2.3 Some Basic Principles Of Daylighting?
No daylighting rule can be universally applied, but the following guidelines will
be helpful in most situations:
- Provide a wide diffusion of daylighting into a space through the
use of glazing and shading.
- Direct sunlight is usually reserved for circulation spaces
- Bring daylight in from as high as possible.
- Light colored surfaces will aid in both the amount and the distribution
- Use blinds and louvers to properly control daylight.
- Design daylight for the task. If the occupants require bright light,
darkness, or a highly controllable lighting environment, tailor the design solutions
to meet their needs.
- Long, narrow footprints, running East-West, are typically preferred.
- Use external building features for shading.
In the following example, direct sunlight from a large skylight in the center of
the room poses a problem. The illumination in the beam may be as high as 50,000
lux while the inter-reflected component on the wall may be less than 500 lux, giving
us a luminance ratio far in excess of the recommended 10:1.The excessive brightness
can cause problems with visual clarity and visual and thermal comfort.
What if we had achieved the same effect using electric lights instead? Typically
one needs to apply the rules of electric lights when designing daylighting systems:
- Control glare
- Balance surface luminances
- Create interest in the space
- Provide good color rendering
Excessive daylight Source: Benya Lighting Design
St. Georges Hall
Sometimes significant direct sunlight is desired. The Bank of Hong Kong/Shanghai
wanted to attract customers into the building by providing intense sunlight patterns
at the floor of a core atrium that was 12 stories high. The photos show how the
bank guided sunlight to the floor of the atrium while using an automated blind system
to shade direct sunlight from other parts of the space.
Over 400 mirrors were hung on the exterior of the building to track and redirect
sunlight into the bank of inner mirrors.
The light passes along the 11th and 12th floors towards the interior mirrors which
hung over the atrium.
The interior mirrors spread the light over the glass 'underbelly' which served as
the lobby ceiling.
Daylighting is like most visually based processes, beauty is in the eye of the beholder.
Some will find this daylight school classroom visually interesting. Others will
feel that this system provides too great a difference in luminances on the wall
making it difficult for students to see the writing on the board.
Daylighting for a classroom Source: Benya Lighting Design