Doors, windows, conservatories and roof lanterns
Covering Guildford, Surrey, Hampshire and surrounding areas

Visual Quality of Double Glazing

Please read below for everything you need to know about visual quality of double glazing...

Double glazing provides a high standard of vision. The following is a guide to the quality that can be expected. Transparent glass used in the manufacture of insulating glass units is identical to that used traditionally for single glass and will, therefore, have a similar level of quality.

How to do a professional check

  • Stand in the room no less than 2 metres away from the panes and look directly through them. For toughened, laminated or coated glass, stand no less than 3 metres away. Do so in natural daylight, but not looking directly towards the sun and with no visible moisture on the surface of the glass. Where it is not possible to stand at the required distance, then stand as far away as you can from the panes.
  • Exclude from the check the 50mm wide band around the edge of the glass.

What to Expect

Flat transparent glass, including laminated or toughened (tempered) or coated glass is acceptable if the following are neither obtrusive nor bunched:

  • Bubbles or blisters
  • Hairlines or blobs
  • Fine scratches not more than 25mm long
  • Minute particles.

The obtrusiveness of blemishes is judged by looking through the glass, not at it, under natural light. It must be understood that the glass used in double glazing is not ground optically flat and so, as a consequence, blemishes are a possibility.

Special Glass

Toughened glass may show visual distortions which are accentuated by reflections in double glazing. Such surface colourations and patterns do not indicate a change in physical performance.

Laminated glass may have a few more blemishes due to it being made of several layers.

As a legal requirement, glass intended for use as a safety glass must display a permanent safety mark which is applied before installation, but which remains visible after installation. The mark must comply with the requirements of the British Standard BS 6206 “Specification for impact performance requirements for flat safety glass and safety plastics for use in buildings”, or its successor.

Low emissivity coating may produce transient visual effects. In oblique lighting the coating may look like a transparent film or produce a haze, ie., a cloudy look to the surface. When light coloured objects such as net curtains are placed close to the glazing they will look slightly darker.

Double Reflection

This occurs in certain light conditions. It is caused by multiple surface reflections in double glazing which may vary from pane to pane.

Brewster’s Fringes – The Rainbow Effect

Small transitory rainbow effects are sometimes produced by the glass deflecting light. Their appearance is due to high quality flat glass sheets being placed parallel to each other.

Patterned Glass

The above does not apply to patterned glass as its manufacturing process is different.

Call us on 01483 894489 … or email us on

Looking for double glazed windows, doors or conservatories in Guildford?

Experienced & Trustworthy

Family run and with over 28 years of experience, we promise a reliable and trustworthy service.

Our Safe Hands Guarantee

We’ll look after you from enquiry to installation and beyond with our aftercare and insurance backed guarantees.

Stress Free Installation

All our installers are Fensa approved and employed by us ensuring stress-free installation.

Vast Range of Products

We are independent so offer a large range of PVCu, aluminium or wooden, doors, windows, and conservatories.