Determination of light factor

1. Measure the glass area of the windows in the room (window frames shouldn’t be considered).

2. Calculate the glass area.

3. Determine the total area of the room.

4. Divide the glass area of the windows by the area of the room.

5. Express the light factor as a common fraction. To do so take 1 as the numerator by dividing the numerator and the denominator by the nominator value.

Standard light factor is as follows: in patient care institutions it is 1: 4-1: 6; in residential buildings - 1: 8-1: 10.

This method of estimating the light factor is rather simple, however, it has some limitations. It does not consider orientation of buildings, dimming caused by opposite buildings and/or trees, etc.

The estimation of natural lightning considering the shape and location of windows, height of the opposite buildings, the distance from a workplace to the window involves determining entrance angles, i.e. the aperture angle and the angle of incidence.

Natural values of tangents (see appendix page 114).

Determination of the angle of incidence (see appendix page 123)

1. Measure the horizontal distance from the workplace to the window (L).

2. Measure the height of the window.

3. Determine the ratio H: L = tg.

4. Determine the angle of incidence of light as the tangent of an angle (You can take the “Table of natural values of tangents” in the lab Assistants’ Office).

The standard angle of incidence of the workplace should be no less than 27º.

The more the angle of incidence, the better lit the room is. The further the desk is from the window, the less the angle of incidence is. Hence, it is more poorly lit.

Determination of the aperture angle (see appendix page 124)

1. Determine the minor angle. The student should sit at a desk and visualize drawing a line from the surface of the desk to the highest point of the opposite building which can be seen through the window. Another student should mark a certain point on the glass of the window through which this line passes. The student should measure the vertical distance from the plane of the window-sill to the given point. Then, the ratio of this distance to the horizontal distance from the workplace to the window which was determined when we calculated the angle of incidence should be calculated. It is the tangent of the minor angle. The value of the minor angle should be determined according to the “Table of natural values of tangents”.

2. Determine the aperture angle. It can be calculated using the following equation: Aperture angle = Angle of incidence – Minor angle

The standard aperture angle should be no less than 5º.

The greater the sky area seen from the window, the more the aperture angle is. Hence, the room is better lit.