Determination of the Brightness Coefficient of Exercise Books: Standards, Test Methods, and Complian

The brightness coefficient (blue reflectance factor) of exercise books is a key optical safety index for student stationery, because excessively white paper—often caused by overloading with fluorescent whitening agents—can aggravate visual fatigue and is strictly limited by mandatory standards. Determination is performed with reflectance photometry in accordance with GB 21027, GB/T 7974, and ISO 2470, which cap the brightness of paper used in workbooks at 85%. This article explains the principle, sample types, instrumentation, measurement procedure, and typical applications of exercise book brightness coefficient determination.

Technical Overview

The brightness of an exercise book—often described in everyday language as whiteness—is quantified as the diffuse blue reflectance factor, conventionally designated R457 or ISO brightness. It is defined as the reflectance of paper to light of an effective wavelength of 457 nm under standardized illumination and viewing geometry, expressed as a percentage relative to a perfect reflecting diffuser. Because highly bleached or optically brightened paper scatters a large amount of short-wavelength light, brightness is treated in many jurisdictions as a health-related indicator for student supplies rather than a purely aesthetic property.

To make workbook paper appear whiter, manufacturers commonly add fluorescent whitening agents (FWAs), also called optical brightening agents. These compounds absorb ultraviolet radiation and re-emit blue light, raising the measured blue reflectance factor. Over-bright pages increase glare and contrast stress during prolonged reading and writing, which is why the mandatory Chinese national standard GB 21027, General Requirements for the Safety of Student Supplies, limits the brightness of paper used in exercise books and workbooks to no more than 85%. Equivalent international determination methods are provided by ISO 2470-1, ISO 2470-2, GB/T 7974, and JIS P 8123.

• Brightness coefficient = blue reflectance factor at an effective wavelength of 457 nm
• Regulatory maximum for exercise book paper: 85% under GB 21027
• Values above the limit usually indicate excessive fluorescent whitening agent loading
• Measured with UV-calibrated diffuse reflectance photometers at accredited third-party laboratories or in-house quality facilities

Testing Samples

Finished Exercise Books and Workbooks

Complete commercial products, including stitched or glued exercise books, workbooks, composition books, and loose-leaf notebooks, are submitted in their final saleable state. Inner pages are sampled from multiple positions of each book to capture lot-to-lot and page-to-page variability. Testing of finished goods verifies that the product as placed on the market satisfies the brightness limit.

Base Paper and Paper Stock for Workbook Production

Paper mills and notebook converters submit jumbo rolls, cut sheets, or unprinted base stock prior to binding. Upstream testing shortens the feedback loop in production, allows fluorescent whitening agent dosing to be adjusted at the pulp, size press, or coating stage, and prevents nonconforming paper from being converted into finished goods.

Related Student Paper Stationery

Drawing books, sketch pads, loose-leaf filler paper, and other paper-based stationery intended for student use can be evaluated with the same procedure, particularly when the products are covered by procurement specifications, product certification schemes, or market surveillance programs.

Testing Items

The core determination is the blue reflectance factor; supporting measurements are frequently requested within the same test program:

• Brightness (blue reflectance factor, R457 / D65 brightness) determined in accordance with GB/T 7974 and ISO 2470-2, or ISO brightness under ISO 2470-1
• CIE whiteness (D65/10 or C/2 observer conditions) in accordance with ISO 11475 and GB/T 22879 for a fuller description of perceived whiteness
• Screening for fluorescent whitening agents by examination under an ultraviolet lamp at 365 nm as an interpretive aid
• Reporting of the arithmetic mean, standard deviation, illuminant, geometry, and calibration details

Testing Methods

Principle and Reference Standards

The specimen is illuminated diffusely inside an integrating sphere, and the reflected light is measured normal to the surface (d/0 geometry) through an optical channel with an effective wavelength of 457 nm and a spectral band half-width of approximately 44 nm. ISO 2470-1 defines ISO brightness under indoor daylight conditions (illuminant C), while ISO 2470-2 and GB/T 7974 define D65 brightness under outdoor daylight conditions. Both methods require ultraviolet-adjusted calibration so that the contribution of fluorescent whitening agents is captured reproducibly. GB 21027 uses the resulting value as the basis for the 85% compliance decision for exercise book paper.

