Answer
What causes glare and god-rays in VR headsets?
Scattered light. Fresnel grooves throw bright highlights into radial streaks, and any lens stack leaks a little light around high-contrast edges. Pancake optics cut it heavily but do not eliminate halos on very bright objects.
The mechanism
A perfect lens sends every ray where it belongs. Real lenses scatter a fraction of the light. In Fresnel optics the concentric grooves are discontinuities, and each one scatters — producing the radial streaks people call god-rays. In pancake optics, the polarising half-mirror leaks a small percentage of light on each pass, which shows up as a soft halo rather than streaks.
When you notice it
- White text or UI on a black background
- Night scenes with bright lamps, stars or muzzle flashes
- Letterboxed video with bright picture and black bars
Bright, evenly lit scenes hide it almost completely, which is why demo content rarely reveals the problem.
What reduces it
- Pancake optics over Fresnel
- Lowering display brightness in dark content
- Using a dark UI theme in virtual desktop apps
- Keeping the lenses clean — fingerprints and dust make scattering measurably worse
Note that god-rays are an optical property, not a software bug. No firmware update removes them.
Related: Pancake vs Fresnel - AR/VR headset optics guide
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- What is lens compression, and do long lenses really flatten faces?
- Is an f/1.2 lens worth it over f/1.8 for portraits?
- Why does bokeh look different between lenses at the same aperture?
- Pancake vs Fresnel lenses in VR headsets: what is the real difference?
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