Spectrophotometer and colorimeter for car paint: how they work, when to use them and what the difference is

Why these tools exist: the limits of the color code

The color code describes the original paint, not the current one

A car's color code identifies the paint formula applied at the factory, on the vehicle's production day. It is a reference to a moment in time — not to what is found on the bodywork today. In the vast majority of cases this is enough: the code allows you to order a formula that, applied with the correct technique, comes very close to the original shade, and blending at the edges of the touch-up completes the job.

But there are situations in which this path does not work. The first is uneven fading: areas of the bodywork directly exposed to the sun (hood, roof) can fade in a visibly different way compared to more protected areas (pillars, lower sections), making it impossible to find a single formula that matches the whole vehicle. The second is a previous repaint: if the car has already been repainted in the past, the current color may not match the original OEM code at all — it may be a different shade, a non-standard variant, or a handcrafted formula from the previous body shop, or a repaint done with generic products not specific to bodywork or to that model. The third is a classic car or a car from a brand no longer active: official databases for these vehicles are often incomplete or simply no longer accessible through ordinary channels; only some specialized databases cover these cases, such as VerniciSpray's, which for several brands goes back to the 1960s and beyond. The fourth is a custom color: special paint jobs, bespoke shades (custom colors created specifically for a client), or modifications made after the original do not exist in any database. In all these scenarios, the only way to find the correct color is to measure it directly on the bodywork.

How a spectrophotometer works: physics explained simply

Color is reflected light: start from physics to understand the tool

To understand how a spectrophotometer works, you need to start from a fundamental truth: colors do not exist in objects. They exist in light. When sunlight hits a red body panel, the pigments in the paint absorb most of the wavelengths in the visible spectrum — green, blue, yellow — and mainly reflect those in the red range. That reflected light reaches the eye and is interpreted as "red." Change the composition of the incident light, and the perceived color changes: this is why a car seen in the sun looks different from the same car seen under the neon lights of a workshop.

The spectrophotometer exploits exactly this principle, but in a controlled and quantitative way. It internally emits a standardized white light source — which contains all visible wavelengths, from about 400 nm (violet) to 700 nm (red) — and projects it onto the surface being analyzed. The reflected light is collected and passed through an optical system (a prism or a diffraction grating) that splits it into individual wavelengths, exactly like a glass prism splits sunlight into a rainbow. At this point, photodetectors measure how much light is reflected at each wavelength, producing a spectral reflectance curve: a graph that shows, at each point in the visible spectrum, the percentage of light reflected by the surface.

This curve is the unique digital signature of the color. No paint in the world produces exactly the same reflectance curve: it is like the fingerprint of that specific paint, in that specific state of aging, on that specific surface. A normal spectrophotometer measures reflectance across 31 wavelength intervals, each 10 nm wide. More advanced models reach over 150 measurement points over a wider window.

From the curve to the formula: the role of the database

The reflectance curve alone does not produce the paint formula. It is a measuring tool, not a mixing tool. The next step takes place in the software connected to the instrument: the colorimetric algorithm compares the curve measured on the bodywork with the reflectance curves of thousands of formulas in the paint manufacturer's database. The software identifies the formulas whose reflectance profiles are most similar to the measured one, orders them by similarity, and suggests them to the body shop as candidates to evaluate with a color test.

The databases of the main paint manufacturers (Axalta, PPG, AkzoNobel, BASF, Sherwin-Williams) contain hundreds of thousands — in some cases millions — of color formulas, constantly updated with new OEM shades. However, in body repair, the simple availability of a large number of formulas is not enough: to achieve a reliable match it is essential to refer to specialized automotive databases, designed to handle variants, production cycles, and paint aging.

For this reason, when choosing paint it is important to evaluate not only the final product, but also the color system it is based on and the databases used by the supplier. Transparency on these aspects is a concrete indicator of reliability. In particular, the best results are obtained when the supplier refers to specialized automotive databases and to search and optimization tools updated for real body shop use. An example in this direction is VerniciSpray, which uses Palini Colori as its main supplier, a company with a database of over 900,000 formulas specific to the automotive sector and constantly updated proprietary systems.

How a colorimeter works: the simpler tool

The colorimeter imitates the human eye

The colorimeter is a different instrument from the spectrophotometer, even though the two terms are often used interchangeably — even by retailers and e-commerce sites, with a certain technical imprecision that is worth clarifying.

