Twilight Switch: Working Principle, Applications, Advantages

How many times have you admired the reflection of the dawn and the clarity of its light? How many times have we stopped, mesmerized, to look at the wonderful colors and the beauty of a sunset or to wonder about its magic? These are amongst the most fascinating phenomena that nature can offer, they bring out our more romantic and less emotional side.

As technicians, moreover, we are inclined to find a more scientific definition for twilight, due to professional training and necessity. Finding an exhaustive definition is, however, not banal in the least. The problem dates back more than two thousand years ago. On the one hand, the necessity to find a definition for natural phenomena and the need for societies to use daylight hours on the other have driven scholars, down through the centuries, to define and capture twilight. The ancient Romans called it “crepem” or “nearly dark”. The ancient Greeks called it “amphiluce” or “doubtful light”.

Even today, not so differently from two thousand years ago, it is evident that there is a lack of a universal definition upon consultation with the scientific community. “A sunset is an intellectual phenomenon”, according to Franceso Pessoa. Twilight, is in fact, complex and difficult to define since it is influenced by multiple factors, such as latitude, season, month, weather conditions, transparency of the atmosphere, and declination of the sun. On a scientific level, there are three distinct definitions of twilight, which are astronomic, civil and nautical. It is ascertained on the basis of the inclination/depression of the sun in relation to the horizon, keeping in mind the degree of visibility of objects and stars. The civil twilight, particularly, is defined by the time interval in which the sun shows depression of between 0° and 6°. In reality, when the height of the sun is equal to -6° street lighting is turned on.

The exact definition of twilight in relation to time, is today indispensable, even from an energy-saving point of view. In fact, it is even more important to adopt technologies that allow for reductions in consumption and pollutant emissions ensuring contained costs at the same time.

From this point of view, the crucial question is whether a device exists which can program the turning on/off of street lighting or lighting in shop windows based on the quantities of available sunlight without having to monitor or perform any actions on a daily basis.

Is it possible, rather, to have an effective assessment mechanism, which regulates, independently from location, season and weather conditions, the operation of a lighting system?

Yes, it is…

What is a Twilight Switch?

The twilight switch is a control device used to switch lighting circuits remotely according to the scheduled level of the ambient light detected by a special sensor. The switch-on and off threshold can be adjusted by the user. It is suitable for use in places such as shop windows, street lighting, car parks, animal breeding facilities, highways, secondary roads and telecom stations where automatic control of lighting is required.

Using a twilight switch can prevent the unnecessary use of lighting circuits where sufficient daylight increases. As it allows for to reduce of energy consumption, it can be used in external places like gardens, parks, parking lots, entrances, courtyards, etc.

How Does a Twilight Switch Work?

The twilight switch allows to switch ON and switch OFF lighting devices according to a scheduled level of the ambient light. It is used in combination with an external sensor to detect if the ambient light is higher or lower than the set level.

When the external light falls below a certain level (e.g. during the evening when the shop is closed), the device switches on the lights. When the external light returns to above the threshold value, the twilight switch relay returns to the open position.

The circuit of a twilight switch requires other components such as control relays and power contactors when you want to control a higher electrical power (lamps, electrical appliances, etc.).

The twilight switch is suitable for use in places such as shop windows, street lighting, car parks, animal breeding facilities, highways, secondary roads, telecom stations, conveyor control and where automatic control of lighting is required.

Advantages of Twilight Switch

The benefits of a twilight switch are:

It saves energy.
It is easy to install.
It has compact dimensions.
It is cost-friendly.
It has an adjustable light intensity level.
Systems are available for operating over distances from 10–15 mm up to 50 m or more.

Disadvantages of Twilight Switch

The drawbacks of a twilight switch are:

An external sensor is needed.
Unwanted tripping may occur.
Sensors should be kept clean.
For use only in closed, dry rooms (device); the sensor is intended for outdoor installation.