The chart shows the average daily insolation on a vertical wall facing in the given direction, for each month of the year. The amount of sunlight potential for the wall varies based on its direction, the time of day, and the time of year.

Tip

Move your device around to vary the direction it is facing and see how the light changes.

What does it tell me?

• How the amount and intensity of sunlight varies based on time of year
• How the direction the wall faces affects the potential sunlight received
• Gives an indication of how much sunlight may come through a window facing in the given direction

Note: the chart does not account for shade from structures or objects (e.g. buildings or trees) or cloud cover.

Insolation is a measure of the power of sunlight reaching a surface. It is usually given for a period of time, e.g. per hour, per day, per month.

Insolation for a wall indicates the sunlight potential based on the direction, or aspect, which the wall faces

The values may seem counterintuitive at first: for example, at mid-northern latitudes, a south-facing wall receives more mid-day insolation in December than in June. This is because the sun remains lower in the sky in winter, and so shines more directly on the wall than in summer, where the high angle of incidence around noon reduces the insolation received.