Traffic lights that can be easy on the eye during the day can be dazzling during the night.

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Saving energy by making use
of eyes' sensibility to contrast

By Professor Hugo D Godoy Azar*

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.

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.

The proposal
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.

Its application
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.

Environmental effect
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.

Final example
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?

*Thanks to:
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

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