In the UK, CIBSE Lighting Guide 10 (2014) recommends the following values:
<2 DF – Underlit, artificial light will be required to supplement
2 – 5 DF Adequate daylight, artificial light may be required some of the time
>5 DF Well lit, artificial light is generally not required but there may be glare and excessive solar gain
LEED (Leadership in Energy and Environmental Design), suggests that daylight factor be a minimum of 2% in spaces used for critical visual tasks.
BREEAM (Building Research Establishment Environmental Assessment Methodology), suggests that a minimum of 80% of the floor area in occupied spaces has an average daylight factor of 2% or more.
Users are advised to check the guidance applicable to their regions.