The human eye responds to different light levels by adjusting the iris to regulate the amount of light transferred to the retina through the pupil. This process and the time it takes for our eyes to adjust, affects our ability to perceive the detail of our environment. At night, the level of light, the contrast between various objects or light sources, and the time it takes our to eyes respond to changes (or different levels) in light, affect our ability to see. The impact of artificial light on our ability to see varies between individuals according to differences in age and vision capability. At low light levels, it is difficult to perceive colours accurately.
Glare is experienced where a light source creates visual discomfort or reduces human vision. This can be a result of light intensity, contrast or change in light level that is too rapid for the eye to adapt. Discomfort glare is defined as making vision uncomfortable or navigation difficult. Disability glare is when it is difficult for people to perceive their environment accurately or navigate it safely. The threshold between discomfort and disability glare varies according to differences in age and vision capability. Beyond the impacts on human vision, glare is also a form of light pollution that represents wasted energy.
The safety of people walking, cycling and vehicular road users, is a fundamental concern in the design of all outdoor lighting. However the provision alone of outdoor lighting may not fully meet the community's expectations of safety. The ability of people to see and be seen at night is affected by many factors such as lighting intensity, direction, uniformity, glare, and colour rendition.
The perceived and actual level of security within an area is strongly characterised by lighting. The intensity, angle and distribution of lighting affect our ability to perceive our surroundings which is important in creating secure environments.
Policy Objective 3: Lighting must provide a safe night time environment for residents of, and visitors to the National Capital.