How to measure the color and brightness of a product?
The appearance of a product is one of the main reasons for buying by consumers, and is instinctively associated with its quality. All materials have the ability to reflect and absorb the energy and light they receive, which gives them a characteristic of tone and intensity of color and characteristic surface appearance (cleanliness, shine and mirror effect).
The first control must be visual, for which the fundamental tool is the light cabinet, which generates a controlled environment and allows the products to be seen under different illuminants or light sources.
Standard illuminants proposed by the CIE (International Commission on Illumination)
In order to establish standards for different types of lighting, the CIE defined a set of illuminants to allow the measurement and comparison of colors in different contexts. The most important are:
Illuminants A, B, and C were introduced in 1931, intended to represent average incandescent light, direct sunlight, and average daylight, respectively. Illuminants D represent the phases of daylight, Illuminant E is the illuminant of equal energy, while Illuminants F represent fluorescent lamps of different composition.
On the other hand, illuminants B and C are easily achieved with daylight simulations. They modify Illuminant A by using liquid filters. B served as the representative of the midday sunlight, while C represented the average daylight. Unfortunately, they are poor approximations of any phase of natural light. Once more realistic simulations were achieved, B & C illuminants were deprecated in favor of the D series.
Finally, the publication of an L series of illuminants is expected. It will represent various types of LED lighting.
| Name | Description |
| Iluminant A | It is based on the most common source of artificial light: the incandescent tungsten filament bulb. |
| IIuminants D | It consists of a series of four illuminants representing different daylight conditions (hence D, for daylight). They differ from each other by the equivalent color temperature, being called D50 (5003 K), D55 (5503 K), D65 (6504 K) and D75 (7504 K). Two of them, D50 and D65, are of great importance |
| Iluminants F* | They are a series of 12 illuminants designed to represent different types of fluorescent light, hence the name. They are classified into three groups: F1 to F6 (“standard” fluorescent types), F7 to F9 (full spectrum or wide band) and F10 to F12 (narrow band illuminants), to represent as many typical compositions of the different phosphors that are used in its construction. Of all of them, the most common are three: F2, F7 and F11, which are usually used as a reference to work with typical fluorescent lighting. F2: For use in warehouses and offices in the United States. Cool white fluorescent light. Color temperature 4,150 K. Also known by the acronym CWF (Cool White Fluorescent). It is the most representative illuminant of this group. F7: Daylight broadband fluorescent simulation (D65) in production monitoring industries F11: Describes the light from a fluorescent tube, used in offices and warehouses in Europe. Also described as TL84 and Ultralume 40, by their trademarks |
| luminant E: | A theoretical illuminant consisting of a perfectly uniform distribution (equal energy content for all wavelengths, hence E for equal) used as a reference for certain colorimetric calculations. Unlike the other illuminants, there are no natural or artificial sources with this spectral distribution. |
| UV: | Ultraviolet ligt |
| Horizon | Natural light that simulates horizon light, and does not correspond to any CIE illuminant |
* The TL84 and CWF light sources simulate the F11 and F2 illuminants (, respectively. The CIE F11 illuminant is the most widely used in environments in Europe and Asia. In turn, the F2 describes the standardized light of fluorescent tubes and lamps used more common in offices and usual work environments in the United States, which are usually described as “Cool White”, hence this type of lighting is also described with the acronym CWF.
| Iluminant | Description | Iluminant | Description |
| A | Incandescent / Tungsten | F1 | Fluorescent Daylight |
| D50 | Horizon Light. ICC profile PCS | F2 | Cool White Fluorescent |
| D55 | Mid-morning/ mid-afternoon | F3 | White Fluorescent |
| D65 | Noon daylight: TV, Srgb, color space | F4 | Fluorescent warm white |
| D75 | Northern Sky Daylight | F5 | Fluorescent Daylight |
| E | Equal energy | F6 | Lite fluorescent white |
| F7 | Simulator D65, daylight simulator | ||
| F8 | Simulador D50, Sylvania F40 Design 50 | ||
| F9 | Cool White Deluxe Fluorescent | ||
| F10 | Philips TL85, Ultralume 50 | ||
| F11 | Philips TL84, Ultralume 40 | ||
| F12 | Philips TL83, Ultralume 30 |
How to Select the Illuminant to use?
When choosing the illuminant to use when measuring or evaluating the color of a sample, consider its end use or where it will be sold. A fluorescent illuminant can be chosen if the product is sold in supermarkets or shopping centers, for example.
Standard Color Charts are used as standard quality control standards (internationally recognized) and for the objective communication of colors, shades and color deviations. On the other hand, it facilitates communication throughout the process: design, customer approval, supplier and raw material control, manufacturing, final product correction.
| Carta de color | Descripción |
| RAL | RAL color charts have been a global benchmark in the entire paint and coating industry since 1927. |
| Pantone | Pantone color charts are a world reference in the entire paint and coating industry |
| NCS | Natural Color System (NCS) is a logical color notation system that is based on how humans view color. It was developed by the Scandinavian Institute of Color in 1960 and is based on studies by Hering, who reduced all visible colors to the mixture of four unique shades: yellow, red, green and blue plus black and white. From the mixtures of colors with each other and with white and black that are increasing by 10% in intensity, 13 color scales are derived that have been considered an international standard since 1976. |
| Munsell | Munsell’s color ordering system is an accurate way of specifying and displaying relationships between colors. Each color has three qualities or attributes: hue, value, and chroma or saturation. He created numerical scales that tried to show the colors separated by visually equal spaces. |
Finally, the spectrophotometers measure the spectral curve, from which the Color Coordinates can be defined (ex. L * a * b *, L * c * h *, xyY) and establish tolerances in Color Difference (ex. dE *, dECMC, Metameria) between the defined color and the actual samples.
Sometimes we want to measure the brightness of a surface regardless of its color. In this case, we are not interested in the reflection in the internal layers of the material, but in the amount of incident light that is reflected specularly on the surface. Gloss is the main parameter to measure surface appearance. Depending on the gloss level of the sample, different measurement angles should be used (60º for all types of gloss; 20º for high gloss; 85º for low gloss). For this, instruments called gloss meters are used.
A glossmeter measures specular reflection. The intensity of reflected light is captured over a small margin of the angle of reflection.
The gloss measurement can be complemented with the measurement of other parameters such as the Veil (Haze) and the DOI that are becoming increasingly important, especially in shiny samples in which the sensation of cleanliness or a mirror effect is sought, since 2 samples with the same color and gloss may appear visually different if they have a different veil or DOI (orange peel).
| Parameter | Description |
| Velo/Haze | On high-quality surfaces, an image with a clear and bright appearance is expected. Microstructures cause a milky appearance. This effect is described as veil / haze and is frequently due to certain parameters of the production process, such as the type of resin, degree of dispersion or application process. The veil is characterized by measuring scattered diffuse light. |
| DOI | Mirror Effect or DOI is called the ability of a surface to perfectly reflect the light that falls on it. It is due to the lack of stretching of the product during its application. This defect is located in the color / varnish layer. It results in abnormal thickening in the final coat of paint or lacquer. It is the ripple of the surface in short wave. |
| Orange peel | Orange peel is an irregular formation on the surface, similar to the peel of an orange. It is due to the lack of stretching of the product during its application. This defect is located in the color / varnish layer. Results in abnormal thickening in the final coat of paint or lacquer It is the undulation of the surface in long wave. |
DOI and Orange Peel are physically similar surface effects but with different visual effects and are best seen at close range or long range.
Javier Echave
PHD, Chemical Engineer
Responsible for new R + d + i projects
SHARE: