As a general rule of thumb, daylighting in all types of building should be designed to provide adequate light levels in the room and on the work plane so that daylight is the main/or only source of light (autonomous) during daytime.
For domestic properties, whilst there is little guidance on specific illumination levels in design, there is enough evidence to indicate that illuminances in the range of 100 to 2500 lux are likely to result in significant reduction of electrical lighting usage.
The light variation within your field of view can influence visual comfort and performance. For good visibility, some degree of uniformity of light is desirable. Poor visibility and visual discomfort, such as glare, may occur if the eye is forced to adapt too quickly to a wide range of light levels.
Too high or too low contrasts can also result in tiredness, headaches, discomfort etc. While specific guidelines for dwellings are not available, it is believed that luminance variations around 10:1 are suitable for daylighting design.
Generally, the human eye can accept greater luminance variations when spaces are lit by daylight than when they are artificially lit.
Until the late 1990s, lighting recommendations were based primarily on lighting needs for vision. In recent years, the lighting community has adopted a broader definition of lighting quality including human needs, architectural integration, and economic constraints, as per the diagram shown here.
For more information NARM’s NTD 12 Technical Document, entitled ‘An introduction to natural daylight design in domestic properties‘ makes useful reading.
