BS EN 4705:2020 pdf download
BS EN 4705:2020 pdf download.Aerospace series – Measurement methods regarding the lifetime behaviour of light units in a standardized aircraft-related environment.
4.3 The brightness of the light unit falls below a defined limit
The brightness decreases during lifetime. When it decreases below a defined limit the light unit does not fulfil the specification and the light unit shall be considered as faulty. The definition of the limit depends on the user case of the light unit.
For light units in the aircraft cabin, if not otherwise specified, a brightness decrease to 70 % of the initial value is considered as the limit
4.4 The chromaticlty of the light unit Is out of a defined limit
If the light unlts chromaticity is out of the specified hmlts the unit Is considered as failed.
The extent of chromaticity shift Is given in SDCM or in the chromaticity coordinate distance .dF by EN 4706.
For light units in the aircraft cabin, if not otherwise specified, a chromaticity shift shall not exceed iiF =3 SDCM
S Failure mode identification
5.1 General
This document refers to failure modes as given in 4.1 b) and 4.1 c) only.
The behaviour of light units regarding lifetime shall be evaluated by testing. To minimize test duration an appropriate extrapolation model shall be applied.
Unless otherwise specified predictions according to this document shall be made with a confidence level of 95%.
5,2 Brightness degradation calculation selection
The brightness degradation can be approximated by different fitting functions depending on the technology of the light unit. The selected method and the achieved accuracy shall be indicated by the manufacturer. One recommended method based on testing and extrapolation is described in
IES i.M 80/TM 21.
5.3 Colour degradation
The major contributor regarding colour degradation is operation time, but other parameters, namely temperature, operational current and specified colour, may have an impact
Under the given preconditions, i.e. specified target chrnmaricity and a tolerance defined by the radii of the associated MacAdam ellipse, the following shall be considered as failure case.
End of life is reached when the chromaticity shift curve intersects the borderline of the corresponding MacAdam ellipse, see Figure 2.
The colour degradation can be approximated by different functions Cxy =jt, T, I. L’5 etc.) depending on the technology of the light unit. The selected method and the achieved accuracy shall be indicated by the manufacturer.
6 Operating the light unit
6.1 General
The light unit shall be operated in an environment similar to an aircraft cabin. That means the installation position; installation condition and ambient temperature shall be similar to the operation conditions in the aircraft. Therefore some standardized test environments shall be determined, The light units shall be prevented from vibration and shock to avoid a change In light output caused by mechanical alteration. According to IES EM8O-O8 the relative humidity shall be maintained to less than 65 % throughout the life test.
The operation conditions may be dilfcrent to those in normal use, e.g. It is possible to drive light sources like L.EDs continuously during lifetime test when switching on and off does not influence the lifetime performance. Each light unit under test shall be marked with its part number and serial number.
62 Installation orientation
The installation orientation of the light unit under test shall be similar to the operating location in the aircrart to consider air convection at the heat sinks, see Table 1. II multiple orientations exist, the thermal worst case orientation shall be determined and documented and shall be used for testing.
6.4 Ambient temperature
The light unit may be tested in an air-conditioned test chamber with constant ambient temperature orin a room which is exposed to annually or day timely temperature changes. The mean ambienttemperature shall be recorded and shall be added to the test records.Table 3 shows the different testcategories. In case of category C the selected temperature shall be recorded.
