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2.6 Linearity
The manufacturer must specify the linearity of response within the specified measuring range.
2.7 Temperature dependence
The manufacturer must specify the measuring instrument’s temperature dependence.
Unless the manufacturer states otherwise, the temperature dependence test is conducted by measuring the lux metre’s readout at temperatures of 5 °C, 25 °C (reference temperature) and 40 °C.
2.8 Other supplementary characteristics
The photometric head’s sensitivity to UV radiation and infrared radiation, the lux metre’s polarisation responsivity and the influence of modulated radiation may be specified as supplementary characteristics.
3 Technical requirements
3.1 General
Lux metres must be of solid construction and must be manufactured from suitably strong and sturdy materials in order to withstand the normal conditions of use and environments they are subjected to without malfunctioning or suffering undesired changes in their metrological parameters over time.
3.2 Photoelectric transducer
The photoelectric transducer must be designed so that it cannot be damaged during normal cleaning.
In the case of lux metres in which the transducer’s protective housing is made up of parts which conduct electricity and the insulation resistance value (resistance between the internal wiring and the sensor housing) may affect the lux metre’s metrological properties, the manufacturer must specify the insulation resistance value in the technical documentation.
3.3 Display device
The analogue display device of a lux metre must have a graduation value of ≤ 5 lx.
The digital display device of a lux metre must have a resolution of 1 lx or better. The numbers on the digital display must be larger than 4 mm.
The unit of measurement for illuminance is 1x.
The outer covering must safely protect the display device from exterior effects which occur during the measuring of illuminance (primarily from moisture condensation).
With devices having dials, all technical information on the device specified on and around the scale must be clear and intelligible.