INTERNATIONAL ISO/CIE STANDARD 23539 First edition 2023-03 Photometry - The CIE system of physical photometry Photométrie - Le systeme CIE de photometrie physique Reference number IS0/CIE 23539:2023(E) cie @ IS0/CIE 2023 IS0/CIE 23539:2023(E) COPYRIGHT PROTECTED DOCUMENT IS0/CIE2023 All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on the internet or an intranet, without prior written permission. Permission can be requested from either Iso at the address below orIso's memberbody inthecountryoftherequester ISO copyright office CIE Central Bureau CP 401 : Ch. de Blandonnet 8 BabenbergerstraBe 9/9A · A-1010 Vienna CH-1214 Vernier, Geneva Phone:+41227490111 Phone: +431714 3187 Fax: +4122749 09 47 Email: copyright@iso.org Email: ciecb@cie.co.at Website: www.iso.org Website: www.cie.co.at Published in Switzerland i @ IS0/CIE 2023 - All rights reserved