ISO 20351:2024

International
Standard
ISO 20351
Second edition
Fine ceramics (advanced ceramics,
2024-10
advanced technical ceramics) —
Test method for optical properties
of ceramic phosphors for white
light-emitting diodes using an
integrating sphere
Reference number
© ISO 2024
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Published in Switzerland
ii
Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Measurement apparatus . 2
4.1 Apparatus configuration .2
4.2 Light source unit .4
4.3 Sample unit .4
4.3.1 Cell .4
4.3.2 White diffuser or reference cell .4
4.3.3 Integrating sphere .4
4.4 Detection unit .5
4.4.1 Directing optical system .5
4.4.2 Spectrometer and detector .5
4.4.3 Amplifier .5
4.5 Signal and data processing unit .5
5 Calibration, inspection and maintenance of measurement apparatus . 5
5.1 General .5
5.2 Wavelength calibration of light source unit .5
5.3 Cells and cover glasses .5
5.4 Integrating sphere walls and white diffusers .5
5.5 Wavelength calibration of detection unit .5
5.6 Spectral responsivity correction .6
6 Samples . 6
6.1 Reference material .6
6.2 Storage and pre-processing .6
6.3 Filling cells with samples .6
7 Procedure, calculation and report for absolute measurement . 6
7.1 Measurement method .6
7.1.1 Measurement environment .6
7.1.2 Light spectrum without phosphor sample .7
7.1.3 Light spectrum with phosphor sample .7
7.2 Calculations .7
7.2.1 Conversion to photon-number-based spectra .7
7.2.2 Fluorescence spectrum .8
7.2.3 Internal quantum efficiency .8
7.3 Test report .8
8 Procedure, calculation and report for substitution measurement . 9
8.1 Measurement procedures .9
8.1.1 Measurement environment .9
8.1.2 Spectrometer setup for substitution measurement .9
8.1.3 Measurement for reference material .10
8.1.4 Measurement for phosphor material under test .10
8.2 Calculation .10
8.2.1 Spectral responsivity correction .10
8.2.2 Conversion to photon number-based spectral distribution .10
8.2.3 Calculation of scattered light and fluorescence photon numbers .11
8.2.4 External quantum efficiency . 12
8.2.5 Absorptance . 12
8.3 Test report . 12

iii
Bibliography . 14

iv
Foreword
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This document was prepared by Technical Committee ISO/TC 206, Fine ceramics.
This second edition cancels and replaces the first edition (ISO 20351:2017), which has been technically
revised.
The main changes are as follows:
— scope of the document is expanded by additionally implementing the reference material-based
substitution measurement method to measure external quantum efficiency and absorptance.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.

v
Introduction
White light-emitting diode (LED) based solid-state lighting (SSL) has been widely used for a variety of
applications as alternatives for incandescent and fluorescent lamps. Initially, white LEDs (comprising blue
LEDs and yellow phosphors) became popular as backlight sources for small-size liquid-crystal displays
(LCDs) used in mobile phones and digital cameras. These were followed by white LEDs (consisting of
blue LEDs combined with green and red phosphors) applied to backlight sources for large-area LCDs.
Subsequently, LED lamps were commercialised for general lighting, replacing conventional luminaires and
capitalising on their advantages, such as compactness, high luminous efficiency, high
...