Rooflight Glazing Light Transmission Qualities

The light transmission (LT) qualities of complete rooflights vary according to the glazing configuration and the LT of materials used. As it passes through each layer, the light transmitted is reduced cumulatively, as shown in the example.

The four charts show the percentage reduction in available light within a building using various rooflight glazing materials and configurations, as follows. Where appropriate, intermediate and inner skins are assumed to be clear polycarbonate.

Light Transmission

Solid Polycarbonate

Single skin—only recommended for unheated areas.
Double skin—non-preferred as it does not meet current Part L requirements.
Triple skin—meets Part L and gives improved sound insulation.
Quadruple skin—further improvement of performance characteristics.

There are substantial differences between various types of polycarbonate with ‘Opal’ giving only half the LT of clear, while the popular ‘Diffused’ transmits just 1% less than clear with a very good light spread.

Structured Multi-Wall Sheet

Available in three thicknesses to suit thermal and other requirements.

Nanogel® Sheet

The latest advanced glazing technology with excellent thermal, light diffusion and acoustic performance characteristics.