Coloured filters are designed to help individuals who suffer from a condition known as visual stress. People with this condition are especially sensitive to lights, glare, patterns, colours, and contrast.
Coloured filters are designed to block the specific wavelengths of light to which an individual is sensitive. So, for example, an individual might be especially sensitive to blue light and therefore use a blue filter to reduce its effects.
There are several types of coloured filters including overlays and lenses. Coloured overlays are clear plastic sheets that can be placed on top of reading materials, such as books or newspapers. Coloured lenses are tinted, non-optical lenses which can be put into spectacle frames.
Some people believe that coloured filters can be used to help people with autism who suffer from visual stress, leading to improvement in their visuospatial abilities. This may in turn lead to improvements in other areas, such as reading ability.