Smart Lighting Control via BMS: Occupancy Sensors, Daylight Harvesting & Energy Savings

Lighting represents 20–30% of electricity consumption in a typical Bangladesh commercial building. In a busy Dhaka office complex spending BDT 20 lakh per month on electricity, that means BDT 4–6 lakh is going directly to lighting — much of it illuminating empty corridors, unoccupied meeting rooms, and perimeter zones already bathed in natural daylight from floor-to-ceiling windows.

Smart lighting control, integrated into your Building Management System (BMS), addresses this waste systematically. By combining the DALI protocol for digital lighting control, occupancy sensors that detect when spaces are in use, daylight harvesting systems that dim artificial lights when natural light is sufficient, and time-based scheduling coordinated with building occupancy, a BMS-integrated lighting system can reduce lighting energy consumption by 30–60% — without any impact on occupant comfort or productivity.

This article explains each element of smart lighting control and how they work together within a BMS architecture.

Why Lighting Integration Belongs in the BMS

Lighting control and HVAC control are not independent problems. They are deeply interrelated. Lighting generates heat — a standard 100W luminaire adds 100W of heat to the space it illuminates, which the HVAC system must then remove. Reducing lighting power through dimming or switching off therefore has a double benefit: direct energy savings on the lighting circuit and indirect savings on the HVAC cooling load.

A BMS that controls both lighting and HVAC can optimise them together. When a zone occupancy sensor detects that a space is empty, the BMS simultaneously turns off the lights and reduces the cooling output to that zone — a coordinated response that captures both lighting and HVAC savings. A standalone lighting control system operating independently cannot achieve this coordination.

LEED v4's Indoor Environmental Quality (IEQ) credits also reward lighting controllability — the ability for occupants to adjust lighting to meet their individual needs. A BMS-integrated lighting system with zone-level control satisfies this requirement while also delivering energy savings.

DALI: The Protocol That Makes BMS Lighting Integration Work

DALI — Digital Addressable Lighting Interface — is the international standard protocol for controlling lighting within a building automation environment. Defined in IEC 62386, DALI allows a BMS controller to communicate individually with each DALI-addressed luminaire, providing precise digital commands for on/off switching and continuous dimming from 0.1% to 100% of full output.

How DALI Works

A DALI system consists of DALI controllers (devices that send commands), DALI drivers (electronic ballasts or LED drivers inside each luminaire that receive and execute commands), and the DALI two-wire bus that connects them. Up to 64 individually addressed devices can exist on a single DALI segment, and multiple segments can be connected to a single BMS controller through DALI gateways.

Each DALI device has a unique address (0–63) and can also be assigned to one or more DALI groups (up to 16 groups per segment). Groups allow the BMS to command multiple luminaires simultaneously — dimming all luminaires in a conference room, for instance — without sending individual commands to each fixture.

DALI supports 16 pre-programmed scene settings per device. A "meeting" scene might dim corridor lights to 30% while bringing the meeting room to 500 lux. A "cleaning" scene might bring all luminaires to 100% for the facility team's evening round. A "presentation" scene dims the front zone of a conference room to allow screen visibility. The BMS triggers these scenes through scheduled events, occupancy inputs, or manual commands.

DALI vs. 0-10V Dimming

An older alternative to DALI is 0-10V analogue dimming, where a control voltage of 0–10V commands the dimming level. While 0-10V is simpler and less expensive, it lacks DALI's addressability — all luminaires connected to the same 0-10V control wire dim together, with no individual device control. DALI provides far greater flexibility and is the recommended choice for new BMS-integrated lighting installations.

Integration with BMS

DALI integrates with the BMS through DALI gateways — devices that translate between DALI commands and the BMS communication protocol (typically BACnet or Modbus). The gateway exposes each DALI device as a BMS object: the BMS can read the current output level, command a new level, read fault status (lamp failure, driver failure), and trigger scene changes, all through standard BMS software objects.

