3Further Reading: Douglas J & Ryan M (ibid.)
4Further Reading: Thomas M (1991) Vision, motivation and movement. Focus 3:12-15.
There is no hard and fast rule as to what is meant by dim versus good light. "Dim" does not mean "dark" - we all experience poorer mobility in a dark room! It is more of a qualitative judgment. If you and others get around easily in dim light but the learner's mobility is quite different from that in good light, there may be several reasons. If this has suddenly occurred you should investigate further.