Aims The aim of this work was to construct a lighting device that allows a uniform lighting of top illumination charts, as used for the examination of contrast vision and visual acuity. The relevant standards make strict demands for such charts with regard to the quality of the lighting, the absolute brightness and the uniformity of the luminous intensity distribution over the chart surface. If measurements are made under differing daylight conditions or if artificial light sources are installed in the examination room, as frequently practiced, then these requirements cannot be fulfilled.
Methods A lighting device was developed using daylight spectrum tubes installed on the right and left sides of the chart. The tubes were shielded by opaque diffusers to scatter the light.
Results The device produced an accurate and uniform distribution of luminance at 21 points over the chart that was not obtained with overhead lighting running parallel or horizontal to the chart.
Conclusion A uniform illumination of top illumination test charts was achieved allowing adherence to the standards for measuring acuity set out by the European Union and enabling comparison of such visual examinations in multi-centre clinical studies.
- Contrast vision
- visual acuity charts
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Competing interests None.
Provenance and peer review Not commissioned; externally peer reviewed.