While the spectrophotometer measures surface reflectance across dozens of distinct wavelengths, the colorimeter uses only three colored filters — red, green, and blue, corresponding to the three types of cones in the human retina — to estimate the eye's visual response to that color. In practice, it imitates the way the eye perceives color, translating it into numerical values in the CIE L* a* b* color space: L* indicates lightness, a* the position on the green–red axis, b* the one on the blue–yellow axis. These three values are often accompanied by Delta E (ΔE), which expresses the total color difference between two samples numerically.

This approach has concrete advantages: colorimeters are cheaper, more compact, faster, and simpler to use than spectrophotometers. They provide a concise and immediate reading of the color difference between two surfaces, without requiring complex software or database connections. For repetitive quality control in production — verifying that two panels made in the same plant have the same color within a defined tolerance — the colorimeter is often the most practical tool.

The limits of the colorimeter: metamerism and information loss

The fundamental limitation of the colorimeter emerges in a situation known to color professionals as metamerism. Metamerism is the phenomenon whereby two surfaces with different pigment formulas may appear identical under one light source (for example natural daylight) and clearly different under another source (for example a halogen or LED lamp). This happens because the two surfaces, while producing the same response in the three RGB channels of the eye under a certain light condition, have different reflectance curves that behave differently as the spectrum of incident light changes.

A colorimeter, using only three values, is not able to detect metamerism: two metameric colors look identical to the instrument even though in reality they will visibly diverge when the light changes. The spectrophotometer, by measuring the entire reflectance curve, can detect and signal it. In the context of body repair touch-up, this difference is significant: a repainted panel that looks perfectly matched in the artificially lit workshop may show an obvious mismatch in sunlight, and the colorimeter cannot predict this problem.

Real differences between spectrophotometer and colorimeter: which one should you choose?

The technical and practical comparison

The distinction between the two tools is not simply one of price or abstract precision: it is a difference in the type of information produced, which determines what can and cannot be done with each instrument. The following table summarizes the main differences in the two dimensions that matter most in a body repair context: technical capability and practical use.

An important clarification: ambiguous terminology in the market

In the consumer market and online sales channels, the terms "colorimeter" and "spectrophotometer" are often used interchangeably or incorrectly. Many inexpensive portable devices describe themselves as "spectrophotometers" while technically being colorimeters: they measure three color channels rather than the entire spectral curve, and they are not able to communicate with the professional databases of body paint manufacturers. For amateur home use (matching the color of a wall, checking the shade of a fabric) they can be useful tools. For professional body repair touch-up — especially on metallics, pearlescents, classic cars, or repainted vehicles — a 3-filter colorimeter is not a substitute for the spectrophotometer: it is a different tool, with different capabilities.

The multi-angle spectrophotometer: the solution for metallic and pearlescent finishes

Why a single angle is not enough for effect colors

Standard spectrophotometers for general building and industrial applications measure reflectance from a single fixed angle (typically 45°). On solid colors — pastel, white, black — this is sufficient: the reflectance curve is stable and does not vary significantly as the angle changes. But on metallic and pearlescent colors, a single measurement angle is deeply insufficient, for a precise physical reason.

Metallic colors contain microscopic aluminum flakes suspended in the paint. These flakes behave like tiny mirrors: they direct light in a directional way, and the amount of light reflected toward the eye changes radically depending on the viewing angle. A silver metallic seen head-on (90° relative to the surface) may look almost white; the same color seen from the side at 20° may look dark gray. This phenomenon is called flop, and it is an intrinsic characteristic of all effect colors. Pearlescent and mica-based finishes, based on coated mica pigments, show an even more complex behavior: they change both brightness and hue as the angle of light changes, giving rise to iridescent effects.

A single-angle spectrophotometer measures only a "photograph" of the color — the frontal one — losing all information about angular variation. The result is that two metallic colors with the same frontal appearance but with flakes of different size, density, or orientation look identical to the instrument, while to the eye they are clearly different from oblique angles. For this reason, touch-up of metallics and pearlescents with only single-angle data often leads to matches that look perfect in the workshop but show an obvious difference in sunlight.

