- Types of Brightness. Two types of Diffuse brightness are commonly discussed, and a standard exists for both of them. ISO C Brightness (ISO 2470-1, TAPPI 525) uses Illuminant C level of UV energy. It was selected as the best approximation of normal office lighting conditions. ISO D65 Brightness uses Illuminant D65 (daylight).
- Mar 19, 2014 The TAPPI standard (GE brightness) measures the ability of a paper to reflect blue light. On a scale of 0 to 100, the higher the number, the brighter the sheet.
- The CIELAB color scale is another uniform color scale recommended by the CIE in 1976 to improve on the 1966 version of the Hunter L, a, b. It is in wide spread use today in many industries. As with HunterLab, this color scale can be used to determine color.
This brightness measurement is most common in the United States, and is the one described in TAPPI T 452 'Brightness of Pulp, Paper, and Paperboard (Directional Reflectance at 457 nm).' In Canada, Europe, and South America, Elrepho or ISO brightness is more commonly used.
Previously we covered Paper Specifications-Brightness and how brightness can affect the printed color when printing with inkjet. Paper Whiteness can also have an affect on the printed color value and it’s important to understand the distinction between whiteness and brightness.
While paper brightness and whiteness are somewhat similar, they are not interchangeable.
Refresher… a paper’s Brightness measure is the amount of reflectance of a specific wavelength of blue light. Brightness is generally measured on a scale of 0 to 100 – the higher the number, the brighter the paper. Because of capturing only the blue light, papers which measure brighter can often visually look the same as lower measured papers. There are also multiple “standards” for measuring brightness so make sure you are comparing measures from the same system (TAPPI, ISO, D65).
Whiteness measures the reflection of all wavelengths of light across the visible spectrum. By capturing the entire spectrum, the whiteness measure is better aligned with our visual perception.
So, the higher the measured whiteness rating (which also uses a 0-100 scale with exceptions noted below), the whiter the paper will appear.
Using the entire spectrum of visible light, paper with a very high whiteness number can appear to have a blue tint depending on what light source it is viewed under. Remember, unlike brightness, we are capturing all the wave lengths of the paper including blue.
Think of the hue or color a light bulb gives off.
When a measurement is above 100, it indicates that the paper contains Optical Brighteners, called OBA’s. These OBA’s will give paper a blue tint.
OBA’s are chemical compounds that absorb light in the ultraviolet and violet region (usually 340-370 nm) of the electromagnetic spectrum, and re-emit light in the blue region (typically 420-470 nm) by fluorescence. These additives are often used to enhance the color appearance of paper with the intention of giving it a visual blue-white shade.
The most common whiteness measure, D65 illumination, represents outdoor daylight. This standard is called CIE Whiteness and was developed by the French-based International Commission on Illumination (also abbreviated CIE). Indoor lighting, of course, will change how white the paper appears, and this will vary even more between fluorescent and incandescent bulbs.
A warm white shade will absorb the blues and cooler colors.
A blue white shade will absorb the warmer colors and reflect more blues or cooler colors.
When color profiling using L*A*B* measures, mid-tones and shadows are adjusted to the amount of blue found in the B* value of the paper. But for high light areas which allow more paper to show through and have little to no cyan found, blue cannot be adjusted and therefore highlight and flesh tones can can take on a visual blue tint. This is not an issue with the ink itself, but from lack of dot fill causing more paper showing through. Papers high in OBA’s can cause issues when color matching with inkjet.
Paper whiteness is particularly important in markets for which small text and readability is important such as book as well as magazine. For magazine images, the level of OBA’s in the paper can affect color reproduction accuracy of certain colors combinations.
Remember to test your images through fingerprinting the ink, machine and paper to assure that any OBA’s in your paper do not affect your high light and flesh tone areas.
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| ALL ABOUT PAPER BRIGHTNESS |
| The terms 'brightness' and 'whiteness' are often used interchangeably when considering paper. While for the regular layperson this crossover may not be detrimental, it is an important differentiation for those involved in the printing and art realms. Brightness is the measure of the amount of blue light reflected off a sheet of paper. Essentially the volume of light. Whiteness is the measure of the amount of all light reflected off a sheet of paper. Essentially the quality of light. This article will deal with paper brightness; what it is, how it is determined, and how it affects print quality. To read more, see our All About Whiteness article. |
SUMMARY
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| WHAT IS BRIGHTNESS? |
| When measuring brightness, a light source is directed at the paper in question, and the amount of blue light reflected off the surface is recorded. The wavelength for blue light is 457 nanometers. The type of light source varies depending on the testing method used. These methods are discussed in the next section. Brightness measurements were first developed to test the results of bleaching wood pulp. The bleach removes the natural yellowish tint of the natural pulp, and the test would be able to determine the change before and after the process. Today, most papers - at least for printing - are bleached to some extent. The measurement is based on the percentage of light reflected back, based on a scale between 1 and 100%. The higher the percentage, the more blue light reflected by the paper, and the brighter it appears. Just because two different papers have the same brightness rating, however, does not mean they will appear the same color to the human eye. Since only one wavelength (color) of light is measured, brightness does not account for the amount of other wavelengths reflected off a paper. Two papers could reflect 87% of the blue wavelength, while one reflects 50% and the other reflects 80% of the red wavelength. OBAs In general, white papers have a brightness of between 60 and 90%. However, added optical brightening agents (OBAs) can raise this number considerably. This is why you may have come across a paper with a brightness above 100. This is not possible in a natural situation, where the paper is constructed solely of wood pulp. Once brighteners are added, however, UV light is reflected in addition to the other wavelengths. The UV light going to the paper is not visible to the human eye, but the brighteners transform it into visible light. Therefore, more visible light is reflected off the paper than was absorbed onto it, making it appear brighter. Since brightening agents haven't been around for too long, their stability and archival reliability is still uncertain. It is known they may fade over time, diminishing the perceived brightness of the paper. In addition to the percentage rating, brightness may also be identified by a name such as Ultra Bright or Very Bright. These 'ratings' are not standardized, however, and should not be used to compare papers. | Brightness is a paper specification
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| PAPER BRIGHTNESS STANDARD TESTS |
Iso Brightness Vs Tappi Brightness
Brightness is generally measured using one of three different tests. Unfortunately, these tests use such different criteria, it is difficult to reliably compare a paper with one test's rating to a paper with a different test's rating. TAPPI Brightness Test
ISO Brightness Test
D65 Brightness Test
Test Comparison
| TAPPI Brightness Test |
| HOW BRIGHTNESS AFFECTS THE PRINT |
Knowing the brightness of a sheet of printer paper doesn't do you much good if you don't know how that brightness will affect your printed image. These are some general guidelines, though external conditions will affect any print, so these are not hard and fast rules.
| Left to right: Photo Rag; German Etching; Enhanced Matte |
Tappi Versus Iso Brightness Scale 2016
| At KeenART Media, we use a variety of different fine art and photographic papers. Visit our Fine Art Prints page to see the full list of papers we offer, and the Brightness rating for each paper. If you have questions about any of our fine art paper prints, or any of our other services or products, don't hesitate to contact us. Our knowledgeable staff is always happy to assist with answers, advice, or suggestions. |