Visual safety of quartz linear lamps

A quartz linear lamp (QLL) is a compact infra-red (i.r.) heating lamp. It consists of a tungsten filament in a quartz envelope, which for space heating purposes is surrounded by a ruby coloured filter. The filament runs at about 2400 K and produces i.r. radiation with a peak output at 1200 nm. The lamps are widely used for space heating and are normally fitted with a parabolic reflector. There are no statutory criteria for potential visual hazards resulting from the use of such lamps in the U.K. The ACGIH has produced a provisional set of rules on light and near i.r. This paper reviews potential hazards to the eye in the context of the ACGIH rules and the output of QLL heaters. The heaters produce no u.v. or blue light hazards. The brightness and heat of the lamp is sufficient to produce an aversion response which will prevent retinal thermal damage from inadvertent viewing. The probability of retinal thermal injury from an i.r.-A image focused on the retina is examined and it is shown that there is no risk at normal viewing distances. To prevent any risk of cataractogenesis, the rules provide for an upper limit of irradiance (TLV) at the eye of 100 W m-2 in the i.r.-A band; the paper examines the potential hazard from longer wavelengths and concludes that they do not present a hazard with this type of heating. The conclusion is that QLL heaters used for space heating in accordance with manufacturer's instructions present no hazard to the eye.