Anti-reflective glass is a glass coated with a special process, which has a particularly low light reflection of 1% compared to 8% commercially available glass. It offers maximum transparency, is almost invisible and is particularly suitable for night use, as there are no disruptive reflective effects from lighting.
How do reflections arise on anti-reflective glass panes?
Reflections occur when light hits the interfaces of media of different optical densities. Air has a refractive index of 1, while float glass has a value of 1.52. This then leads to the well-known reflections of a window glass, which reflects approx. 8% of the incident light.
This reflection behavior can be specifically influenced by a suitable selection of layers with different refractive indices. The reflection can be reduced to approx. 1% with just 3 layers. Anti-reflective glass is available in almost every common type of glass. These include float glass, white glass, laminated safety glass, toughened safety glass and also insulating glass.
How these glass produced
While in the past glass was often anti-reflective by means of a fine etching (silk matting) on the surface, a special optical interference coating is used today, which makes the glass as good as invisible. To do this, a film of liquid, the so-called “sol”, is first applied to the glass. Thanks to the humidity in the air, the sol turns into gel, which is then firmly bonded to the glass using a chemical-technical process – a so-called “pyrolytic fixation”.
The pyrolytic process comprises two steps: First, the liquid film (“sol”) made of high molecular weight, organometallic substances is applied to the unheated glass surface. The coating process takes place under clean room conditions. Several Titanium dioxide and Silicon dioxide layers are applied. This is usually done over an immersion bath or by rolling up or spraying on the sol layer.
The use of different metal oxides creates a combination of high and low refractive index layers. These interference layer systems consist of a number of thin layers with different optical properties and thicknesses.
By absorbing atmospheric moisture, the coating is transformed into a gel film. This is followed by pyrolytic fixation, in which the coating is burned onto the glass surface as a solid layer.
