GB/T 42999-2023Home textiles - Determination of the light blocking effect of fabric - Illuminometer method (English PDF)

Foreword

This document was issued on 7 September 2023 by the State Administration for Market Regulation; Standardization Administration of the PRC and takes effect on 1 April 2024.

It is a GB/T standard: recommended rather than compulsory, but it is the text a Chinese reviewer applies when assessing a submission.

1 Scope

GB/T 42999-2023 covers how much light a home textile fabric blocks, measured with an illuminometer rather than judged by eye, and applies to home textile fabrics and the products made from them. The principle is a ratio: light of a stable intensity is shone on the surface of the sample, the illuminance is measured after the light has passed through it, and that reading is compared with the illuminance measured with no sample in place, the comparison being what characterises the light blocking effect. The apparatus is described inside the test method clause — a test chamber that holds the sample, with a round hole in the centre of its top, and a light source that simulates sunlight — and the definition of light blocking effect itself sits in the terms clause, since it is the quantity the whole document turns on. Scope, normative references, terms, principle, test method and test report is the entire structure. Fixing the chamber geometry and the light source so tightly is what makes the figure transferable: a light blocking claim is a selling point as much as a technical property, and two mills quoting different numbers for the same cloth is a dispute nobody settles without a shared method. Fabric mills, home textile brands and testing laboratories are the readers.

This document describes the test method for determination of the light blocking effect

to fabric using an illuminometer.

This document applies to home textile fabrics and their products.

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.

GB/T 6529 Textiles - Standard atmospheres for conditioning and testing

3 Terms and definitions

For the purpose of this document, the following terms and definitions apply.

3.1

light blocking effect

The ability of textiles to prevent the transmission of light.

NOTE: It is expressed as blocking rate.

3.2

illuminance

The quotient of the luminous flux incident on the surface element containing the point

divided by the area of the surface element.

NOTE: The unit is lux (lx).

[Source: GB 50034-2013, 2.0.6, modified]

4 Principle

Irradiate stable light with a certain intensity on the surface of the sample, measure the

illuminance after the light passes through the sample, compare it with the illuminance

without the sample, and characterize the light blocking effect of the fabric by

calculating the light blocking rate of the sample.

5 Test method

5.1 Test apparatus

5.1.1 The light blocking effect test apparatus shall include: a test chamber for placing

the sample, with a round hole in the center of the top; a light source simulating sunlight

is placed directly above the test chamber and vertically corresponding to the round hole

of the test chamber; an illuminometer is placed at the bottom of the test chamber to

measure changes in illuminance. Figure 1 shows a schematic diagram of a light

blocking effect test apparatus. Other apparatuses with the same effect can also be used.

5.1.2 Test chamber: The size is approximately 40 cm x 40 cm x 10 cm. The diameter

of the round hole at the top that exposes the sample to the light source shall be 10 cm.

The internal surface of the test chamber shall be covered with black coating material to

avoid light reflection inside the chamber that will affect the test results.

5.1.3 Light source: Halogen lamp, the illuminance can reach up to 199000 lx, installed

on a height-adjustable shelf.

5.1.4 Illuminometer: It shall be located at the center position below the round hole of

the test chamber. The test range is 0.01 lx ~ 199000 lx. The measurement accuracy of

the illuminometer is +/-2 %.

5.4 Test procedures

5.4.1 Turn on the power switch of the test apparatus and the power indicator light will

light up.

5.4.2 Calibrate the illuminometer.

5.4.3 Set the illuminance of the light source. Set the illuminance of the light source of

the apparatus to 100000 lx, and read the illuminance value (i0) in this state.

5.4.4 Measure the illuminance value of the sample. Place the sample on the upper part

of the apparatus, with the test surface facing the light source, the surface of the sample

is flat and wrinkle-free, and read the illuminance value (i1) passing through the sample.

5.5 Result calculation

5.5.1 Calculate the blocking rate (%) according to formula (1). The test result is the

average of three samples, rounded to single digits.

where:

T - the blocking rate, %;

i1 - the illuminance value after installing the sample, in lux (lx);

i0 - the illuminance value when the sample is not installed, in lux (lx).

5.5.2 For homogeneous samples, use the average of three samples as the test result; for

samples with different colors or fabric structures, report the average of the test results

for each color or structure.

6 Test report

The test report shall include the following content:

a) Indicate that the test is conducted in accordance with this document;

b) Description of the sample;

c) Test temperature and relative humidity;

d) If necessary, indicate the test surface of the sample;

e) Test results;

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