Performance metrics & physics
Diffuse vs Direct Radiation
Solar radiation reaches the ground as direct (line-of-sight to the sun) and diffuse (scattered through clouds and atmosphere); window film rejects both components proportionally.
Direct radiation is the bright sunlight you can trace back to the sun. Diffuse radiation is the scattered light that makes the sky bright and lights up shaded areas.
In Singapore's often-hazy or partly-cloudy conditions, diffuse radiation can be 40–60% of total solar input. Even when the sun isn't directly visible, the cabin still receives substantial heat.
Window film rejects both components — there's no "only works in direct sun" effect. The solar heat rejection spec applies to the full solar spectrum regardless of how it reaches the glass.