Twilight switch

A dusk-to-dawn switch is a modular DIN-rail device that automatically controls a lighting circuit based on ambient light level. It combines a power relay with an external light sensor and allows fine adjustment of the switching threshold. Unlike an astronomical time switch, which calculates theoretical sunrise and sunset times, it responds to the site's actual light level. Its installation meets the requirements of the NF C 15-100 standard and CE marking.

Operation and differences from the astronomical time switch

Principle of measuring actual light level

Our installation experience confirms that the dusk-to-dawn switch offers greater responsiveness in configurations subject to local light variations. The external light sensor picks up ambient light and sends the information to the DIN-rail module. The switching threshold, expressed in lux, is set according to the application's needs. In the field, we observe that this direct measurement avoids nuisance switching during daytime storms or heavy cloud cover.

Comparison with the astronomical time switch for lighting management

The astronomical time switch calculates day and night times without a light sensor. It suits sites where darkness is predictable and uniform. By contrast, the dusk-to-dawn switch becomes necessary as soon as buildings, dense vegetation or irregular weather conditions disturb natural light levels. Feedback from installers confirms that the choice between the two devices depends on the criticality of the lighting and the geographic environment.

Technical characteristics and compliance

Modular construction and housing materials

The polyamide housing provides satisfactory mechanical strength in an electrical panel and electrical insulation suited to industrial use. DIN-rail mounting standardises integration into distribution panels and enclosures. The external light sensor is positioned wherever best represents ambient light level, sometimes at a distance from the control module.

Applicable standards and CE marking

Compliance with NF C 15-100 guarantees personal safety and correct operation in low-voltage electrical installations. CE marking confirms compliance with the applicable European requirements. We recommend checking that the output rating is compatible with the connected lighting load, particularly for LED installations with a high inrush current.

Typical applications and commissioning feedback

Automatic outdoor lighting and roadway lighting

Our standard practice favours the dusk-to-dawn switch for roadway, car-park and shared-space lighting where safety depends on reliable switching-on at dusk. Automatic management removes the need for manual intervention and reduces consumption linked to forgetting to switch off. Our commissioning tests show that a setting between 10 and 50 lux covers most public and private lighting needs.

Illuminated signs and commercial lighting

Illuminated signs also benefit from this automation to comply with opening hours without relying on rigid time-based programming. We find that combining a dusk-to-dawn switch with a modular contactor allows large loads to be controlled while keeping centralised control. This architecture simplifies maintenance and standardises the behaviour of lighting points across a single site.

Frequently asked questions

What is the fundamental difference between a dusk-to-dawn switch and an astronomical time switch?

The dusk-to-dawn switch measures actual light level via an external sensor and triggers lighting based on the threshold set, whereas the astronomical time switch theoretically calculates sunrise and sunset times without taking local weather conditions into account.

How should the light sensor be positioned for optimal operation?

The sensor should be installed wherever best represents ambient light level, shielded from stray light sources such as nearby floodlights or reflections, and oriented toward the area of sky most exposed to natural variation.

Which light threshold should be set for an outdoor car park?

Our installation feedback shows that a threshold between 10 and 30 lux generally suits outdoor car parks, with a tendency toward lower values for brightly lit urban sites and higher values for rural areas.

Can a dusk-to-dawn switch directly control LED luminaires?

The DIN-rail module generally controls a contactor or power relay; it is worth checking that the output rating supports the load's rated current, taking into account the high inrush currents of some LED power supplies.