Outdoor Area lighting is considered to be one of the major contributors to sky glow. Cut-off optical systems are helping to address the problem, but this is not the only alternative. Lamp dimming should also be considered as a means towards reducing nighttime brightness and achieving dark skies. Dimming does not change the distribution of the illumination. It just reduces it in the same proportions. Dimming also dramatically reduces the upward reflected light from the roadway, as this is another major cause of sky glow.

Outdoor Area lighting is designed to IESNA recommended levels that meet the requirements of maximum vehicle and pedestrian activity. Traffic activity varies from maximums at peak morning and afternoon “rush hours” to little if any activity during the late evening and early morning hours. Traffic is significantly lighter between 11:00 pm and 6:00 am.

Until now, lighting systems lacked the flexibility to accommodate these various levels of activity. They were usually designed to the High level. This means that we can dim the lighting by 50% if the traffic activity diminishes accordingly. In most cases we can significantly reduce nighttime lighting levels and sky glow and still remain well within IESNA recommended levels.

There are significant advantages to dimming outdoor area lighting with a 50% reduction in sky glow, offending glare, and light trespass and a 40% saving in the energy consumed by lighting during the nighttime period. The related cost savings for the power and its delivery are significant.

Fossil fuels are used to produce a good portion of the electrical power. We can reduce CO2 emissions by up to 40% by incorporating dimming into our roadway lighting systems. Lower emissions produce an atmosphere that is cleaner and cleaner air results in a clearer nighttime sky.

There are a number of outdoor area lighting dimming control systems presently available on the market. There are multi-stage dimming systems, controls that can monitor power usage by fixture, systems that can provide a constant light level as the lamps age and simple ‘high-low’, time activated controls. Some designs are connected to a central station, some use GPS technology and some act independently on their own. There are now control systems for every requirement and budget. The choice in the degree of complexity is yours. Dimming controls should be robust and reliable because they are mounted at the top of a 30’ or 40’ pole, and they should last as long as the lighting system, usually up to 20 years. The control should also fail to the ‘High’ original design setting in the interest of safety.

Some provincial governments and utilities are beginning to provide financial incentives toward lighting controls. This will help to reduce the payback period. When weighing the investment in dimming systems we must avoid comparing them to the original cost of the luminaire. We must look at the power cost saving and the ongoing benefit that the dimming control is providing to the environment, to our health and to the night sky.

Dimming is one of the most effective tools toward reducing sky glow. The use of roadway lighting dimming controls is making a quantum leap towards claiming back our night sky.

Michael Barry
President
MJB Technologies