Occupancy and Daylight Control for Lighting

Lighting switches or dims automatically according to occupancy and daylight levels.

How does occupancy and daylight-linked lighting control work?

Lighting control switches and dims lighting automatically according to two variables: occupancy and daylight. Occupancy sensors detect whether people are present in the room and switch off lighting in unused rooms after a hold-off time. Daylight harvesting, or constant illuminance control, measures the available light with a brightness sensor and dims the luminaires just enough to reach the setpoint at the workplace, for example 500 lux to EN 12464-1. When plenty of daylight enters, the luminaires near the windows run at only a fraction of their output. Technically, this is implemented via digital interfaces such as DALI (Digital Addressable Lighting Interface), where each luminaire is individually addressable, or wirelessly via EnOcean. Both sensors can be combined in a single device and integrated into the building automation system.

Which buildings benefit from lighting control?

The prerequisites are DALI- or EnOcean-compatible luminaires or retrofittable actuators; for that reason, dimmable luminaires should be chosen from the outset during an LED conversion. Typical properties are offices, schools, underground car parks, warehouses and circulation areas such as corridors and stairwells, i.e. rooms with variable occupancy or plenty of daylight. Functional rooms with constant lighting requirements, such as operating theatres, are unsuitable. The saving factors according to EN 15193 are 0.3 to 0.5 for offices, 0.5 to 0.7 for warehouses and 0.2 to 0.35 for classrooms.

What does occupancy and daylight-linked control actually deliver?

The control saves 30 to 60 % of lighting electricity, on top of the LED conversion. In offices, 30 to 50 % is realistic compared with manually switched LED lighting; in warehouses and underground car parks up to 70 %. An office building with 32,000 kWh/a of lighting electricity saves around 12,800 kWh/a and 2.0 t CO2/a with the standard factor of 0.4. Costs are €100 to €300 per sensor plus programming; a complete system costs €15 to €30/m². Payback is 3 to 7 years over a 15-year service life. As a side benefit, comfort improves, because brightness and switching state no longer depend on users' attention.

Energy carrier

Strom → Strom

Savings potential

30-60 % Beleuchtungsstrom (zusätzlich zu LED)

Worked example

An office building has already converted its lighting to LED, but the luminaires are still operated manually via wall switches. Lighting electricity is 32,000 kWh/a, because rooms often remain lit at full output even though daylight is sufficient or nobody is present. The operator retrofits DALI occupancy sensors with integrated brightness sensors and sets constant illuminance control to 500 lux at the workplace. For an office, the saving factor of 0.4 is applied according to EN 15193, in the middle of the 0.3 to 0.5 range. The calculation is: 32,000 × 0.4 = 12,800 kWh/a. Lighting electricity therefore falls by around 12,800 kWh/a, which at 0.156 kg CO2/kWh avoids roughly 2.0 t CO2 per year. The saving comes on top of the LED saving already achieved.

Investment & payback

100-300 €/Sensor + Programmierung; Komplettsystem 15-30 €/m² · Service life: 15 a · Payback: 3-7 a

Applicability

Requirements

Exclusion criteria

Typical buildings

Frequently asked questions

How much does daylight and occupancy lighting control save?

Occupancy and daylight-linked control saves 30 to 60 % of lighting electricity, on top of the LED conversion. In offices, 30 to 50 % is realistic, in warehouses and underground car parks up to 70 %, in classrooms 20 to 35 %. An office building with 32,000 kWh/a of lighting electricity saves around 12,800 kWh/a with the standard factor of 0.4.

What is the difference between a motion sensor and an occupancy sensor?

A motion sensor responds to larger movements and is suited to corridors, garages or outdoor areas. An occupancy sensor is considerably more sensitive and also detects small movements such as typing at a desk, so the office lighting does not switch off while someone is working quietly. For workplaces, the occupancy sensor, usually combined with a brightness sensor for constant illuminance control, is therefore the right choice.

How much does DALI lighting control cost?

A DALI occupancy and daylight sensor costs €100 to €300 plus programming and commissioning. For a complete system with sensors, controllers and wiring, allow €15 to €30 per m². With savings of 30 to 60 % of lighting electricity, the control pays back in 3 to 7 years, and the service life is 15 years.

Do you need dimmable LED luminaires for daylight harvesting?

Yes, constant illuminance control requires dimmable luminaires, usually with a DALI driver or alternatively with EnOcean wireless actuators. Non-dimmable luminaires can only be switched on and off, which limits the benefit to occupancy control. Anyone planning an LED conversion should therefore choose DALI-capable luminaires straight away; the extra cost is small and later retrofitting of the control is straightforward.

Which standards govern lighting control in Austria?

ÖNORM EN 15193-1 describes the energy assessment of lighting in buildings and provides the coefficients for occupancy and daylight utilisation from which the saving factor is derived. EN 12464-1 specifies illuminance levels at workplaces, for example 500 lux for office workstations, which the control maintains as the setpoint. Austria's Energy Efficiency Directive Regulation recognises lighting control as an eligible measure.

Related measures

Standards & sources

Metering points in the EDM Toolbox

Mess-Kreis Beleuchtung getrennt + Logging der DALI-Helligkeitssollwerte ergibt aussagekräftige Last-vs-Tageslicht-Kurven.

All measures