Consulting Service

To guarantee that your project achieves the desired level of lighting, our team of experts are on hand to assist architects and specifiers through the Xtralite Daylight Consulting Service.

Given that few rooms are uniform in shape, the standard methods of calculating daylight cannot always be relied on to ensure optimum positioning of rooflights and windows. As such, Xtralite offers a free consulting service that combines specialist expertise with advanced computer modelling to assist designers in achieving the maximum benefit of rooflights in their architectural proposition.

To illustrate, diagram 1A shows a standard sized room with windows along two sides. When analysed using Xtralite’s modelling system, it can be seen in diagram 1B that the Daylight Factor is very high in proximity to the windows, and significantly lower in the rest of the room.

Diagram 2A shows the same size room, but this time featuring a combination of several smaller windows and rooflights. Using the same modelling system, we see that the daylight is much more evenly distributed - as shown in diagram 2B.

If we compare the two layouts, the window and rooflight configuration in the second example not only produces a higher average Daylight Factor, but utilises a smaller glazed area too.

To find out more about Xtralite’s free consultancy services, contact our sales team today.


The design and materials of rooflights influence their light transmission (LT) qualities. For example, polycarbonate systems range from 79% for a double skin clear product and 77% for a double skin diffusing product. Similar products in bronze or opal can offer around 45%.

If we use the same formula shown in the diagram and consider a rooflight with a triple skin and a clear polycarbonate intermediate and an inner diffuser, the overall amount of light transmitted into the space would be 69%.

Alternatively, if the outer skin offers a light transmission of 70% and the inner skin 75%, then the overall level of light would be reduced to 52% - effectively losing over 30% of the available light into the building.


The materials specified in rooflights play an important role in determining the type, and amount, of light that enters a building. If direct light and diffused light materials have the same light transmission rating, they will let in equal amounts of light - it will simply be distributed in a different manner.


Direct light passes straight through rooflight glazing without disruption or interference, entering the building as a straight beam. Polycarbonate and clear glass materials provide direct light.

  • Direct light provides strong light around the beam, but with less scatter into the surrounding area.
  • Direct light produces shadows and glare on sunny days.
  • Direct light is ideal for environments where the designer wants to create a natural feel with the sky on view.
  • Direct light materials provide unobscured external views


When passing through rooflight glazing, diffused light is scattered by the materials used in the rooflight. Polycarbonate and some patterned and opal tinted glass materials diffuse light in this way.

  • Diffused light distributes light more evenly.
  • Diffused light is particularly useful for creating ambient light with minimal shadows.
  • Diffused light is commonly used in industrial, commercial and sporting facilities.
  • Diffused light materials provide greater privacy.
1A & 1B



Room dimensions:
20 m x 15 m x 3 m
18 m x 1.2 m and 13 m x 1.2 m
Total glazed area:
37.2 m²
Minimum daylight factor:
Average daylight factor:
Maximum daylight factor:

2A & 2B



Room dimensions:
20 m x 15 m x 3 m
5 windows, each being 2 m x 1.2 m
Total window area:
12 m²
12 rooflights, each being 1.2 m x 1.2 m
Total rooflight area:
17.28 m²
Total glazed area:
29.28 m²

Minimum daylight factor:

Average daylight factor:
Maximum daylight factor: