Lighting and Colour

Seating

A-1. The student, the specialist teacher, and at times, the parent(s) of the visually impaired will help the teacher determine where the student should best be seated in the classroom (ADE, 1996)

A-2. Seat the student in a location with which s/he is comfortable and is able to make the best use of “functional vision” (ADE, 1996, p. 11). For example, if a student is using telescopic lenses or a monocular to see from far away, then sitting at the back of the room is a better position (Sewell, 2005).

Workspace

A student may need extra workspace for any specialized equipment or technology needs. Also, have the electrical wiring evaluated for the student’s necessary assistive technology (NCSDPI, 1998).

Glare

Be aware of glare. The North Carolina State Department of Public Instruction states that, “Glare should be eliminated (e.g. special dry marker board surfacing) or controllable (e.g. by blinds, shades, indirect lighting and window location)” (NCSDPI, 1998, p. 23). Consider adjustable lighting so that certain parts of the room may be lit while others are darkened (NCSDPI, 1998). D. Colour Contrast (Elmwood Visual Resource Centre, Christchurch, New Zealand)

Colour Contrast

Author: Elmwood Visual Resource Centre, Christchurch, New Zealand

Effective Colour Contrast
Designing for People with Partial Sight and Colour Deficiencies by Aries Arditi, Ph.D.

This brochure contains basic guidelines for making effective colour choices that work for nearly everyone. To understand them best, you need to understand the three perceptual attributes of colour: hue, lightness and saturation, in the particular way that vision scientists use them. Full explanations of these terms are provided in the pages that follow.

How does impaired vision affect colour perception?
Partial sight, aging and congenital colour deficits all produce changes in perception that reduce the visual effectiveness of certain colour combinations. Two colours that contrast sharply to someone with normal vision may be far less distinguishable to someone with a visual disorder.

image showing high contrast vs low contrast

Exaggerate lightness differences between foreground and background colours, and avoid using colours of similar lightness adjacent to one another, even if they differ in saturation or hue.

image showing effective contrast vs not effective contrast

Don’t assume that the lightness you perceive will be the same as the lightness perceived by people with colour deficits. You can generally assume that they will see less contrast between colours than you will. If you lighten your light colours and darken your dark colours, you will increase the visual accessibility of your design.

Light colors vs Dark colors

graphic of the color wheel

Choose dark colours with hues from the bottom half of the hue circle against light colours from the top half of the circle. Avoid contrasting light colours from the bottom half against dark colours from the top half.

another examples showing light non effective contrast using light pink and light green

For most people with partial sight and/or congenital colour deficiencies, the lightness values of colours in the bottom half of the hue circle tend to be reduced.

Contrasting hues

image showing how to choose effective colors from the color wheel

Avoid contrasting hues from adjacent parts of the hue circle, especially if the colours do not contrast sharply in lightness.

image showing example of non effective adjacent hue colors

Colour deficiencies

Colour deficiencies associated with partial sight and congenital deficiencies make it difficult to discriminate between colours of similar hue. Hue, lightness and saturation - the three perceptual attributes of colour - can be envisioned as a solid.

graphic showing low lightness versus saturation

Hue Variations

Hue varies around the solid; lightness varies from top to bottom and saturation is the distance from the centre.

color wheel

Hue is the perceptual attribute associated with elementary colour names.

Hue enables us to identify basic colours, such as blue, green, yellow, red and purple. People with normal colour vision report that hues follow a natural sequence based on their similarity to one another.
With most colour deficits, the ability to discriminate between colours on the basis of hue is diminished.

image showing light and color

Lightness corresponds to how much light appears to be reflected from a surface in relation to nearby surfaces.

Lightness, like hue, is a perceptual attribute that cannot be computed from physical measurements alone. It is the most important attribute in making contrast more effective.
With colour deficits, the ability to discriminate colours on the basis of lightness is reduced.

image demonstrating saturation

Saturation is the degree of colour intensity associated with a colour’s perceptual difference from a white, black or grey of equal lightness.

Slate blue is an example of a desaturated colour because it is similar to grey. A deep blue, even if it has the same lightness as slate blue, has greater saturation.
Congenital and acquired colour deficits typically make it difficult to discriminate between colours on the basis of saturation.

graphic showing how the color brown is used on light purple versus dark puprle

To a person with colour-deficient partial sight, the left-hand panel might appear like the right-hand panel appears to a person with normal colour vision.

With colour deficits, ability to discriminate colours on the basis of all three attributes - hue, lightness and saturation - is reduced. Designers can help to compensate for these deficits by making colours differ more dramatically in all three attributes.