Some customers have reported that the light intensity sometimes spikes on days when there is a mixture of sun and clouds. They expect the light to be at maximum intensity on a clear and sunny day and are surprised to see higher levels of solar intensity on days when there are clouds in the sky.
Why does this happen?
The short periods of high intensity occur when clouds do not completely cover the Sun's disk. When this happens, not only do the direct rays from the sun still reach the Earth's surface without obstruction but the portion of the light that goes through the clouds is refracted, scattering the light. The combination of the direct sunlight and the refracted sunlight can cause the light intensity to increase. You can actually see this phenomenon occurring when you look at clouds. It shows up as a silver lining around the edge of the cloud.
What is the result?
When a cloud covers the sun's disk, the intensity decreases rapidly. But when the sun starts to go behind the clouds and when the sun reappears from behind the clouds the intensity becomes very high. Usually this is only for a few minutes but it could be longer if the side of the cloud continues to partially cover the sun as it moves.
What can I do about it?
It is possible in the Compass to slow down the rate of change of the light intensity. The maximum sunlight intensity change per minute is found in the Configuration page of the zone with the physical weather station. If this is set at 0, any changes in light intensity are immediately registered in the system. If you put a value other than 0 in this field, the light intensity will not change as rapidly. For instance, if you put in a value of 20 W/m2 and the light intensity changes by 100 W/m2, it will take 5 minutes for the change in intensity to be fully registered. The Advances Status page will always show what the light intensity is without this damping effect.