Different quantities

Illuminance is expressed in lux and refers to incident luminous flux per unit area. Luminance is expressed in candelas per square metre and accounts for viewing direction. Both help explain workplace lighting, but they answer different questions and must not be used as synonyms.

A desk may receive enough light

Two surfaces under similar illuminance can look very different because of their finish, colour and reflectance. Light-coloured paper and a dark component do not create the same visual conditions. A glossy surface may also reflect a light source towards the eyes. Increasing light therefore does not always resolve reading difficulties or visual discomfort.

Instruments and measurement position

A lux meter measures illuminance on a plane. Luminance is measured with a luminance meter directed towards the surface or source from a defined position. Viewing geometry matters. A lux reading must not be converted into luminance through a general rule without knowing the optical properties and conditions needed to justify that relationship.

Contrast and glare

A task requires details to be distinguished, which depends on contrast with the background and surroundings. Excessive luminance differences can hinder visual adaptation. Reflections on screens can also reduce useful contrast. Assessment observes how the work is performed: eye position, windows, luminaires, screens and materials, as well as measured values.

An inspection workstation example

At a hypothetical workstation, a metal part is inspected. The lux meter shows an apparently adequate level, but the luminaire is reflected exactly where the defect is being sought. Changing orientation, diffusing light or modifying the surroundings may help more than adding power. Verify the solution with the actual part and working position.

Using both quantities preventively

A clear report identifies the quantity measured, instrument used and decision it supports. It also describes shadows, uniformity and task characteristics. Numerical criteria must match the applicable technical framework. Maintaining this distinction avoids accepting a workstation merely because it reaches a lux value while adverse visual conditions remain.