ANGULAR SELECTIVE SKYLIGHT

BENEFITS : More natural light during the early morning, late afternoon and winter when the sun angle is low. Less heat in the middle of the day in summer when the sun angle is high.

HOW IT WORKS: Laser cut panel contains hundreds of tiny mirrors that powerfully redirect sunlight. A pyramid of four laser cut panels is installed inside the clear dome of a conventional pyramid skylight to form an angular selective skylight. The effect on sunlight is shown below:

A is a conventional skylight. It has a clear dome (green) in the roof and a diffuser panel (light blue) at the ceiling level. Low angle sunlight does not penetrate down to the ceiling diffuser and natural lighting is poor.

B is an angular selective skylight. Now, much of the low angle sunlight is redirected by the laser cut panels onto the diffuser providing natural light to the room.

C shows how a conventional skylight can admit too much sunlight in the middle of the day in summer resulting in overheating of the room

D shows how the angular selective skylight rejects the high angle summer sun and keeps the room cooler in summer.

DESIGNING WITH ANGULAR SELECTIVE SKYLIGHTS :

Several parameters can be varied to allow the architect to design for specific performance. A useful parameter is sunlight or radiant heat transmittance versus time of day. In sub tropical climates it is desirable to reduce radiant heat gain in the middle of the day in summer. This makes skylights far more useful in occupied spaces such as offices and schoolrooms.

As an illustration the angle of the pyramid is varied from 45 o to 55 o for skylights specified for Sydney . Shading factor SF is the ratio of the radiant input of the angular selective skylight to the radiant input of conventional clear skylight. Thus if the angular selective admits 25% more than the clear skylight the shading factor is 1.25 or if the angular selective admits 25% less than the clear skylight the shading factor is 0.75. The results in the graphs below are for a clear sky conditions and take into account both direct sunlight and diffuse sky. The first graph is for mid summer and the second graph for mid winter. Similar graphs can be calculated for any location and any time of year.

For further information or technical assistance on angular selective skylights contact Skydome via the `Contact Us' links or phone during business hours.