ARC 332 Environmental Controls I: Solar Geometry, Daylight, and Shading Techniques

Solar declination

The angle between the Sun's rays and Earth's equatorial plane.

Cause of solar declination

Earth's rotation axis is about 23.5 degrees off perpendicular to the Sun/Earth plane.

Northern Hemisphere, June 21

Higher solar paths and longer days.

Northern Hemisphere, December 21

Lower solar paths and shorter days.

Southern Hemisphere seasonal pattern

Around June 21, solar paths are lower and days are shorter; around December 21, solar paths are higher and days are longer.

Solar altitude

The vertical angle of the Sun above the horizon.

Solar azimuth

The horizontal direction of the Sun.

Azimuth conventions

In maps/GIS/navigation, North is 0 degrees and East is 90 degrees.

VSA

Vertical Shadow Angle is used primarily to design horizontal overhangs.

HSA

Horizontal Shadow Angle is used primarily to design vertical fins.

Overhang depth formula

OD = WH / tan(VSA) where WH = window height.

Fin depth formula

FD = WW / tan(HSA) where WW = window width.

Solar exposure for West facades

Can receive direct sunlight from the early afternoon toward sunset.

Light speed

Light travels faster than sound.

Light spectrum

Shows how radiant energy is distributed across wavelengths.

Selective absorption

An object absorbs some component colors and reflects or transmits the remaining light, changing its composition.

CCT

Correlated color temperature describes apparent warmth or coolness.

Typical CCT values

About 2800 K is warm, about 4000 K is neutral/cool white, and about 7000 K is very cool/bluish.

CRI

Color rendering index describes how well a source renders object colors compared with a standard reference.

Luminous flux

How much light the source produces; measured in lumens.

Luminous intensity

How much light the source emits in a given direction; measured in candela.

Illuminance

How much light reaches a surface; measured in lux or footcandles.

Luminance

How bright a surface appears to the eye; commonly measured in cd/m2.

Inverse-square law

Illuminance E2 = E1 x (d1 / d2)^2; doubling distance reduces illuminance to one-fourth.

Light adaptation

Moving from dark to bright generally happens faster.

Dark adaptation

Moving from bright to dark generally takes longer.

Window-to-wall ratio (WWR)

WWR = (window area / gross wall area) x 100.

2.5H rule

Useful daylight reaches about 2.5 times the vertical distance between the window head and task plane.

Daylight factor (DF)

DF = (interior illuminance / exterior illuminance) x 100.

Glare

Interference with visual perception from an uncomfortably bright source or reflection.

Veiling reflection

A reflection that reduces contrast on a visual task.