The use of visual display terminals over recent years has increased considerably and is continuing at an amazing rate as companies become aware of their need to handle the demands of everyday business with additional computer equipment.

Companies also need to be aware of their responsibility to provide a healthy and safe environment for their employees whilst using computer equipment. To maintain employees eyesight whilst using computer screens should be as important to the employer as the job in hand, and consequently an increasing number of companies have been successfully sued due to damaged eyesight caused by VDT use in areas with improper and inadequate lighting.

The chartered Institute of Building Services Engineers (CIBSE) lighting guide LG3 details the requirements for correct lighting in areas where VDT's are used and provide recommendations. The selection of luminaires in these areas should consider a 450 lux lighting level and the amount of computer screen use. It is necessary to determine the size and type of luminaire and also the category of louvre required, these are categorised as Categories 1, 2 & 3. The categories refer to the limitation of luminance above the angles of 55°, 65° and 75° to the downward vertical.

Category 1 (55°)

Category 1 luminaires are used in areas where a high density or VDT's are in use for long periods of time or where errors are critical. These areas would include banking halls, Control rooms and areas using large or old poor quality screens.

Category 2 (65°)

Category 2 luminaires are found in areas where there is still a large volume of VDT's but their usage is not as continuous as in Category 1 applications, also in areas where positive contrast displays are used in place of the usual negative contrast displays. The Category 2 louvre is slightly more efficient than in Category 1 and more widespread in use as a "best of all world's" solution for landlords and designers during new office refurbishments.

Category 3 (75°)

Category 3 luminaires are suitable for areas such as corridors, receptions and areas where there is a very low concentration of VDT's in use.