ContrastAmplification [fact] v1.0.0

Light-on-dark text (negative polarity) needs ~10% higher contrast and slightly heavier weight than dark-on-light to feel equally legible, because halation around bright glyphs on dark backgrounds reduces effective edge sharpness.

Text rendered light-on-dark (negative polarity) requires roughly 10% higher luminance contrast and one weight step heavier than the same text dark-on-light to achieve perceptual parity, because of halation: bright glyphs on dark backgrounds bleed photons into adjacent dark pixels, softening edges and reducing effective contrast.

Confidence

strong

Applies To

• dark-mode token derivation (don't naive-invert)
• weight selection: bump body weight from 400 → 450/500 in dark themes
• OKLCH lightness tuning when mirroring light tokens to dark
• checking that AA-passing light tokens still pass when inverted

Quantitative

• Contrast Amplification Factor: ≈ 1.1× (10%)
• Weight Amplification: +50 weight units typical (e.g., 400 → 450)
• Halation Mechanism: subpixel rendering + LCD photon scatter on adjacent dark pixels

Counter Conditions

• OLED displays with true blacks reduce halation considerably — amplification factor closer to 1.0.
• Astigmatism users report inverse polarity preference — halation is more pronounced for them, but the discomfort flips relative to the median user.
• Variable-font weight axes let dark-mode amplification be a continuous tweak rather than a discrete weight step.

ContrastAmplification [fact] v1.0.0

Light-on-dark text (negative polarity) needs ~10% higher contrast and slightly heavier weight than dark-on-light to feel equally legible, because halation around bright glyphs on dark backgrounds reduces effective edge sharpness.

Text rendered light-on-dark (negative polarity) requires roughly 10% higher luminance contrast and one weight step heavier than the same text dark-on-light to achieve perceptual parity, because of halation: bright glyphs on dark backgrounds bleed photons into adjacent dark pixels, softening edges and reducing effective contrast.

Confidence

strong

Applies To

• dark-mode token derivation (don't naive-invert)
• weight selection: bump body weight from 400 → 450/500 in dark themes
• OKLCH lightness tuning when mirroring light tokens to dark
• checking that AA-passing light tokens still pass when inverted

Quantitative

• Contrast Amplification Factor: ≈ 1.1× (10%)
• Weight Amplification: +50 weight units typical (e.g., 400 → 450)
• Halation Mechanism: subpixel rendering + LCD photon scatter on adjacent dark pixels

Counter Conditions

• OLED displays with true blacks reduce halation considerably — amplification factor closer to 1.0.
• Astigmatism users report inverse polarity preference — halation is more pronounced for them, but the discomfort flips relative to the median user.
• Variable-font weight axes let dark-mode amplification be a continuous tweak rather than a discrete weight step.

Sources

Confidence

strong

Source

• Buchner & Baumgartner, 'Text–background polarity affects performance irrespective of ambient illumination', Ergonomics (2007)
• Piepenbrock et al., 'Positive Display Polarity Is Advantageous for Both Younger and Older Adults', Ergonomics (2014)
• IBM Carbon Design — Dark Theme white paper (contrast amplification rationale)

Applies To

• dark-mode token derivation (don't naive-invert)
• weight selection: bump body weight from 400 → 450/500 in dark themes
• OKLCH lightness tuning when mirroring light tokens to dark
• checking that AA-passing light tokens still pass when inverted

Quantitative

• Contrast Amplification Factor: ≈ 1.1× (10%)
• Weight Amplification: +50 weight units typical (e.g., 400 → 450)
• Halation Mechanism: subpixel rendering + LCD photon scatter on adjacent dark pixels

Counter Conditions

• OLED displays with true blacks reduce halation considerably — amplification factor closer to 1.0.
• Astigmatism users report inverse polarity preference — halation is more pronounced for them, but the discomfort flips relative to the median user.
• Variable-font weight axes let dark-mode amplification be a continuous tweak rather than a discrete weight step.