Test Information
The Brightness & HDR test evaluates your display’s peak luminance and Average Picture Level (APL) handling. Modern displays, especially OLEDs and Mini-LEDs, manage their light output dynamically based on how much of the screen is white.
🔲 Window Size (1–100%): Use the slider to adjust the size of the white window. A 100% (FULL) window tests full-field sustained brightness, while smaller windows (1%, 5%, 10%) test “peak luminance.”
📐 Presets (1%, 5%, 10%, 25%, 50%, FULL): These are the standard industry calibration sizes used for monitor reviews and HDR certifications.
⬅️➡️ Navigation: Click the background or use Arrow Keys to cycle through window size presets.
🔋 ABL/ASL Behavior: On OLED screens, you will notice the screen dims significantly as the white window grows larger. This is the Automatic Brightness Limiter (ABL), which prevents overheating and protects the power supply.
☀️ Peak Brightness: Most HDR displays achieve their highest nit values at the 1% or 10% window sizes. Watch for any flickering or instability in the backlight as you change sizes.
✨ Haloing (LCD/Mini-LED): On displays with zone dimming, look for a “glow” around the white box against the absolute black background.
A high-quality HDR display should maintain consistent window brightness up to at least 10% and have a smooth, predictable dimming curve as APL increases. If your screen has “aggressive ABL,” the brightness will drop sharply the moment you move past a 10% window, which can be distracting during productivity work or gaming.
Online monitor brightness tester, HDR peak luminance tool, APL behavior check, OLED ABL diagnostic, nit measurement helper.