daylighting

Question 1

Explain the concept of daylighting

Answer 1

It means designing the lighting system to be controlled in such a way that the energy used in lighting is reduced when daylight is available.

Question 2

Explain the concept of daylight factor and how is it calculated

Answer 2

It is the horizontal illuminance at a particular point in the room divided by the horizontal illuminance outside from an unobstructed (overcast) sky x 100%. This value varies at different points in the room and will be lower the further you are from windows. This value is fixed so does not vary with sky conditions.

Question 3

Explain outdoor illuminance

Answer 3

There are tables detailing how much light unobstructed ground will receive from an overcast sky at a specific location at specific times and dates. This is used to calculate the daylight illuminance in a room.

Question 4

Explain the concept of the average daylight factor

Answer 4

to assess the overall potential benefit of daylight to a room we calculate an average daylight factor. (TA_wØ)/A(1-R²) T=transmission of glazing taking account of dirt and blinds. A_w=area of the glazing. Ø is the angle in degrees subtended in the vertical plane by visible sky at a point in the centre of the window. A= total area of internal room surfaces. R= area-weighted average internal reflectances.

Question 5

What are the three components of daylight?

Answer 5

Light received directly from the sky, light reflected of external surfaces such as other buildings, light reflected of surfaces within the room,