Über Notlicht | 20. March 2017

Why are escape signs green?

Everybody knows them, the green signs with arrow, which help us to leave a room, a building section or a building safely in case of danger. Those escape sign luminaires with green-white luminaires are an essential part of safety lighting. But why are they green?

There are guidelines for the appearance of escape signs, so that they can be recognized as such already at first glance. Those guidelines are regulated by various standards and regulations.

Since 2013 the general appearance of escape signs according to the international standard ISO 7010 is mandatory.   This is intended to ensure that a uniform marking leads to less problems of understanding. This means that no text is used, as this could lead to misunderstandings among foreign-language people. The forms and colours are based on ISO 3864.

But why green?

To answer this question, we have to take a closer look at medicine.

The retina in the human eye consists of several cell layers, the rearmost layer (consisting of rods and cones) is responsible for converting the incident light in signals.  The rods are „colour-blind“ and can only process light intensities. The cones allow colour vision and light-dark perception.

Since the rods react particularly strongly to blue-green light (with a wavelength of about 500nm), the sensitivity of the human retina shifts in this direction during darkness. Pictures are perceived differently during the day than in the dark. In sunlight, for example a red appears more vivid and brighter, while at night the green and blue tones are perceived as brighter.

Since escape signs should be bright and clearly visible in periods of limited visibility, such as darkness (power failure) or smoke development, they are kept in green.

A pictogram (symbol) in white, which explains the respective information of the sign to the viewer, is depicted on an escape sign. The images are reduced to the essential and kept gender- and culture neutral, which ensures the international understanding of the signs. All symbols are white (RAL 9003 signal white) on a green (RAL 1632 signal green) background according to DIN 5381.

However railway, tram and subway tunnels are exceptions. Emergency exits are marked with blue signs to ensure, that they aren’t confused with the green railway signals.

If you see red signs, then these are prohibition or fire protection signs, yellow means warning and mandatory-signs are kept in blue.

On customer request we produce almost an unlimited range of special pictograms. Just send us your request and let us know what you want.

But why green?