In heritage digitization, the performance of a book scanner is not limited to its resolution or the quality of its sensor. One fundamental element determines the fidelity of the images produced: lighting.
Lighting is what reveals the colors, textures, and nuances of the documents being digitized. Inadequate lighting can degrade the quality of a scan, even when using very high-end professional equipment.
Why lighting is a determining criterion
During digitization, the sensor does not capture the colors of the document directly, but rather the light that is reflected, emitted, or diffused by it. The quality of the lighting used is therefore decisive: it directly influences color reproduction, detail readability, and the consistency of the resulting images.
In the heritage context, where visual accuracy is essential for the preservation, analysis, and dissemination of works, lighting must be considered a core component of the scanner.
Lighting and color rendering: a reference to natural light
Color rendering is one of the fundamental criteria for evaluating the quality of artificial lighting. It refers to a light source’s ability to faithfully reproduce the colors of an object, in comparison with a natural reference: daylight.
Unlike sunlight, which contains all wavelengths of the visible spectrum, artificial light sources often have an incomplete spectrum. Certain chromatic components may be missing or underrepresented, leading to altered color perception.
In the digitization of books and heritage documents, this difference is critical: inadequate lighting can alter the appearance of inks, pigments, and paper substrates at the very moment of capture.
What is expected from lighting in heritage digitization
A lighting system designed for heritage digitization must meet several requirements simultaneously:
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Colorimetric accuracy, to respect the tones of the original document;
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Perfect uniformity, to avoid variations and artifacts;
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Stability over time, ensuring project reproducibility;
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Absence of UV and IR radiation, which are harmful to fragile historical documents.
These constraints explain why lighting is often one of the most complex elements to design in a professional book scanner.
Light spectrum, color reproduction, and the role of the CRI (Color Rendering Index)
White light is composed of all visible colors, from violet to red. A high-quality lighting system must reproduce them in a balanced and continuous way to accurately reveal all the colors of a document.
If a light source lacks necessary color components and therefore has an incomplete spectrum—as is often the case with low-quality artificial lighting—color reproduction becomes partial.
For example, an old red pigment or a brown ink may appear dull or inaccurate if warm tones are poorly rendered, while the paper may look overly gray or yellowish.
This phenomenon is precisely what the CRI is designed to quantify.
Focus on CRI: an indicator of light spectrum fidelity
The CRI measures the ability of an artificial light source to faithfully reproduce colors compared to a natural reference source with the same color temperature.
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A CRI of 100 corresponds to ideal color rendering, equivalent to sunlight;
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The higher the CRI, the more natural and balanced the colors appear;
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A low CRI indicates an uneven light spectrum and distorted color perception.
In book scanners, manufacturers aim to get as close as possible to this reference value, even though absolute perfection remains theoretical.
CRI, color temperature, and stability: a holistic approach
CRI cannot be interpreted in isolation. A high value only makes sense when combined with:
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An appropriate and constant color temperature (generally around 4000 to 5000 K),
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Long-term stability of the light spectrum,
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Homogeneous illumination across the entire surface of the document.
This combination is what ensures faithful and reproducible digitization results.
Why aim for a CRI above 95 in book scanners?
Book scanners dedicated to heritage digitization now use high-CRI LED light sources, capable of reaching values above 90–95.
These systems make it possible to closely replicate the behavior of natural light, while providing the stability, safety, and reproducibility that are essential for heritage preservation.
Conclusion
In heritage digitization, lighting is not a detail—it is the key to accurate color reproduction and clear detail visibility. High-quality lighting, with a complete and uniform spectrum and a high CRI, helps minimize errors and reproduce works as they truly are. Choosing a scanner equipped with high-performance lighting means ensuring that every digital image remains a faithful and lasting representation of cultural heritage.