What Is Reflex Glass?

Reflex glass, often found in level gauges, uses a prismatic structure to clearly indicate liquid levels in tanks. Its design reflects light differently when in contact with liquids versus gases, providing a high-contrast, easy-to-read visual cue. Intrigued by how this simple yet ingenious technology safeguards industrial processes? Discover the mechanics behind reflex glass and its critical role in monitoring systems.
Andrew Kirmayer
Andrew Kirmayer

Reflex glass generally reflects light that comes in from the outside. It often has grooves shaped at 45° angles, enabling a light wave to pass into a liquid or gas chamber where its speed changes, resulting in a shift in direction. The phenomenon of refraction is usually the principle behind using this glass, and the property in a material that changes light direction and speed is called the refractive index. Grooves in reflex glass can have reflecting prisms etched in, which can break the light wave up into its parts. Often used in scientific instruments, reflex gauge glass helps to determine the liquid or gas content in a sample based on the reflection and refraction of light that passes through.

If there is gas in a gauge, for example, the area will be bright since the light usually passes through at a 45° angle. Typically no refraction takes place, which can cause the light to turn at a right angle and appear as a silver color. When liquid is in a chamber, the light will continue to pass into the sample and be refracted. The walls in this kind of gauge usually do not reflect light, which is often absorbed by the liquid. A dark coloration usually appears inside when someone looks through the glass into a liquid sample, even if the fluid is colorless.


Gauges with reflex glass are often used in laboratories because of their low cost to purchase and operate. Scientists and researchers can also benefit from the convenience of reading them over other types of instruments. The devices, however, cannot show a separation between different liquids or the actual color of the fluid. They are generally not suitable for use with corrosive fluids or high pressure steam or water.

Such instruments can be designed as glass tube indicators, level gauges that are welded to a container, bull’s-eye process gauges, or magnetic level indicators. Other reflex glass products are used for gauges on water boilers. Glass on waterproof Liquid Crystal Display (LCD) televisions and ultraviolet light reflecting components on printers often have reflex properties as well.

Aside from a grooved structure, reflex glass can be smooth and elongated or circular in shape. Sometimes, the properties of this type of glass can inhibit an application. Products with anti-reflex properties, which can transmit light even more effectively, have been made as a result. Solar glass is an example because a maximum level of light is typically required to generate electricity.

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