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 | | A NEW TOOL FOR VISUAL CONTRAST | | | Laidlaw Solutions Ltd | | 06/10/2008 | | | In recent years, the needs of those with sight problems have prompted the requirement to ensure that elements such as door furniture, handrails and balustrades are clearly distinguishable.
This need for visual clarity is not entirely new. As far back as 1992, Approved Document M made reference to stair nosings needing to be “distinguishable through contrasting brightness” while in the 2001 edition of BS 8300 the expression “contrasting colour and luminance” was preferred in relation to recommendations for the blind and partially sighted.
For people with adequate vision, differences in the nature of the colour or its intensity are sufficient. The problem is that many who are partially sighted cannot use colour alone to determine visual contrast. For them, the feature of a surface that appears to be strongly associated with ability to distinguish visual differences is its light reflectance value (LRV). This is particularly true of small objects on a larger background surface, such as a lever handle on a door.
In the 2004 edition of Part M and the 2005 amendment of BS 8300, the preferred way of expressing guidance on visual contrast became by reference to a difference in LRV. LRV was defined as “the total quantity of visible light reflected by a surface at all wavelengths and directions when illuminated by a light source”. Adequate visual contrast is achieved with a difference in light reflectance values of 30 points on a 100 point scale (with jet black equivalent to zero and a perfect white 100). However, it is worth remembering that, for all practical purposes, readings of zero and 100 are considered to be unachievable. Some evidence suggests that LRV’s of as little as 20 points may be acceptable, but differences of less than 20 points are certainly insufficient.
So how is LRV measured and how can designers be confident that, when a value has been determined it is reliable? Traditional sources of information about the visual characteristics of building materials and products such as literature, websites and colour swatches are susceptible to inaccurate and variable colour representation and can only be considered as a visual guide. Whatever degree of colour accuracy is claimed, it cannot be used to determine whether there is sufficient visual contrast between installed building elements or against surrounding surfaces. According to Shafiq Sharif, Marketing Manager of Laidlaw Solutions Ltd, “Provision of accurate LRV data will undoubtedly be required in future. Laidlaw routinely uses a reflectance spectrophotometer to provide objective LRV assessment and will continue to do so, but the need undeniably exists for a standardised test method. Specifiers must be able assess products on known like-for-like criteria, using the same measurement technique and under the same lighting conditions”.
The BSI’s draft British Standard (BS 8493) - Light reflectance value (LRV) of a surface – Method of test has been circulated for public comment and is likely to be published later this year. The draft standard describes how the LRV can be measured for a range of different surfaces, such as those of piled carpets, painted surfaces, materials with opaque coatings, and reflective finishes. It can also be used for materials with non-opaque coverings such as veneered timber doors finished with a wood stain and metallic products such as brushed stainless steel door furniture. Although the proposed test needs to be conducted on samples with a flat surface, it is thought that results will apply equally to products such as door handles with the same surface finish but a circular or oval cross section. Given the importance of access areas for the partially sighted, and the differing combinations of doorset, lever, backplate and handrails, the ability to compare LRV’s for different manufacturers’ products will be of enormous value.
To illustrate a comparison between a colour and its LRV and to help designers make an initial assessment of suitable combinations, the BS 8493 draft includes an Annex showing the LRV of colours using the proposed method from the range in BS 4800, Schedule of colours for building purposes. The draft emphasises that it is not promoting exclusive use of BS 4800 colours in order to constrain manufacturers or designers, as the method can be used to determine the LRV of a surface of any colour.
From the rather general guidance given in Approved Doc M 1992, great strides have been made in attempts to quantify the means of providing sufficient visual contrast. It is hoped that, when published, the BS 8493 standardised test method will be accepted as a valuable tool for determining accurate and comparable LRV data. Information on spectrophotometer testing for its range of doorsets, ironmongery and handrails and balustrades can be obtained meanwhile from Laidlaw Solutions on 01902 600431. | |
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