Sunlight basics

Direction is only the beginning

“South-facing is sunny” is a Northern Hemisphere rule of thumb, not a universal result. Latitude, season, window height and nearby obstructions can reverse the practical outcome. Near the tropics, the midday sun can pass on different sides of a building during the year.

Azimuth tells you where to look

Solar azimuth is the compass bearing toward the sun. SunCarta measures it clockwise from true north: 90° is east, 180° south and 270° west. Compare it with the direction a window, facade or camera faces.

A difference below 90° places the sun broadly in front of that plane. A difference near 90° creates side light. A larger difference places the sun behind it.

Altitude controls shadow length

Solar altitude is the angle above the horizon. When the angle is low, a modest wall can cast a long shadow. As altitude rises, the same wall’s shadow contracts. That is why winter and late-afternoon tests matter even when a place looks clear at summer noon.

Direct sun is not the same as daylight

Direct sun is a beam with a clear geometric path. Daylight also includes the bright sky and light reflected by walls, ground and neighboring buildings. A room can have zero direct sun and still be comfortable and bright; conversely, a short direct beam can cause glare without illuminating the whole room.

Use representative dates

For a first comparison, test a date near each solstice and equinox. Then test the actual season that matters: the growing months for a garden, the listing period for an apartment, or the scheduled date and hours for an event.

• Use the same dates and assumptions when comparing alternatives.
• Measure the obstacle most likely to change the decision.
• Test plausible low and high dimensions when a height is uncertain.
• Visit the place at a relevant time before a consequential purchase when possible.