Why Traffic Lights Use Red, Yellow, and Green Colors

Selecting and documenting traffic-signal indications

Colour is part of a defined display

Red, yellow or amber, and green are familiar traffic-signal colours, but a safe installation depends on more than the colour names. The indication may be circular or use a symbol, and its meaning depends on the applicable traffic rules and the way it is displayed. Signal sequence, flashing operation and arrow arrangements must follow the approved design.

A purchasing specification should show the required front view of every signal head. Mark the colour, symbol and position of each section. Identify whether the display uses separate optical units or a configuration with several indications in one unit. This gives the supplier a clearer reference than an informal description such as “three-colour traffic light”.

Check the complete optical configuration

Request the optical data and relevant test evidence for the selected signal module or head. Compare the proposed lens, colour and display arrangement with the project specification. Colour names alone do not establish a required optical performance, and a general claim about visibility through fog or rain should not replace the model-specific evidence.

Consider the whole installation, including the mounting position and the intended viewing area, through the responsible project designer. A change from a circular indication to an arrow or another symbol is a functional design choice, not simply a cosmetic change to an otherwise interchangeable product.

Keep replacement parts consistent

For replacement orders, identify the installed model, nominal size, supply and connector arrangement. Include photographs and the existing drawing where available. Confirm the exact colour and symbol for the replacement optical unit, and check whether associated drivers or other components must be matched.

Retain the approved configuration and drawing revision with the order. If the project uses a specific authority’s specification, send that requirement with the enquiry. GAOQIAO can then review the required signal arrangement and available product options against a concrete purchasing brief rather than an assumed universal sequence.