Traffic lights that can be easy on the eye during the day can be dazzling during the night.
About us | Quiénes somos
How good is your Mayor?
Urban energy saving (USA)
Urban ecological footprint
Cities' green policies
US cities to go green
Cities and biodiversity
Mexico City garbage disposal
Saving energy by using contrast
Great Lakes initiative
Issues facing megacities
Dubai & Shanghai development
Pros and cons of biofuels
Smart growth in US cities
Greenest US cities
US mayors agree on Kyoto
Most polluted US cities
City Mayors reports news from towns and cities around the world. Worldwide | Elections | North America | Latin America | Europe | Asia | Africa |
Mayors from The Americas, Europe. Asia, Australia and Africa are competing for the annual World Mayor Award. More
City Mayors ranks the world’s largest as well as richest cities and urban areas. It also ranks the cities in individual countries, and provides a list of the capital cities of some 200 sovereign countries. More
City Mayors reports political events, analyses the issues and depicts the main players. More
City Mayors describes and explains the structures and workings of local government in Europe, The Americas, Asia, Australia and Africa. More
City Mayors profiles city leaders from around the world and questions them about their achievements, policies and aims. More
City Mayors deals with economic and investment issues affecting towns and cities. More
City Mayors reports on how business developments impact on cities and examines cooperation between cities and the private sector. More
City Mayors describes and explains financial issues affecting local government. More
City Mayors lists and features urban events, conferences and conventions aimed at urban decision makers and those with an interst in cities worldwide. More
City Mayors reports urban environmental developments and examines the challenges faced by cities worldwide. More
City Mayors reports on and discusses urban development issues in developed and developing countries. More
City Mayors reports on developments in urban society and behaviour and reviews relevant research. More
City Mayors deals with urban transport issues in developed and developing countries and features the world’s greatest metro systems. More
City Mayors examines education issues and policies affecting children and adults in urban areas. More
City Mayors investigates health issues affecting urban areas with an emphasis on health in cities in developing countries. More
City Mayors examines the importance of urban tourism to city economies. More
City Mayors examines the contributions history and culture make to urban society and environment. More
City Mayors describes the history, architecture and politics of the greatest city halls in the world. More
City Mayors invites readers to write short stories about people in cities around the world. More
City Mayors questions those who govern the world’s cities and talks to men and women who contribute to urban society and environment. More
City Mayors profiles national and international organisations representing cities as well as those dealing with urban issues. More
City Mayors reports on major national and international sporting events and their impact on cities. More
City Mayors lists cities and city organisations, profiles individual mayors and provides information on hundreds of urban events. More
Saving energy by making use
5 November 2008: We are consuming, and wasting, vast amounts of energy. This must be changed. My idea involves changing a 60-year-old concept in the way that traffic lights work all over the world and how they waste money and energy. What follows is a summary of the work undertaken in mechanics and electricity, which won approbation at the Polytechnic University of Catalonia.
of eyes' sensibility to contrast
By Professor Hugo D Godoy Azar*
Debate this article
For thousands of years mankind has used light (fire) to illuminate objects in the absence of natural light, shaping the idea that light is to be used to illuminate things and the more intense the light, the better things are seen.
It is barely a century since we invented the means of using artificial light, varying its intensity, frequency, and colour. These new possibilities have allowed us to use it for other functions such as signalling, warning, or organising - that is, we no longer employ lights merely to see things. The lights themselves are to be seen, and not only at night or in dark places but in daylight as well. They no longer serve simply as vehicles of illumination.
The idea that will now be explained arises from observations of the function of lights to control traffic flow - traffic lights, illuminated signs, and so on, the purpose of which is not to illuminate as such, but rather to be seen as lights of warning, instruction or information that function day and night.
Summary of the idea
The human eye contracts or dilates the pupil in response to the quantity of light received. The greater the light the more it contracts, and conversely dilates with decreasing light, such as at night. Therefore we possess the capacity to increase or diminish our ability to perceive light. Our ability to perceive light is not constant. It is better at night.
Two interesting topics to be considered are the effects of ‘dazzle’ and ‘invisibility’, or scientifically speaking, ‘high contrast’ and ‘low contrast’. For example, at night we are dazzled by a car’s headlights (high contrast) while during the day the stars become invisible (low contrast).
The notion of ‘sensibility to contrast’ represents the ability of the visual organs to distinguish between object and background. And we are simply not making the most of that innate ability. At night the background is dark and the contrast high, so it is easier to see lights such as the stars.
Our central thesis is that if we could make full use of this, we would achieve enormous improvements in electricity savings and efficiency as well as in road safety. We submit that traffic lights should operate at different intensities. They should be higher by day so that they can be more readily seen. This is where the contrast is minor because the environmental light is high. At night there should be weaker intensities, taking advantage of low environmental light and high contrast. Such a correction at night would save much money and energy and also avoid the hazards of ‘dazzle’.
Though it is not the specific aim of this proposal, it should be mentioned that as a result of their very high intensity at night, some lights especially, the new LED semaphores, could ‘dazzle’ visibility and affect road safety.
Based upon the original concept outlined below, we propose a change that goes against the grain of 60 years experience of doing things in a particular way. We consider it to be a necessary change in order to save energy and money and to stop wasting it.
If a specific 150 watts light source can be seen well in daylight, this same light can be seen just as well at night with 20 watts intensity. By using only the energy required for the light to be seen, we can make much more efficient use of resources.
The combination of electrical intensity controls and light sensors is an easy task and does not require developing new technology. The sensor could be regulated so that the intensity of the environmental light, day or night, gives a signal to the regulator to increase or diminish the quantity of light. It could be applied to all existing lights, including modern LED, without the necessity of replacing them. Moreover, this idea could be extended to all lights, not just traffic lights.
Traffic lights work 24 hours a day 365 days a year!
In Spain there are approximately 300,000 of them using 1,200 kilowatt-hours each per year. Considering the number of hours of nights, dusks, dawns, cloudy days, we could consider a saving of 50 per cent of that energy, depending on the particular country.
Limitations do not allow us to formally prove and certify those assertions. But regardless of the accuracy of these calculations I believe that it is evident that the amount of energy we could save would be more than substantial.
Investment and amortisation
Based upon the previous two points, we can see that the cost of the small investment required to modify them would soon be amortised.
I invite you to try an exercise of observation that clearly illustrates our idea:
At night, proceed to a wide straight avenue, if possible 500-metres long, with traffic lights working at the end. You will see that despite the distance, you will be able to see clearly the lamps of the traffic lights, which have a minimum of between 75 and 150 watts. Wait until a car arrives and stops at the lights. You will be able to see clearly its rear lights of 5 watts! Intriguing, isn’t it?
City Mayors, for the opportunity of spreading this idea.
And to all readers, for reaching this point.
Dedicated to my parents Abel and Elvira
Prof. Hugo D. Godoy Azar
Comment & Debate
City Mayors is inviting its readers to engage in a debate on the issues raised in the article on this page. Please post your comments below. Your comments should deal with the topics of this article and must be legal and ethical. You may also reply to and/or challenge comments of other readers. While we endeavour to publish all relevant comments, we reserve the right to edit them and to reject unsuitable contributions.
Please add your comment
The best Mayors for Stronger | Fairer | Greener cities. Elect your candidate for the 20/21 World Mayor Prize and Honours. The Prize has been awarded since 2004.