In the presence of glare, the iris in the eye closes down, and vision at low lighting levels is not as good as without the glare source. Another important issue is transient adaptation, which refers to the time it takes the eye to adjust in going from bright levels of lighting to faint ones, and vice versa. One must also be conscious of the level of the ambient lighting. All of these items, and others, must be taken into account in investigating vision at low lighting levels. No one item operates in isolation from the others.
Vision is different at low lighting levels than at high levels.
Avoid glare, and do not overlight. We will summarize this issue by quoting from a recent paper by Werner Adrian, who has done extensive research in the area. With decreasing luminance levels, the spectral sensitivity of the eye changes and it becomes more blue sensitive. This goes in concert with the fading of colors until, in low levels, we perceive brightness only. A photometric quantity that accounts for the changing spectral sensitivity of the eye is called the Equivalent Luminance, L eq .