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Adapting Video for VI Learners

Setting up lighting

Light Sources

Light is both a benefit and a problem. Some light sources positively aid vision e.g. computer screen or TV monitor. Others can be a source of visual irritation through glare e.g. sun streaming through a window, or a wrongly positioned angle poise lamp. Compare the choices of position below -

Glare reduction with drawn curtains

No glare sources(D)

As well as causing irritation through glare, looking towards a bright source of light will mean that anything in front of it will not be seen. Teachers and lecturers who wander around the room, sometimes stopping to sit on a radiator at a window, or standing in front of a brightly illuminated overhead projection screen will be lost to most people with visual impairment (as well as causing problems for deaf students trying to lipread!)

Teacher before window: excessive glare(D)

Pale clothing doesn't provide a good contrast to pale skin, and flat lighting from the front alone can make this worse: side lighting can help accentuate (model) facial features - but beware of going too far and producing shadows. The pictures below show both good and poor choice of clothing and lighting.

Good contrast:

Good contrast

Useful modelling:

Soft side light

Too much side lighting:

Harsh side light and deep shadows

Flat lighting and pale clothing reduce contrast:

Flat lighting and white clothes - poor contrast

Students are usually at the mercy of the lecturer regarding the lighting in a room or lecture theatre. If the lighting conditions are too extreme, it would be worthwhile for the student to discuss the situation with the lecturer to agree a solution. Most lecturers (although not all!) are reasonable. Normally, well-lit conditions are necessary for coming into and out of rooms - tiered lecture theatres can be very dangerous if there is not sufficient light to see the steps.

If lights have to be lowered for slides or videos, some students with visual impairment will need to bring their own torches to see to take notes, unless of course they are Braille users or touch typists. Some lecturers do not bother to raise the lighting level while they are speaking in breaks between slides or video excerpts. They are likely to be invisible to students with low vision and unless the content is extremely lively and interesting, they may nod off!

Well directed lighting can highlight features of an object or a face by enhancing contrast and make it easier for students to make out outlines, expressions and gestures.

Light issues with specific visual field defects

Normally for watching TV there should be a good source of environmental (as opposed to individual 'task' lighting) from ceiling fluorescent lighting, the level of which can be controlled by dimmers. However, the levels of illumination will depend upon individual impairments and will be a matter of personal preference. For instance, some students may be photophobic and will prefer lower overall light levels. As a matter of safety, tutors and fellow students need to realise that those with retinal peripheral damage (eg Retinitis pigmentosa), will have great difficulty in seeing during and following a period of being in an environment with low levels of illumination.

As with all other ergonomic issues to do with VI students in mixed settings, what will be right for one student will make life difficult for another.

For students who have problems seeing detail, the dominant light source should come from behind them. However, you then need to be especially careful to avoid placing monitors so that natural or artificial light is reflected in the screen.

Glare is light that is not useful; it comes from oblique sources and enters the periphery of the eye, thus increasing the background illumination and decreasing contrast. It causes fatigue and strain and visual disability. Some students are especially sensitive to glare. You need to ensure that light sources don't shine directly into students' eyes eg sunlight through windows with poorly fitting blinds. You also need to ensure that lighting is even, with as few highlights as possible. Watch out for reflective surfaces, bright OHP lights, and light 'leaking' from slide projectors. Monitors also need attention, both the level of brightness of the student's screen, and hot-spots from other sources. What is just an irritation to a person with good sight may make seeing impossible for a partially sighted student.

Simulation of effects of glare for VI student(D)

Colour complicates the issue, and forces other compromises. Any deviation from a normal brightness range (on screen or in ambient conditions) also affects colour. Dusk or excessive brightness affect everyone, but especially those who already have colour perception problems. So while you are setting up your lighting for appropriate overall brightness and trying to avoid unwanted glare, you also need to check that the balance you strike does not unduly reduce the effective range of colour or contrast.

Students whose field of vision is narrow and those who have difficulty following moving objects can be particularly affected by localised high spots, so pay particular attention to any possible dazzling sources causing glare either directly or by being reflected off the screen.

 
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