What is a convex mirror?
Convex mirror definition: A convex mirror is a curved mirror wherein the mirror lense is curved outwards, the centre of the mirror bulges toward the viewer. A convex mirror may also be simply called a curved mirror, a fisheye mirror or a diverging mirror. The outward bulge or curve of the mirror expands the visible field presented in the mirror reflection. This makes convex mirrors highly suitable for security and safety applications where they are used to expand and improve visibility.
This type of mirror will reflect a wider field of view than a standard flat mirror and the more pronounced the dome, the wider the reflected field of view will be. While you can therefore use a convex mirror to provide a wider angle of view, the curvature of the mirror itself, means that there will be some distortion of the reflected image.
If you have ever visited a crazy hall of mirrors at a funfair, you will have seen curved mirrors which have been taken to the extreme for maximum distortion, with the outward curved convex mirrors reflecting an extremely fat body, while the inward curved concave mirrors reflecting you with an ultra skinny figure!
What types of convex mirror are available?
Convex mirrors are used in a wide range of safety and security applications along with search and inspection.
Their versatility means that convex mirrors are available in a range of materials and sizes and with a variety of coloured frames to choose from (to meet industry standards for certain types of application or simply to help the mirrors blend into the surrounding environment).
External grade mirrors are manufactured from materials which will withstand weathering (there are even frost free and anti condensation models available) and typically, they come with more robust fixings and brackets than are used with interior mirrors which don`t have to withstand possible movement or realignment caused by strong winds.
Where can I use a convex mirror?
As long as your mirror is not positioned in such a way as to invade the privacy of others, convex mirrors are useful for a wide range of applications including; traffic related applications, as a parking aid, for school safety and retail security use and of course for use as search and inspection mirrors.
Traffic related applications include mirrors positioned to eliminate blind spots for drivers exiting from a home driveway, commercial site exit or at a tricky "T" junction where two or more roads meet, often such mirrors will have a distinctive coloured frame to draw the attention of drivers to their presence as a helpful aid. They are also ideal for use as a driver aid where a driver has to park in or negotiate tricky or tight spaces.
Industrial uses include; use in and around warehouses, enabling fork lift truck drivers to see around corners to help avoid collisions with other trucks or pedestrians, as a safety aid in and around vehicle compounds, delivery and dispatch areas, etc and of course at site entrances and exits.
In shops and retail environments, convex mirrors offer a practical, low cost alternative or addition to CCTV monitoring systems. Traditional style round or rectangular mirrors can be fixed to walls or convenient poles or roof support columns, while ceiling dome mirrors provide a simple method of monitoring shopping aisles which would be concealed from direct line of site at ground level.
The convex shape also makes this type of mirror ideal for use as a search or inspection mirror as the convex surface maximises the area reflected.
What materials are convex mirrors made of?
Convex mirrors are available in a range of materials - here is a quick guide to the materials typically used to manufacture the reflective mirror lens;
Glass is an old favourite as it typically reflects a crisp, clear image. On the downside however, glass is relatively fragile and is heavy when compared with plastic type material alternatives such as acrylic or polycarbonate.
The risk of breakage on impact, also makes glass a less than ideal choice where there is a risk of vandalism, or where the mirror is installed in a public place where there would be a risk of injury to customers, staff, or visitors etc. from glass shards in the event of a breakage.
Acrylic is a generic term used to describe the material used to manufacture many plastic type budget mirrors because it is relatively cheap.
On the plus side, it is a lightweight material that when well manufactured can produce a reflection equal to that achieved with a glass mirror.
On the downside acrylic will shatter on impact which could result in sending sharp shards flying which could cause injury. For that reason, use of acrylic mirrors is not recommended for use in public areas. There are however various grades of mirror sold under the acrylic description, some of which are safer than others as while they will still break on impact, are less prone to fragmentation. Plastic is a softer material than glass and is therefore more easily scratched, which means that it should be cleaned with care (typically simply washed down with clean water and a soft cloth)
Polycarbonate is again typically used as a generic term to describe an alternative type of plastic mirror material such as polycarbonate, polymir, etc.
Polycarbonate mirrors differ from acrylic mirrors in as much as they are virtually unbreakable (approx 200 times as strong as glass) and will withstand even heavy impacts making them ideal for use as traffic mirrors or use in harsh environments, etc.
Unfortunately the manufacture of a high quality semi rigid polycarbonate mirror is a more costly process than that of an acrylic mirror, which is why the selling price has to be higher.
There are however some budget mirrors (typically some cheaper type driveway mirrors, etc) which feature a thin and flexible polycarbonate mirror lens. Whilst these units will withstand the impact of a flying stone thrown up by a passing vehicle for instance, the flexible lens may lead to some minor distortion of the reflected image. This is unlikely to be a problem with a mirror used to increase visibility at a blind spot such as a home driveway exit onto a busy road, but may make such a mirror unsuitable for a more demanding application.
Polycarbonate is a plastic type material which is softer than glass and therefore more easily scratched. Some polycarbonate convex mirrors are available with a special scratch resistant surface which is a help, but like all plastic mirrors, cleaning should be undertaken with care (typically simply washed down with clean water and a soft cloth).
Stainless steel is also used to manufacture mirrors. This is a robust but expensive material and involves an expensive manufacturing process including a finishing process to produce a highly polished reflective surface, which is why stainless steel mirrors cost much more than glass or plastic alternatives.
Such mirrors are often used in vulnerable areas where there is a high risk of vandalism, however being metal, any impact is likely to result in a permanent dent in the mirror surface which would be costly to repair and the surface may require specialist re-polishing from time to time.
What shapes and sizes of convex mirrors are available?
Convex mirrors are available in a range of shapes and sizes making them suitable for a wide range of applications. Popular mirror shapes include round, rectangular and hemisphere and part hemisphere formats.
Sizes are normally expressed as metric measurements (i.e. centimetres or millimetres) although mirrors imported from or destined for the USA will normally be measured in inches. Whatever the unit of measurement used, it will normally represent the size of the mirror lens itself, so the overall size inclusive of the mirror frame will be larger.
Round mirrors are measured across the diameter, with popular sizes ranging from 450,600,800 and 1,000mm.