rate drops by about half when you stare at a screen, so blink deliberately now and then.
• Dark mode (light text on dark background) can reduce eye strain in dim environments.

About the battery figure. For a laptop, tablet or phone this page estimates what dropping the brightness buys you. The backlight is roughly 40% of what a portable device draws while you are reading rather than compiling, so cutting brightness in half saves around a fifth of total power. That is the ratio behind the number, and it is a rough one: an OLED phone showing a dark page saves far more, and a laptop with the fans running saves far less.