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
