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GB/T 13987-2025 English PDF

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GB/T 13987-2025: Determination of flash guide numbers for electronic photoflash equipment
Status: Valid

GB/T 13987: Evolution and historical versions

Standard ID	Contents [version]	USD	STEP2	[PDF] delivered in	Standard Title (Description)	Status	PDF
GB/T 13987-2025	English	274	Add to Cart	3 days [Need to translate]	Determination of flash guide numbers for electronic photoflash equipment	Valid	GB/T 13987-2025
GB/T 13987-1992	English	179	Add to Cart	2 days [Need to translate]	Determination of flash guide numbers for electronic photoflash equipment		GB/T 13987-1992

Basic data

Standard ID	GB/T 13987-2025 (GB/T13987-2025)
Description (Translated English)	Determination of flash guide numbers for electronic photoflash equipment
Sector / Industry	National Standard (Recommended)
Classification of Chinese Standard	N46
Classification of International Standard	37.040.10
Word Count Estimation	14,153
Date of Issue	2025-08-29
Date of Implementation	2026-03-01
Older Standard (superseded by this standard)	GB/T 13987-1992
Issuing agency(ies)	State Administration for Market Regulation, National Standardization Administration

GB/T 13987-2025: Determination of flash guide numbers for electronic photoflash equipment

---This is an excerpt. Full copy of true-PDF in English version (including equations, symbols, images, flow-chart, tables, and figures etc.), auto-downloaded/delivered in 9 seconds, can be purchased online: https://www.ChineseStandard.net/PDF.aspx/GBT13987-2025
ICS 37.040.10 CCSN46 National Standard of the People's Republic of China Replaces GB/T 13987-1992 Determination of the guide number of electronic flash devices for photography Released on August 29, 2025 Implementation on March 1, 2026 State Administration for Market Regulation The National Standardization Administration issued

Preface III Introduction IV 1 Scope 1 2 Normative references 1 3 Terms and Definitions 1 4 Guide Number Calculation Formula 1 5.How to express the guide number 2 Appendix A (Informative) Conversion of Flash Guide Number from Metric to Foot 3 Appendix B (Informative) Explanation of the Flash Index Formula 4 References 6 Preface This document is in accordance with the provisions of GB/T 1.1-2020 "Guidelines for standardization work Part 1.Structure and drafting rules for standardization documents" Drafting. This document replaces GB/T 13987-1992 "Determination of the guide number of electronic flash devices for photographic use" and is consistent with GB/T 13987-1992. In addition to structural adjustments and editorial changes, the main technical changes are as follows. --- Changed the scope of the content (see Chapter 1, Chapter 1 of the.1992 edition); --- Changed the terms and definitions of “Flash Guide Number” and “ISO Flash Guide Number” (see Chapter 3, Chapter 3 of the.1992 edition); --- Changed the value of k and the calculation formula in formula (1) (see 4.1, 4.1 of the.1992 edition); --- Deleted the content related to the measurement of flash index (see Chapter 5 of the.1992 edition). This document is equivalent to ISO 1230.2007 "Determination of the guide number for photographic electronic flash devices". This document adds a chapter on “Normative References”. The following minimal editorial changes have been made to this document. --- The name of the standard is changed to "Determination of the Flash Guide Number of Electronic Flash Devices for Photography". Please note that some of the contents of this document may involve patents. The issuing organization of this document does not assume the responsibility for identifying patents. This document was proposed by the China Machinery Industry Federation. This document is under the jurisdiction of the National Technical Committee for Standardization of Photographic Machinery (SAC/TC107). This document was drafted by. Hangzhou Photographic Machinery Research Institute Co., Ltd., Hangzhou Guozhao Testing Technology Co., Ltd., Changzhou Meitu Photographic Equipment Co., Ltd., Dace Technology (Guangzhou) Co., Ltd., and Shenzhen Qiuyu Electronic Technology Co., Ltd. The main drafters of this document are Hu Xiaoying, Wang Wei, Hu Lihua, Wang Jun, Huang Yizhao, Wen Zhong, and Jiang Qiuxiong. The previous versions of the documents replaced by this document are as follows. ---First published in.1992 as GB/T 13987-1992; ---This is the first revision.

introduction

In general flash photography, the flash light source is mounted on the camera, and the camera is sensitive to the ISO of the film or digital camera used. The product of the F number of the camera lens and the distance from the flash light source to the subject is a constant. Following the inverse square law, in order to obtain the same proper exposure on the film or image sensor, the F number is the relative illumination of the subject. The square root of. This constant is named "Flash Guide Number" and is a very useful index for flash photographers because the flash guide number is In a sense, it indicates the lighting power of a light source. Whether it is a flash unit with or without an integral reflector or an electronic flash unit, by The F number of the camera lens can be easily set by dividing the light index by the distance from the flash light source to the subject. Determination of the guide number of electronic flash devices for photography

1 Scope

This document defines the terms and definitions of the guide number of electronic flash devices and determines the calculation formula and expression method of the guide number. This document does not contain the definition and description of the measurement methods for the light output of electronic flash devices as defined in ISO 2827. This document applies to the measurement of the guide number of electronic flash devices used in photography.

2 Normative references

This document has no normative references.

3 Terms and Definitions

The following terms and definitions apply to this document. 3.1 Flash index guide number; GN NGN Related to the ISO sensitivity of the film or digital camera used, the camera's required sensitivity to obtain the proper exposure for the film or image sensor. The product of the lens aperture (F-number) and the distance from the flash light source to the subject. Note. The unit is meter (m). Appendix A provides the conversion calculations for converting meters to feet. 3.2 ISO flash index ISO guide number For film or digital cameras with a sensitivity of ISO 100, the "X" sync and the corresponding exposure time can fully absorb the flash The total output of the light source.

4 Guide Number Calculation Formula

4.1 ISO Guide Number The ISO flash index NISO /GN should be calculated according to formula (1). NISO /GN= k∫I(t)dt (1) Where. k ---value is 0.511m-1×m2·s-1; ∫I(t)dt ---Integral of the luminous intensity of an electronic flash device over time, in candela seconds [cd·s (cd·s=lm· sr-1·s)]. The explanation of formula (1) is given in Appendix B. 4.2 Guide Numbers other than ISO 100 For ISO values other than 100, the guide number can be calculated using formula (2).

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