At Asco Light’s we seek to use our industry leading expertise by providing fantastic lighting solutions for individuals with visual impairments. With such projects requiring special consideration and detail, principles must be followed to create perfect lighting.
For premises to be occupied by individuals with a visual impairment, some adjustment to recommended task illuminances will be appropriate. In addition, sudden changes in illuminance should be avoided to prevent adaptation difficulties. With visual impairment light transmission qualities of the eye are damaged and It is therefore very important to minimise glare. The aim of the project should be to use light to incorporate the health, comfort and wellbeing of an individual.
Important aspects of lighting for people who are visually impaired
For many visually impaired individuals, an increase in illuminance will lead to increased visual performance. However, for a significant minority an increase in general illuminance will actually lead to reduced visual performance. It is therefore normally wise not to increase the average maintained illuminance in a space significantly above the figure recommended by the Society of Light and Lighting, but instead to provide localised or task lighting to assist those who find it useful.
If the type of visual impairment is known, e.g. for an individual in their own home, the illuminance can be adjusted as appropriate. However, even if the overall illuminance is increased to facilitate perception of the boundaries of the space, furniture and movement around the room, localised lighting for specific tasks will still normally be appropriate. Ensure that stairs, ramps and slopes are lit so that they can easily be identified when approaching in either direction. Low level lighting can put light onto the treads without glare. Glare should be strictly controlled, whatever the type of visual impairment. Light sources should always be shielded from view at normal angles. Task lights should be chosen which provide good shielding of the source.
Colour rendering – Colour and luminance contrast
Just as important as the lighting itself is the choice of decor and ensuring that there is colour and luminance contrast between, e.g. doors and their handles. Building Regulations give a requirement for contrast between doors, door furniture and door edges, and uses the term ‘contrast visually’. However the criterion is based on laboratory measurements, and does not take into account the colour rendering properties of the light source present in the actual room or space. To assist colour discrimination, the colour rendering index of the light source should be at least Ra80, the recommendation for most interiors, and where feasible, lamps of Ra90 should be used. Fluorescent lamps with this colour rendering performance are readily available, as are some metal halide lamps. Colours for doors and doorframes should be chosen to provide good colour and luminance contrast. Door furniture should be chosen which contrasts well with the door. Doors should not be the same colour as the walls in which they are set. The same principles apply when choosing handrail colours in order to provide contrast with the background wall. To aid orientation and navigation, floors and walls should not be the same colour, nor should walls and ceilings.
Proper Use of Natural light
Natural light is important for personal health and can influence mood, sleep and motivation. Daylight is important to the body’s circadian system, which controls daily and seasonal body rhythms, and is linked to various functions of the body (e.g. the sleep/wake cycle, and changes in core body temperature and in hormone secretion). Disruption to this system from lack of light can cause problems such as depression and poor sleep quality, which could lead to more serious problems.
Most people express a preference for windows and natural daylight in their homes. Windows can give occupants a sense of connection to the outside world. Many people with partial sight can detect changes in weather, season and time of day, or be aware of the presence of human activity outside. People with sight loss often appreciate this sense of connection to the external environment.
Daylight is usually greater near windows and reduces when moving further away. However, obstructions to windows may reduce the amount of daylight that can get into a room. Windows may be obstructed internally by large objects placed on the window sill, net curtains or curtains that are not fully drawn back. Externally, windows can be blocked by vegetation. It is also important to keep windows clean. Direct sunlight can cause harsh shadows and glare that may be uncomfortable and make vision more difficult. Horizontal or vertical blinds are the best way to reduce glare and control daylight.
When considering exterior lighting, low level lighting by means of bollards which do not emit light above the horizontal will often find favour with people who are visually impaired because it provides light on the ground without glare. We can ensure that stairs, ramps and changes of level are lit so that they can easily be identified when approaching in either direction. Our design will make sure lights over entrances and exits should not emit glare to those entering or leaving the building. We shall also consider the need to provide a gradual reduction in illuminance from inside to outside at night. This will allow the extended adaptation times of people who are visually impaired to be accommodated.