How multi-angle works: more angles, more information

Multi-angle spectrophotometers — the true professional standard in body paint work — measure reflectance simultaneously from multiple angles, typically five: 15°, 25°, 45°, 75°, and 110° relative to the surface normal. More advanced models add a sixth negative angle (-15° or similar) specific to measuring the grain of coarse metallics (the so-called sparkle) and interference pigments such as chameleon finishes. Each angle captures a different "slice" of the paint's optical behavior: head-on brightness, flop, grain effect, color shift.

Multi-angle spectrophotometers are the true professional standard in the body paint sector, used to detect color objectively and repeatably. Specialized companies such as X-Rite, Konica Minolta, or BYK-Gardner develop devices designed to work on complex surfaces and effect finishes. These tools are then integrated into the color systems used in the automotive sector, where software and databases come into play for processing and formula search, as also happens in systems adopted by companies such as Palini Colori. From a technical point of view, the instruments are equipped with an autonomous light source, allow measurements independent of ambient conditions, and transmit data to the software connected to the instrument. In practice, however, the spectrophotometer is not used in isolation, but within a workflow that includes data interpretation and formula selection. For this reason, its effectiveness is closely linked to the color system with which it is used.

When to use the spectrophotometer: classic cars, repaints, and unknown colors

Classic cars and brands no longer active: no database is complete

Restoring a classic car presents a unique colorimetric challenge: OEM databases for old brands may no longer be maintained in the information systems of current paint manufacturers. Even when the original color code is known and readable on the plate, the corresponding formula may not be present in the database, or there may only be a generic variant.

In this scenario, the spectrophotometer becomes the mandatory starting tool. The correct sequence is: find an original section of the bodywork in good condition (preferably protected from direct exposure, such as an area under a molding or inside a compartment), polish that area until the surface oxidation layer is removed and the paint regains its original gloss, then perform the spectral reading. The software searches the database for the formula most similar to the measured curve and proposes it as a starting point for mixing. The result is not necessarily a perfect match at the first attempt, especially on historical colors from the 1960s–1980s, but it remains the most rational and verifiable method available.

It must always be kept in mind that many original shades were based on pigments that are now eliminated or replaced because they contained heavy metals such as lead (lead chromates), cadmium, and hexavalent chromium compounds. These substances have been progressively abandoned due to health risks (CMR classification) and environmental impact, as well as because of European regulations, in particular the REACH Regulation (EC 1907/2006, Annex XVII and SVHC list) and the CLP Regulation (EC 1272/2008), which limit or ban their use in paint products.

Repainted vehicles, fading, and out-of-catalog colors: when the OEM code is not enough

When a vehicle has been repainted, the OEM code identifies only the original factory color and not the one actually present on the bodywork, making any order based on that data inherently wrong; the spectrophotometer instead measures the actual color and, through the reflectance curve, identifies a match in the database or proposes the closest formula even in the case of custom mixes, providing an objective, data-driven starting point. This approach becomes especially relevant on very old vehicles, where years of UV exposure may have caused uneven fading between panels with different exposure; therefore, this is not a dynamic typical of recent vehicles. In many cases, before resorting to instrumental analysis, it is possible to obtain a visually acceptable result through professional painting techniques such as blending, which allows the new color to be integrated with the existing one, reducing perceived differences. Only when these techniques are not sufficient to compensate for chromatic variations — and the risk of discontinuity remains high — does it make sense to apply panel matching with a spectrophotometer, measuring the adjacent panel to replicate its actual state with a level of precision that cannot be achieved by eye alone. Finally, in cases of bespoke or out-of-catalog colors (including OEM customizations), where no standard reference exists, the spectrophotometer remains the only tool capable of capturing the color signature and guiding a credible formulation, leaving the painter only the fine adjustment on an objective basis rather than on assumptions.

Practical use of the spectrophotometer: what you really need to know

In practice, the reliability of the reading depends more on surface preparation than on the instrument itself: dirt, waxes, or oxidation of the clear coat alter reflectance and lead to inaccurate data, which is why thorough cleaning, degreasing, and a light polish are recommended steps before measurement. Method also matters: the instrument must be placed correctly and the readings repeated to verify consistency, especially on metallic or pearlescent colors where orientation affects the result. Once the data have been acquired, the software proposes compatible formulas based on Delta E, but these are only a starting point: final validation always takes place through a color test.

Frequently asked questions about spectrophotometers and colorimeters in body repair

These questions gather the most common doubts that arise when first approaching the topic of instrumental color measurement for body repair touch-up.