Standard No.:	GB/T 2680-2021
English Name:	Glass in building—Determination of light transmittance, solar direct transmittance, total solar energy transmittance, ultraviolet transmittance and related glazing factors
Chinese Name:	建筑玻璃 可见光透射比、太阳光直接透射比、太阳能总透射比、紫外线透射比及有关窗玻璃参数的测定
Chinese Classification:	Q30    Ceramic and glass in general
Professional Classification:	GB    National Standard
Source Content Issued by:	SAMR; SAC
Issued on:	2021-03-09
Implemented on:	2021-10-1
Status:	valid
Superseding:	GB/T 2680-1994 Determination of light transmittance, solar direct transmittance, total solar energy transmittance and ultraviolet transmittance for glass in building and related glazing factors
Target Language:	English
File Format:	PDF
Word Count:	14500 words
Translation Price(USD):	435.0
Delivery:	via email in 1 business day

GB/T 2680-2021 Glass in building – Determination of light transmittance, solar direct transmittance, total solar energy transmittance, ultraviolet transmittance and related glazing factors 1 Scope This standard specifies the determination methods for the visible light transmittance, visible light reflectance, solar radiant flux, solar direct transmittance, solar direct reflectance, solar direct absorptance, total solar energy transmittance, secondary internal heat transfer factor, shading coefficient, visible light to total solar energy transmittance (LSG), ultraviolet transmittance, emissivity, and total solar infrared heat transmittance of glass in building, as well as related glazing factors. This standard is applicable to transparent materials such as single glazing and multiple glazing. 2 Normative references The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. ISO 10291 Glass in building - Determination of steady-state U values (thermal transmittance) of multiple glazing - Guarded hot plate method ISO 10292:1994 Glass in building - Calculation of steady-state U values (thermal transmittance) of multiple glazing ISO 10293 Glass in building - Determination of steady-state U values (thermal transmittance) of multiple glazing - Heat flow meter method 3 Terms and definitions For the purposes of this document, the following terms and definitions apply. 3.1 visible light transmittance τv ratio of the transmitted luminous flux to the incident luminous flux within the visible spectral range (380 nm to 780 nm), under CIE standard illuminant D65, with the CIE standard spectral luminous efficiency function as the weighting function 3.2 visible light reflectance ρv ratio of the reflected luminous flux to the incident luminous flux within the visible spectral range (380 nm to 780 nm), under CIE standard illuminant D65, with the CIE standard spectral luminous efficiency function as the weighting function 3.3 solar direct transmittance τe ratio of the radiant flux of solar radiation transmitted through the test object to the incident radiant flux in the wavelength range of 300 nm to 2,500 nm 3.4 solar direct reflectance ρe ratio of the radiant flux of solar radiation reflected by the test object to the incident radiant flux in the wavelength range of 300 nm to 2,500 nm 3.5 total solar energy transmittance g sum of the solar direct transmittance and the secondary internal heat transfer factor of the solar radiation absorbed by the glazing, also known as solar heat gain coefficient or solar factor 3.6 shading coefficient SC ratio of the total solar energy transmittance of the glazing to that of 3 mm-thick clear colorless glass under given conditions 3.7 total solar infrared heat transmittance gIR ratio of the sum of the solar radiation intensity directly transmitted through the glass and the portion of the solar energy absorbed by the glass and transmitted through secondary heat transfer, to the incident solar radiation intensity in the near-infrared band of the solar spectrum (from 780 nm to 2,500 nm) 3.8 visible light to total solar energy transmittance LSG ratio of visible light transmittance to total solar energy transmittance 4 Test conditions 4.1 Specimens 4.1.1 A single glazing may be used directly as the specimen, either by cutting a specimen from it or by using a piece of glass of the same material. 4.1.2 For a multiple glazing, the specimen may be prepared by cutting individual glass panes separately or by using pieces of individual glass panes of the same material. 4.1.3 The specimen shall be kept clean during determination. 4.2 Instruments 4.2.1 The measurement wavelength range and wavelength interval of the spectrophotometer, Fourier transform infrared spectrometer, and other instruments used for the determination shall meet the requirements for the wavelength range and wavelength interval of each parameter specified in this standard. 4.2.2 The instrument used for the determination shall be arranged so that, during measurement, the angle between the optical axis of the illuminating beam and the normal to the specimen surface does not exceed 10°, and the angle between any ray in the illuminating beam and the optical axis does not exceed 5°. 4.2.3 When determining a diffusing specimen or a specimen containing diffusing components, the instrument used for measuring transmittance and reflectance shall be equipped with an integrating sphere. 4.2.4 When determining the transmittance of the specimen, the transmitted light emerging from the specimen due to multiple reflections at the glass surfaces shall be included. 4.2.5 When determining the reflectance of the specimen, the reflected light emerging from the specimen due to multiple reflections at the glass surfaces shall be included. 4.2.6 The accuracy of the instrument for measuring transmittance and reflectance shall be within ±1%. 5 Determination of parameters 5.1 Visible light transmittance 5.1.1 Calculation method for visible light transmittance The visible light transmittance τv shall be calculated using Equation (1): (1) where, τv——the visible light transmittance of the specimen; λ——the wavelength; τ(λ)——the spectral transmittance of the specimen; Dλ——the relative spectral power distribution of the standard illuminant D65; V(λ)——the CIE standard spectral luminous efficiency function; Δλ——the wavelength interval; DλV(λ)Δλ——the product of the relative spectral power distribution Dλ of standard illuminant D65, the CIE standard spectral luminous efficiency function V(λ), and the wavelength interval Δλ; the values of DλV(λ)Δλ are given in Table 1.

Contents Foreword i 1 Scope 2 Normative references 3 Terms and definitions 4 Test conditions 4.1 Specimens 4.2 Instruments 5 Determination of parameters 5.1 Visible light transmittance 5.2 Visible light reflectance 5.3 Solar radiant flux 5.4 Solar direct transmittance 5.5 Solar direct reflectance 5.6 Solar direct absorptance 5.7 Total solar energy transmittance 5.8 Secondary internal heat transfer factor 5.9 Shading coefficient 5.10 Visible light to total solar energy transmittance 5.11 Ultraviolet transmittance 5.12 Emissivity 5.13 Total solar infrared heat transmittance 6 Test report Annex A (Normative) Thermal resistance calculation for glazing Bibliography