EN 4705-2020 pdf download.Aerospace series – Measurement methods regarding the lifetime behaviour of light units in a standardized aircraftrelated environment.
3.6
chromaticity coordinate
two-dimensional data representation of the colour in the corresponding colour space, e.g. x andy for the
CIE 1931
3.7
MacAdam ellipse
area in the corresponding colour space (e.g. CIE 1931) in which all colours have the same visual impression to an observer as the colour in the centre of this area
Note 1 to entry: The borderline of the ellipse represents the just noticeable colour difference. Based on experimental data, originally 25 MacAdam ellipses were defined in the CIE 1931 colour space. In the experiment an observer had a given colour and was able to modify the chromaticity locus of a second colour. The chromaticity mci, where the observer determined a difference between the two colours were recorded. When all these points were plotted in the CIE 1931 diagram, they created an ellipse around the chromaticity locus of the given colour. The size and the orientation of the ellipses are different for different colours.
[SOURCE: D. L MacAdam]
3.8
Standard Deviation of Colour Matching
SDCM
for a given target chromaticity locus, the metric of the distance between light colours at photopic light level, that describes approximately the perceptual distance between two chromaticity loci as a multiple of the MacAdam ellipses for these chromaticity loci
Note ito entry: n SDCM means that the distance between the two chromaticity loci Is n-times the radius of the appropriate MacAdam ellipse in that direction. The centre of the ellipse is given by the chromaticity locus of the specified colour. Two chromaticity loci on opposite points of the MacAdam ellipse have a distance of (2 n) SDCM, The SDCM calculation between two chromaticity loci may be non-linear, dependent on the selected colour space. Therefore distances are limited to less than 10 SDCM.
Note 2 to entry: For this document the calculated data Iron) the MacAdam ellipses has been used.
3.9
chromatlclty coordinate distance
perceived chromaticity coordinate distance between any chrornaticity loci and the target chromaticity locus in the corresponding colour space which is expressed in SDCM values
Note Ito entry: The maximum chromaticity coordinate distance between any two chromaticity loci is the full diameter 2 x R of the corresponding n-times scaled MacAdam ellipse:
4.4 The chromaticity of the light unit is out of a defined limit
If the light unit’s chromaticity is out of the specified limits the unit is considered as failed.
The extent of chromaticity shift is given in SDCM or in the chromaticity coordinate distance zlF by EN 4706.
For light units in the aircraft cabin, if not otherwise specified, a chromaticity shift shall not exceed iiF =3 SDCM.
5 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 he 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 LM 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 chromaticity 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.EN 4705-2020 pdf download.

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