Control of glare from sunlight – ‘openness factor’ of blinds

The ‘openness factor’ or ‘openness coefficient’ is the ratio between the area of openings and the total area of fabric. It is one of the factors in determining how much light will pass through the fabric of the blind.

For example, opaque Venetian blinds or close weave fabric blinds may have an openness factor of blind of 1% or less.

For further details, please refer to: BS EN 14501:2005 ‘Blinds and shutters — Thermal and visual comfort — Performance characteristics and classification’

06/10/2023 Updated to provide a relevant example to the definition.