Document Ref : PRES000019 Rev A Signs of Many Colours The Application of Colour in Variable Message Signs
Document Ref : PRES000019 Rev A
Signs of Many Colours
The Application of Colour in Variable
Message Signs
Document Ref : PRES000019 Rev A
Welcome from :
Mark Johnson Glynn Hutton
Technical Director Sales Manager
Signs of Many Colours
Document Ref : PRES000019 Rev A
Introduction
LED displays are now available with a wide range of different colour
options. This purpose of this presentation is to:
•Give some general background information on Colour theory
•Describe how LED’s produce different Colours
•How do we define Colour
•Describe the requirements of Colour in Road Side Displays
•Describe the alternative approaches to multi-colour signs
Signs of Many Colours
Document Ref : PRES000019 Rev A
Signs of Many Colours
What is colour?
Our eyes are sensitive to
electromagnetic radiation
which has wavelengths in the
range of about 380nm to
740nm.
About 44% of the energy
radiated by the Sun is in this
range of visible light.
Document Ref : PRES000019 Rev A
Signs of Many Colours
How do we see colour?
Our eye have two types of light sensitive receptors, cone and rods.
The rods are primarily used for low light conditions and give very
sensitive black and white vision.
Cones are sensitive to specific wavelengths of light and are grouped
in 3 ranges, Low frequency light (Red), Medium (Green), High (Blue).
Our brain combines all this information to allow us to see colour.
People with Colour blindness or Colour Vision Deficiency either have one or more sets of cones
missing or more commonly one of the sets of cones is shifted which reduces the ability to
differentiate between colours.
The most common form of colour blindness present in 6% of men causes the green cones colour
response to be shifted towards red. This results in a reduced sensitivity to the green area of the
spectrum.
Document Ref : PRES000019 Rev A
Signs of Many Colours
How do LEDs produce Coloured Light?
An LED is just a diode which happens to produce
light.
A diode works by putting together two different
materials which allow electrons to pass easily
in one direction but not the other. This process
causes the electron to change its energy level.
When the electron moves to a lower energy level
some energy is released.
In LEDs this release of
energy is in the form
of light.
LEDs use different
materials to produce
different wavelengths
of light.
Document Ref : PRES000019 Rev A
Signs of Many Colours
How can LEDs produce White Light?
Method 1
Use Red, Blue and Green LEDs
Document Ref : PRES000019 Rev A
Signs of Many Colours
How can LEDs produce White Light?
Method 2
Use a Blue LED coated with a Yellow Phosphor
Document Ref : PRES000019 Rev A
Signs of Many Colours
CIE 1931 Colour Chart
Almost all light sources emit a range
of frequencies of light.
Even LEDs which are thought of as
mono-chromatic emitters actually
emit a band of frequencies.
Therefore we do not define colour
simply as a single frequency but as a
X,Y coordinate on a colour chart.
Document Ref : PRES000019 Rev A
Signs of Many Colours
CIE 1931 Colour Chart
The colour standards for road
signals are defined as areas on
this colour chart. (As defined in EN12966)
The colours have been selected
to give the best possible colour
separation and allow as far as
possible for drivers with impaired
colour vision.
For example traffic signal Green
is not a pure green but a bluish
Green.
Document Ref : PRES000019 Rev A
Signs of Many Colours
CIE 1931 Colour Chart
The colour standards for road
signals are defined as areas on
this colour chart. (As defined in EN12966)
The colours have been selected
to give the best possible colour
separation and allow as far as
possible for drivers with impaired
colour vision.
For example traffic signal Green
is not a pure green but a bluish
Green.
Document Ref : PRES000019 Rev A
Signs of Many Colours
So what is colour temperature?
Colour temperature is used to define the ‘warmth’ or
‘coolness’ of different light sources. It is measured in
Degrees Kelvin (K).
Colour temperatures above 5000K are called Cool Colours
(blueish white).
Colour temperatures below 3000K are called Warm
Colours (yellowish to redish white)
Document Ref : PRES000019 Rev A
Signs of Many Colours
Why is colour so important for Variable Message Signs?
Road signs give information and instructions to
drivers.
The colour definitions are the same as those used
in other road lighting applications, Traffic signals,
External Vehicle Lights.
We use colour in VMS to allow a wider range of
messages and aspects to be displayed.
Document Ref : PRES000019 Rev A
Signs of Many Colours
RGB or 5 Colour?
For TV’s, PC Monitors, Video Walls, RGB is by far the most common way of
producing a large range of colour. This would seem to be the obvious choice for
multi-colour VMS?
However an RGB LED display cannot
produce all the 5 colours defined for VMS.
It also relies on mixing LED colours,
which requires very fine luminance
control and can drift over time.
Document Ref : PRES000019 Rev A
Signs of Many Colours
THANK YOU
Website : www.vmslimited.co.uk
Email: [email protected]
Telephone: 0191 4237070
Time for Questions
http://www.vmslimited.co.uk/mailto:[email protected]
Document Ref : PRES000019 Rev A