Light Pollution

A work presented in the "II ENAST" and the "IV Brazilian Meeting on Astronomy Teaching"

(gif by Fabiola)

Fighting light pollution, an experiment in Nova Friburgo

José Carlos Diniz, Astrophotography Group from de RJ Planetarium, CARJ, REA, CANF.

Among all forms of pollution that harm our environment, the least known, but not the least pernicious is the light pollution. Its origin lies mainly on the excessive light emitted by badly designed luminous fonts that spread luminosity horizontally and upwards. These portion of luminosity does not contribute in any way to spread light into the evening darkness, because obviously, the only portion of light that is useful is the one directed downwards.

The main solution to the problem of light pollution lies in the effort to design light sources that would spread luminosity downwards from an imaginary horizontal plane, in such a way that the light bulb itself would remain invisible from the sides.

A really efficient light source should brighten the ground a little forward of half the distance between two light posts. In this manner, directing luminosity to where it is really necessary, less amount of light and electricity are required. Another additional advantage of such well-designed light sources is that human vision becomes less disturbed when there is no incidence of direct light over the eyes.

We need to end these old waste habits, and have no time to wait for any laws that would rule street illumination.

Considering the above stated, we decided to act in the small community of Muri, Nova Friburgo, where we have a small country house and a modest astronomical observatory.

We invited the workers from the local electricity concessionaire to look at the night sky, showed the effects of light pollution, and attracted their sympathy to the movement. The next step consisted in obtaining authorization from the local chief trustee to change some of the light sources. Once the authorization was given, we engaged in a field-work to document with photographs the different kind of sources and their pollution effects.

It became very clear that the angle of the sources where completely wrong, and the reflective and protection panels where too short, thus emitting light sideways. It would be necessary to recalculate the inclination angle of the sustentation arms and provide some additional lateral protection.

The astronomer Jorge Marcelino dos Santos Jr. (Planetário do Rio de Janeiro) helped us to recalculate the proper new arms angles and the lateral protection to achieve a good resulting illumination.

We started off by reinstalling the illumination in 10 lampposts. They had the proper angles of the sustaining arms adjusted, and an additional lateral protection was manually designed and installed. The effects on the resulting effects in illumination in the several stages where photographically documented. The results where better then expected, attracting the sympathy of the chiefe trustee and neighbors

This experiment will be expounded at the general meeting of inhabitants as an educational work and as a proposal to change all light sources.

At the area where these modifications where made one can see the sky clearly, the streets are better illuminated because of the optimization of the design of the sources and the lamp bulbs are not visible any more while driving through the street.

It is necessary to show people that the solution to this inconvenience does not mean a decrease in the global illumination, it is just avoiding to spread light to where it is not needed at all. In the present case the properly redirectin the light flux in fact increased the luminosity at the local area to the point that the original bulbs could now be changed to smaller ones, with the same resulting effect and some additional economy.

Trying to explain to a neighbor that he hasn't got the right to illuminate my house is not an easy task. Generally he will think that I want him to remain in darkness, but it was possible to show that is all a matter of wrong information, because when the results where seen the acceptance was general.

This is just an example of local action. I feel it is our obligation to fight all forms of pollution and waste in our environment.

This work is dedicated to Roberto Ferreira Silvestre for is fight against light pollution, an example to followed.

José Carlos Diniz