Occupancy Sensors: Turning Off What Nobody Is Using

The most straightforward energy saving in any building is turning off lights when a space is empty. Occupancy sensors make this automatic, eliminating dependence on occupants remembering to switch off lights when they leave.

Sensor Technologies

Passive Infrared (PIR) sensors detect the heat signature of moving people against the thermal background of the room. They are highly reliable in small spaces — private offices, meeting rooms, toilets — where the occupant moves regularly enough to maintain detection. PIR sensors are economical and consume very low power. Their limitation is that they cannot detect a stationary occupant — a person sitting quietly reading may "time out" the sensor and cause the lights to switch off.

Ultrasonic sensors emit high-frequency sound waves and detect movement through Doppler shift — the change in return frequency caused by movement. They can detect very subtle movements, including minor hand motions, and work well in spaces where PIR sensors might produce false "unoccupied" reads. Ultrasonic sensors work effectively in spaces with irregular shapes or obstructions.

Dual-technology sensors combine PIR and ultrasonic detection and are the premium choice for occupied workspaces. They switch on when either technology detects occupancy and switch off only when both technologies simultaneously indicate vacancy. This dual-confirmation approach virtually eliminates the nuisance switching that frustrates occupants when they experience lights switching off while they are still present.

Camera-based occupancy counting systems use video analytics to count the number of people in a space. These provide richer occupancy data than simple occupied/unoccupied binary signals — the BMS can use the actual occupancy count to modulate both lighting level and ventilation rate. These are particularly valuable in large open spaces, cafeterias, and lobbies.

Vacancy vs. Occupancy Sensing

LEED (and ASHRAE 90.1 in certain occupancy types) distinguishes between occupancy sensing (automatic on and automatic off) and vacancy sensing (manual on and automatic off). Vacancy sensing gives occupants control over switching lights on — which reduces the false-on events that occur when someone briefly enters a space without needing lighting — while still automatically switching lights off when the space is vacated. ASHRAE 90.1 requires vacancy sensing in private offices, storage areas, and certain other occupancy types.

The BMS accommodates both modes: the scene trigger from an occupancy sensor can be set to automatically bring lights to full output (occupancy mode) or to a low "announce" level with full control returned to the manual switch (vacancy mode).

Sensor Placement

Correct sensor placement is critical. A PIR sensor in a private office should be positioned to cover the entire floor area of the occupied zone, typically ceiling-mounted at the centre of the room or pointing toward the desk area. In an open-plan office, sensors are positioned to avoid "blind spots" behind partitions and to ensure that the combination of sensor coverage zones covers every workstation.

The BMS integrator works with the lighting designer and architect during the design phase to determine sensor positions that provide complete coverage without interference from HVAC air supply (which can cause false triggers on ultrasonic sensors) or direct sunlight (which can blind PIR sensors).

Daylight Harvesting: Using Free Light Intelligently

Bangladesh receives abundant solar radiation throughout the year. On a clear Dhaka day, the outdoor illuminance at noon can exceed 100,000 lux. Even allowing for window glass transmission and interior geometry, the illuminance at a workstation 2–3 metres from a window can be 500–1,000 lux — well above the 300–500 lux typically specified for office work.

Daylight harvesting uses photosensors (also called photocells or daylight sensors) to measure the actual illuminance level in a zone and dims the artificial lighting automatically to maintain the target illuminance while using as much natural daylight as possible.

How Photosensors Work

A photosensor is mounted in the ceiling or wall of the zone it monitors, positioned to measure the illuminance at the working plane — typically simulated by a cosine-corrected sensor that measures downward-directed light. The BMS reads the photosensor signal (typically 0-10V or DALI) and compares it to the target illuminance.

If the photosensor reads 400 lux and the target is 300 lux, the BMS dims the artificial luminaires until the total illuminance (daylight plus artificial) approaches the target. If a cloud passes and the daylight drops to 100 lux, the BMS increases artificial light output to compensate. The occupants experience constant illuminance at their workstations — they are typically unaware of the automatic adjustments happening above them.

