Lighting Column Types
Obviously a great variety of lighting column designs exist from the functional to the more elaborate heritage or ornate columns. However, for conventional street lighting, the vast number of columns in the UK fall into one of the following main types.
a) Stepped Tubular Steel
Now the most frequently used column for conventional street lighting, consisting of a constant diameter column shaft with a larger diameter base compartment. The change in diameter is achieved by means of a short taper, frequently known as the shoulder. The angle of taper varies for different manufacturers and processes. the majority of columns have a single reduction although there are examples of tow or more.
b) Stepped Tubular Aluminium
Can be very similar to a) but aluminium extrusions can lead to greater variety including fluted shafts. The base compartment can also be formed by a casting which can be ornate and does not need to maintain a constant section.
c) Tapered Circular or Polygonal Steel
A constant taper circular section or a folded sheet polygonal section, which can be a regular or irregular polygon, generally with eight sides are quite common and can perform better in high wind exposure areas. A circular section with a constant diameter base compartment and a variable diameter shaft is also available.
d) Tapered Circular or Polygonal Aluminium
For aluminium the continuous tapered circular section is more common than a tapered polygonal section. Varying taper or multi stepped aluminium columns made from a single forming process also exist.
Concrete columns became very popular after the war and were in many forms with the flexibility of casting. Initially they were reinforced, but later generally tapered columns were prestressed with very ornate columns remaining as reinforced. In later years all concrete columns were spun to give a uniform dense outer surface. Standard production of concrete lighting columns stopped in the UK around 1998.
f) Cast Iron
Although more expensive than other materials the casting techniques allow greater freedom of design and permit very ornate columns for use in heritage areas and prestigious sites. Due to weight and casting costs they are generally only used for columns of limited height.
g) Composite or Polymer
As the name implies there have been a number of attempts to produce lighting columns of this range of materials, usually of a tapered circular section, but numbers remain small. They have potential for saving in maintenance and better performance under impact, but this has been offset by higher cost.
There are a few examples of solid or fabricated hollow wood columns, but the numbers are extremely small, although laminated wood columns have appeared recently. Columns that are merely clad in wood for appearance and not for structural strength are classified under the structural column type, usually tubular steel.
i) Passive Safety
The majority of columns are not designed to resist vehicle impact, but any column type can be tested under EN 12767 to determine the impact class of the design.
Clearly there will always be special designs in sympathy with a local landmark or design scheme but will generally be small in number for any one design.
k) Lowering Columns
There are many lowering columns on the market. These may be base or mid hinged with many of the preceding shaft types and materials.