Daylight Factor in the Energy Efficiency Calculator OKNA.ua

Daylight factor is defined as the ratio of the illuminance on the indoors working plane to the external unobstructed illuminance under overcast sky. Average Daylight Factor (ADF) measured in %.

ADF depends on:

• ● Window area
• ● Floor area
• ● Glazing area
• ● Profile area
• ● Orientation
• ● Shading

How ADF is calculated in the Energy Calculator OKNA.ua

Building standards provided for glazing with a ratio of 0.18 in 60-90 yy. This ratio corresponds to most apartment buildings. So Energy Calculator OKNA.ua uses a default glazing ratio of 18%. But you can specify the your floor area (room) in the "Floor area" field.

If the room has two windows, the floor area should be divided into appropriate parts.

ADF is compared to

Average Daylight Factor for living rooms, bedrooms, dormitory rooms, kitchens (2%), children's rooms (2.5%), cabinet, libraries (3%) should be 2.5% according to ДБН В.2.5-28:2018 «Природне і штучне освітлення» (.pdf).

Over time, the glass becomes dirty and its light transmission decreases. Therefore, the ДБН introduced a stock factor for natural light. It is, in the case of glass washing twice a year, 1.2.

ADF, taking into account the stock factor for glass dusting, is:
2.5% * 1.2 = 3%

So, ADF is compared with 3% in the Energy Calculator OKNA.ua.

Daylight Factor < 2% – Room looks gloomy, electric lighting needed most of the day.

Daylight Factor 2-3% – Room has daylight appearance. Artificial lighting required on occasion. If the average daylight factor is 3%, then electric lighting rarely needed.

Daylight Factor > 5% – Room has strong daylight appearance, but thermal issues may arise.