Rooflights an alternative roof window to dormers. Rooflights follow the line of the roof and are usually a more acceptable proposal to planning authorities. Rooflights are available in a variety of sizes, and shapes these can be vented fixed or open-able

Polycarbonate and clear glass glazing may provide direct daylight lighting. Direct light passes through rooflight glazing without any disruption or interference and enters the building as a straight beam.

Direct light

  • Gives strong light in the area of the beam but less general light in the surrounding areas.
  • Produces shadows and glare on sunny days.
  • Is ideal for environments where the designer wants to create a natural environment and allow the sky to be viewed.
  • Gives uninterrupted external vision.
  • Diffused light is when the light passing through rooflight glazing is diffused (scattered) by the rooflight material. Polycarbonate, Nanogel® and some patterned and opal-tinted glass materials diffuse light.

Diffused light

  • More evenly distributes light into the building.
  • Is useful for creating ambient light over a larger area with minimal shadows.
  • Is commonly used for industrial, commercial and sporting facilities.
  • Provides privacy.

Based on records, it is assumed that average outdoor illumination is 5,000 lux for 85% of the normal working day which represents a ‘dull’ day by most standards. By the same standards, a sunny day is assumed to be 100,000 lux, which is taken as a maximum level of illuminance for design purposes.

Practical Examples of Daylight Factors

  • Daylight Factor
  • less than 2%
  • Room looks gloomy
  • Often needs full artificial lighting during the day
  • Decor is dominated by the appearance of artificial lights
  • Daylight Factor between 2 – 5%

The optimum range of daylighting for efficient energy use

  • Room appears to be predominantly lit by daylight
  • Artificial lighting is required away from rooflights and on dull days
  • Daylight Factor greater than 5%
  • Room appears to be strongly lit by daylight
  • Artificial lighting rarely required during the day
  • Potential solar gain is a consideration and therefore careful specification is required