Measuring Gloss with the PosiTector GLS Gloss Meter

Referenced products:

Consumers love gloss—this can be seen in almost every industry from automotive, to electronics, to baby toys. No matter the industry, gloss tends to be associated with luxury and wealth. Studies suggest that humans’ innate love for glossiness could be based on the biological need for water: the glossier an object, the more likely to ‘quench thirst’.

From an industry standpoint, gloss can have a very specific purpose. By definition, gloss is an optical property that indicates how well a surface reflects light in a specular (mirror-like) direction—or, how lustrous or shiny an object appears. While many industries prefer a glossier finish, some require a more matte finish.

Why Measure Gloss?

Measuring gloss while a product is being manufactured can improve the production process by identifying process issues, maximizing consistency, reducing waste, and improving overall quality. Surface texture, coating properties, and paint application can all have an effect on a coating’s appearance. While it’s easy for the human eye to detect large differences in gloss, like comparing a matte finish on a military asset to a glossy red sports car, smaller differences in gloss can be harder to see—but can still have a big impact on process control.

Image depicting an object with a matte finish next to one with a glossy finish

What is Reflectance?

When light hits a surface, some of it is absorbed, and some is reflected. The reflected light is responsible for how the object is perceived. The nature of the reflection is generally related to the surface finish of the object. On a smooth, polished surface like a mirror, light is reflected opposite to the angle at which it arrives; this is referred to as ‘specular’ reflection. On a rough surface, light is reflected at all angles and a relatively small amount of light reflects at the specular angle.

Illustration depicts how light specularly reflects off of smooth surfaces vs a diffuse reflection on rough surfaces

What is Percent (%) Reflectance?

Reflectance is a measurement of the amount of light detected versus the amount of light sent and is expressed as a percentage. Gloss meters such as the PosiTector GLS can display in both GU and percent reflectance directly on the gage.

What is Gloss Value? What are Gloss Units?

Per ISO 2813, Gloss Value is a ratio of the reflectance of the test specimen to the reflectance of a standard polished black glass surface “with a refractive index of 1,567 at a wavelength of 587.6 nm in the specular direction”, multiplied by 100. It is expressed in terms of Gloss Units.

What is Haze Index?

Haze is the appearance of a “milky” halo or bloom perceived in reflective surfaces caused by microscopic imperfections in the surface’s texture. Haze Index is calculated and is defined by ASTM D4039 as the difference between gloss values measured at 60° and 20°. The PosiTector GLS 20/60 and 20/60/85 are capable of calculating haze when selected within the Setup menu.

How is Gloss Measured?

Digital gloss meters like the DeFelsko PosiTector GLS Gloss Meter measure the surface using a calibrated light source and light sensor at opposite, specular angles to each other. Reflectance is determined by comparing the amount of light energy emitted by the source with the amount of energy received by the sensor. Gloss is then automatically calculated using a look-up table.

The PosiTector GLS Gloss Meter includes a reference standard built into the base of the unit. When turning the unit on or when selected from the menu, the instrument automatically calibrates itself using the known Gloss Unit values of the standard.

Choosing the Best Angle for Gloss Measurement

On most surfaces, as the viewing angle increases, the reflectance and Gloss Value also increase. This is often apparent to the naked eye: for example, on the case below there is little apparent reflectance when viewed from above, but when that same case is viewed from a wider angle (nearer to the surface), visible reflectance can be seen. This phenomenon can be used to provide greater measurement resolution on high-gloss and matte finishes.

Image depicts how reflections on matte surfaces are more apparent when viewed at a shallow angle

To determine the correct gloss measurement angle, gloss is first measured at a 60° angle:

  • If the result is between 10–70 GU, the object in question is considered semi-gloss and the 60° measurement angle is appropriate.
  • If the result is greater than 70 GU, the surface is considered high gloss and should be measured with the 20° angle.
  • If the result is less than 10 GU, the surface is considered matte and should be measured with the 85° angle.
Chart depicts when to switch measurement angles with the PosiTector GLS based on reading from the 60° angle.

How to take Gloss Readings with the PosiTector GLS Gloss Meter

The PosiTector GLS Gloss Meter is available in three models:

  • PosiTector GLS 60° for measuring most gloss applications and is the preferred angle for semi-gloss
  • PosiTector GLS 20°/60° for measuring high-gloss to semi-gloss and calculating Haze Index
  • PosiTector GLS 20°/60°/85° for measuring high-, semi-, and matte gloss levels and also calculating Haze
Chart depicts the differences between PosiTector GLS probes models

Taking gloss measurements with the PosiTector GLS Gloss Meter is fast and easy:

1. It is critical that the calibration tile stays clean to verify the accuracy of the meter. Periodically, or when dirt or debris is visible, the gloss standard should be cleaned using the included cleaning wipes. Once the self-check is successful, the PosiTector GLS is ready to measure.
Image demonstrates how to clean the PosiTector GLS calibration tile
2. Before powering the gage on, ensure that the protective base plate is securely on the probe. When powered on and with Power-On Cal enabled, the probe will automatically perform a self-check and calibration using the calibration standard incorporated into the protective base plate; traceable certificates of calibration are included for both the probe and the gloss standard.
3. Remove the protective base plate from the probe and place the probe on a firm, flat surface. Simply press the button to take a reading; the gage will beep twice and a measurement will be displayed.
Image shows the PosiTector GLS taking a gloss measurement on a red painted test specimen

Features of the PosiTector GLS Gloss Meter

The PosiTector GLS boasts multiple measurement modes and helpful features that make it suitable for nearly any application:

  • HiLo mode: for quick inspection or pass/fail checks
  • Differential Mode: automatically calculates the difference between current reading and stored reference value*
  • Normal Scan Mode: measure and save up to 120 readings per minute*
  • Statistics Scan Mode: continuously measures and displays real-time statistics, saving each scan into memory*
  • Alternate Calibration Standards: store multiple calibration standards (tiles) for quick calibration adjustment

*Available on PosiTector GLS Advanced models only

Since it is part of the PosiTector platform, the PosiTector GLS is compatible with any PosiTector probe; quickly converting from a gloss meter to a coating thickness gage, surface profile gage, environmental meter, and more. It also has the added benefit of a large 2.8” impact resistant color touchscreen, and an easy-to-use menu. Advanced gage bodies can connect to personal smart devices or laptops via WiFi or Bluetooth.

Manage Gloss Measurement Data with PosiSoft Software

When gloss inspection is complete, download the readings using the built-in USB port, or via WiFi if using an Advanced gage body. When connected, download, view, and print stored readings in professional PDF reports quickly and easily with PosiSoft Desktop software. Fully customized reports can be created to match existing paper forms or layouts.

PosiSoft Desktop screen capture with PosiTector GLS measurement data


While gloss measurement is often done for aesthetic reasons, measuring gloss can have a big impact on process and quality control. The PosiTector GLS Gloss Meter comes fully featured to handle many gloss measurement applications. Watch the video below or view the product page for more information.

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