Instrumentation

A reflectance photometer or spectrophotometer-based brightness tester equipped with an integrating sphere, a 457 nm filter or equivalent spectral channel, and a controlled ultraviolet source is used. Calibration is performed with a non-fluorescent working standard and, because fluorescent whitening agents respond to the UV content of the illumination, with a fluorescent reference standard traceable to a national metrology institute. Modern instruments automatically standardize the UV level to ensure interlaboratory agreement.

Specimen Preparation and Conditioning

Test pieces free of ink, watermarks, dirt, wrinkles, and surface contamination are cut from the workbook pages, typically at least ten specimens per sample, each larger than the measurement aperture. The specimens are conditioned to equilibrium in the standard atmosphere of 23 °C ± 1 °C and 50% ± 2% relative humidity in accordance with ISO 187. They are then stacked into an opaque pad so that the backing cannot influence the reading, and the test surfaces are never touched or folded. If the two sides of the paper differ appreciably, each side is designated and measured separately.

Measurement Procedure

• Verify and calibrate the instrument using both non-fluorescent and fluorescent reference standards.
• Place the conditioned opaque pad of specimens over the measurement port without contaminating the surface.
• Take readings on at least ten specimens or measurement spots, avoiding printed areas, margins, and edges.
• Record individual values and compute the arithmetic mean and standard deviation.
• Repeat the sequence for the reverse side where side differentiation is required.

Evaluation of Results

The arithmetic mean brightness value is compared with the 85% maximum specified in GB 21027 for the paper of exercise books. Values at or below the limit are considered conforming; values above 85% indicate excessive bleaching and/or excessive fluorescent whitening agent loading, and the product fails the safety requirement. The test report identifies the method applied, the illuminant, the geometry, the number of specimens, the mean, the standard deviation, and the UV calibration details.

Applications

• Mandatory compliance demonstration for student supplies placed on the market under GB 21027, including factory self-declaration and product certification support
• Incoming and in-process quality control at paper mills, converters, and notebook manufacturers, enabling fluorescent whitening agent dosage tuning and lot release
• Market surveillance and regulatory spot checks on stationery retailers, wholesalers, and e-commerce listings
• Screening by schools, education authorities, and centralized government procurement programs
• Export compliance and buyer specification verification where international contracts reference ISO brightness methods
• Technical documentation, safety files, root-cause analysis, and corrective action verification following nonconformities

FAQ

What is the brightness coefficient of an exercise book?

It is the blue reflectance factor (R457) of the workbook paper—its reflectance to light of 457 nm effective wavelength under standardized diffuse illumination—expressed as a percentage. It is the technical measure behind the everyday notion of paper whiteness.

What is the maximum permitted brightness for exercise books?

GB 21027 limits the brightness of paper used in exercise books and workbooks to no more than 85%. Paper brighter than this limit is regarded as a potential eyesight hazard for students and is judged nonconforming.

Why is high brightness treated as a safety issue?

Very high brightness is usually achieved with large amounts of fluorescent whitening agents, which increase the glare and blue-light component of the page and heighten the contrast stress between ink and paper, accelerating visual fatigue during long study sessions.

Which standards govern the determination?

GB/T 7974 and ISO 2470-2 specify D65 brightness, ISO 2470-1 specifies ISO brightness, and JIS P 8123 provides an equivalent method, while GB 21027 sets the 85% limit as part of student supply safety assessment. CIE whiteness may be additionally characterized under ISO 11475 and GB/T 22879.

How many specimens are measured and how are results reported?

At least ten conditioned specimens or measurement spots are tested on an opaque pad, and the arithmetic mean and standard deviation are reported together with the illuminant, geometry, and calibration information.

Where can the determination be performed?

Testing can be carried out in manufacturers' own laboratories for process control or, for regulatory compliance and dispute resolution, at accredited third-party laboratories competent in paper and stationery optical testing under an ISO/IEC 17025 quality framework.