BS 8408 : 2005 Selector Toolkit
The British Standard for Microprismatic Sheeting
Unique Approch
The new British Standard for Microprismatic Sheeting (BS 8408:2005) is groundbreaking in the sense that it is one of the first to be written from the perspective of the
driver, rather than how the products perform as they leave the factory. It’s vital that
road traffic signs are bright enough to ensure a significant proportion of drivers can
see and react safely to them. The standard describes this luminance requirement (sign
brightness) and rates how well a sign sheeting satisfies that need.
How much luminance a sign delivers to the driver will vary according to where the
sign is used and factors such as entrance angle, height, size and placement of the sign
relative to the road. The brightness of the surrounding environment will also have an
impact on how easily a driver perceives the sign.
The standard takes a unique approach in a number of ways:
Considers Vehicle Types
BS 8408 recognises that the truck driver’s need for sign brightness is the same as car
drivers. However, the standard provides separate ratings for sheeting performance for
truck and car drivers because virtually all retroreflective materials perform less well
for truck drivers because of their ‘disadvantaged’ position high above their headlights.
Considers Sign Types
Signs generally fall into two categories, those which are
mostly legend (directional) and those which are mostly
symbolic (regulatory and warning sign). Luminance
requirements for reading differ from those required for
recognising signs by their shape or symbols.
The Standard applies these different requirements by
creating two luminance ratings for each sheeting based
upon the type of sign it is used on.
3
BS 8408 : 2005 Selector Toolkit
Considers Sign Position
Along the road network signs are generally located in four positions: left verge, right
verge (or central reserve), overhead and low left. Car headlights deliver different
amounts of light to each of these sign positions. As a result a sheeting may satisfy a
drivers luminance requirement in one sign position but fail to deliver in another.
The standard calculates a position corrected luminance which is referred to as the
Performance Index.
Considers Night-time & Fluorescent Colours
In line with traditional standards BS 8408 establishes daytime colour requirements for
the sheeting but for the first time includes night-time colour requirements and colour
boxes for fluorescent sheetings.
Correct Specification
Specifiers can use the standard either to set a specified luminance performance
requirement for a sign or to determine from the sheeting manufacturers test results
whether it meets their requirements.
Taking all these factors into account, BS 8408 provides a way to rate how well a
microprismatic sheeting satisfies the needs of drivers for many frequently occurring
situations. Using this rating system, road authorities can specify microprismatic
sheeting with confidence.