Spectrophotometer for Paper Color Measurement

What is the Spectrophotometer for Paper Color Measurement?

A spectrophotometer measures paper colour across the visible spectrum and converts the data into CIE colour coordinates, whiteness and yellowness under standard illuminants. It is used for shade control, print colour matching and shade tolerance verification.

Overview

The instrument measures reflectance at wavelengths across the visible range, typically from 360 to 750 nm in 10 nm steps, using either diffuse illumination with 8 degree viewing, excluding the specular component, or the 45 degree illumination and 0 degree viewing geometry used in printing. From the spectral data the software computes tristimulus values and colour coordinates for stored illuminant and observer combinations, together with whiteness, yellowness, tint and colour differences against a target. A paper laboratory serving printing needs both: the diffuse geometry follows the paper standards for opacity and related values, while the 45 degree geometry approximates the appearance of printed surfaces and correlates with visual colour judgement. Calibration uses a certified white tile and black trap, and coloured tiles where wavelength verification is required.

How does it work?

A brightness or reflectance instrument illuminates the specimen diffusely and measures the light reflected at right angles, using a defined geometry, illuminant and observer so that results are reproducible between laboratories. ISO brightness is the diffuse blue reflectance factor measured with an effective wavelength of 457 nm under illuminant C, and it is highly sensitive to fluorescent whitening agents. Whiteness is a single number derived from the full colour coordinates under illuminant D65 or C, while yellowness, tint and shade are obtained from the same measurement. Opacity is the ratio of reflectance of a stack-backed specimen to that of an infinite stack, and can be determined by diffuse reflectance or by the contrast ratio of luminous reflectance. Gloss is measured separately at a fixed angle of incidence, because it depends on surface finish rather than on bulk optical properties.

What are the key features?

• Spectral measurement from 360 to 750 nm
• Diffuse 8° and 45°/0° geometries
• Colour coordinates for several illuminants and observers
• Whiteness and yellowness computation
• Colour difference against stored targets
• Certified tile calibration and wavelength check

What are the technical specifications?

A typical spectrophotometer for paper color measurement configuration offers spectral range of 360–750 nm at 10 nm intervals, geometries of Diffuse/8° and 45°/0°, wavelength accuracy of ±0.5 nm, repeatability of Colour difference below 0.05, inter-instrument agreement of Colour difference below 0.2 typical and illuminants of A, C, D50, D65 and others. Values are indicative of the product class; the exact figures for each configuration are confirmed on the quotation and the calibration documents supplied with the instrument.

Which applications is it used for?

The Spectrophotometer for Paper Color Measurement is used in shade control of tinted and coated papers, colour difference verification against a target, print colour matching and proof comparison and research on dyes and fluorescent whitening agents. Across the wider Brightness Testing class, laboratories also deploy it for brightness verification of printing and writing papers, whiteness and shade control for coated papers and opacity checks for lightweight printing grades.

Which standards and certifications apply?

Relevant standards and methods include ISO 2470-1, ISO 2470-2, ISO 2471, ISO 11475, ISO 11476, ISO 5631-1, TAPPI T452, TAPPI T525 and IEC 61010-1. Certification candidates for this model are CE and ISO 9001 manufacturing; each is to be confirmed for the specific configuration before shipment, and certificates are supplied only where they have been issued.

Keep the instrument calibrated with certified standards traceable to a national laboratory, and check the white standard and black trap at the start of each measurement series. Stack at least the number of sheets the method requires behind the specimen to ensure an opaque backing, because too few sheets allow the backing plate to influence the reading. Condition specimens to the standard atmosphere and protect them from light and heat, since fluorescent whitening agents bleach and papers yellow on exposure. Clean the measuring aperture and the standard regularly, avoid touching the measurement area of the specimen with fingers, and record the geometry, illuminant and observer with every result.

How do I select the right Spectrophotometer for Paper Color Measurement?

Specify a spectrophotometer when the specification involves colour coordinates, shade tolerances or print matching rather than a single brightness value. Confirm which geometries, illuminants and observer combinations are needed, and check inter-instrument agreement if several sites must report comparable numbers.

How does it compare with other Brightness Testing variants?

Match the instrument to the parameter named in the product standard. ISO brightness requires a 457 nm effective wavelength with the specified geometry, while D65 whiteness, colour and yellowness require a spectrophotometer covering the visible range under standard illuminants and observers. Opacity is measured with either a dedicated contrast ratio instrument or a spectrophotometer able to compute it from reflectance data. Gloss needs a dedicated meter with the correct incidence angle for the paper grade. Where the laboratory also verifies print appearance or matches shades, a benchtop spectrophotometer with both measurement geometries and a full set of illuminant and observer combinations is more useful than a single purpose meter, even though it costs more.