Colorimeter and trial lenses.

Coloured glasses have been with us for at least two centuries, but it is only in the last four decades with the advent of plastic (resin) lenses that it has been possible to obtain almost any desired spectral transmission quickly and simply. The tint required for therapeutic purposes has to be selected with precision. The Intuitive Colorimeter permits the choice of colour to be made simply and quickly.

The Intuitive Colorimeter is a simple optical device that shines coloured light on a page of text and allows the user to vary the light with three controls, one for colour (hue), one for strength of colour (saturation) and one for brightness (luminance). The variation of hue and saturation is continuous. Luminance may be selected from one of four levels.

The text used as stimulus material consists of random letters arranged in strings to resemble words in a paragraph. The clarity can therefore be assessed independently of the linguistic and semantic content of the text.

An examination with the colorimeter typically consists of a preliminary assessment, followed immediately by a detailed assessment. The preliminary assessment is undertaken by comparing perception under white light with that under light of various hues, systematically selected and briefly presented. At each of 12 hues, evenly spaced around a hue circle, the saturation is increased and then decreased. The purpose is to identify any hues that have beneficial perceptual effects and, equally importantly, to identify any that are aversive. Following this initial assessment, detailed assessment is performed. The choice of beneficial hue is refined with the eyes colour-adapted. Saturation and hue are alternately optimised, saturation by method of adjustment, and hue by two-alternative forced choice from similar hues of the appropriate saturation.

The optimal colour, once selected, is replicated by a combination of tinted trial lenses, and these are worn for a period sufficient to assess their effects on the perception of surface colour, as well as on reading.

The assessment procedure described above minimises exposure to aversive hues, and it allows the tint to be selected quickly and efficiently under conditions of colour adaptation. The tint is provided by glasses with a smooth spectral transmission that minimises any change in tint under lighting having various uneven spectral power distributions.

The system for precision tinting described above is available from Cerium Visual Technologies, Appledore Rd., Tenterden, Kent, England.

You can obtain the name of a Colorimeter specialist near you if you are in the UK or elsewhere.

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