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Signs of Many Colours

The Application of Colour in Variable

Message Signs

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Welcome from :

Mark Johnson Glynn Hutton

Technical Director Sales Manager

Signs of Many Colours

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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

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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.

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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.

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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.

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Signs of Many Colours

How can LEDs produce White Light?

Method 1

Use Red, Blue and Green LEDs

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Signs of Many Colours

How can LEDs produce White Light?

Method 2

Use a Blue LED coated with a Yellow Phosphor

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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.

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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.

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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.

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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)

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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.

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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.

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Signs of Many Colours

THANK YOU

Website : www.vmslimited.co.uk

Email: support@vmslimited.co.uk

Telephone: 0191 4237070

Time for Questions

http://www.vmslimited.co.uk/mailto:support@vmslimited.co.uk

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