Closed-Loop vs. Open-Loop Control

Closed-loop daylight harvesting measures illuminance at the task plane and adjusts artificial lighting to maintain a fixed target. This is the more precise and energy-efficient approach but requires careful sensor placement and commissioning.

Open-loop daylight harvesting measures the illuminance of the incoming daylight (from a sensor that measures only outdoor or perimeter light, not total task plane illuminance) and dims artificial lighting proportionally. This is simpler to implement and commission but relies on a fixed relationship between the measured light and the actual task illuminance — which may not hold perfectly under all conditions.

For most Bangladesh commercial office installations, closed-loop daylight harvesting in the perimeter zone (the first 3–5 metres from the building facade) and open-loop or occupancy-based control in the interior zone provides an effective and practical combination.

Daylight Harvesting Savings

The energy saving from daylight harvesting depends on building orientation, window-to-wall ratio, glazing transmission, occupancy hours, and the local solar profile. In Dhaka's tropical climate, with high solar intensity for most of the year and a standard 08:00–18:00 office day:

• Perimeter zones (within 4 metres of windows) can achieve 50–70% artificial lighting energy reduction during daylight hours
• Mid-depth zones (4–8 metres from windows) can achieve 20–40% reduction during peak daylight periods
• Core zones (beyond 8 metres, or in buildings with limited fenestration) benefit primarily from occupancy sensing

Across a typical floor plate in a Dhaka office building with generous perimeter glazing, combined occupancy sensing and daylight harvesting reduces lighting energy by 35–55% compared to a conventionally switched, fixed-output lighting installation.

Scheduling: Time-Based Control for Predictable Spaces

Not every space requires occupancy sensing. In predictable environments — building lobbies, car parks, plant rooms, stairwells — time-based schedules are sufficient and more cost-effective. The BMS schedules these areas to shift to lower output or switch off during unoccupied hours: car park lighting at 20% from midnight to 6 AM, lobby lighting at 30% after 10 PM, stairwell lighting at 50% outside core hours.

Astronomical Clock

An astronomical clock function in the BMS automatically calculates sunrise and sunset times for Dhaka's latitude (23.8°N) and adjusts outdoor and perimeter lighting schedules accordingly. Exterior façade lighting, car park entrance lighting, and security perimeter lighting switch on at sunset and off at sunrise — without the facility manager needing to manually update schedules as day length changes through the seasons.

Scene Management for Meeting Rooms and Lobbies

Meeting rooms benefit from pre-programmed lighting scenes that optimise the environment for different activities without requiring occupants to understand the lighting control system. A single button press or an event triggered from the room booking system switches the room between "Presentation" mode (low front illuminance, high side illuminance for the audience), "Conference" mode (uniform 400 lux throughout), and "Standby" mode (10% output, sufficient for a quick glance into the room but minimal energy consumption).

For hotel lobbies, executive boardrooms, and reception areas in Bangladesh's premium commercial buildings, scene management delivered through DALI via the BMS provides the sophisticated ambience control that tenants and guests expect, while still optimising energy consumption when spaces are empty or partially occupied.

Energy Savings Potential: Summarised

For a Dhaka commercial building spending BDT 4 lakh per month on lighting, achieving 40% savings represents BDT 1.6 lakh per month — BDT 19.2 lakh per year. At a typical Bangladesh BMS lighting control project cost of BDT 15–25 lakh for a 10,000 m² building, the simple payback is 1–1.5 years.

Implementation: What to Expect from a Smart Lighting Control Project

A BMS-integrated smart lighting control project proceeds through design, installation, and commissioning phases. During design, the lighting control consultant and BMS engineer agree on sensor locations, DALI addressing, scene programming, and integration points. During installation, DALI wiring is run alongside power wiring (DALI is a low-voltage signal circuit), sensors are mounted and connected, and DALI addresses are assigned to each driver.

Commissioning of the lighting control system includes sensor sensitivity adjustment, time-out delay setting, scene level programming, and most critically, daylight harvesting calibration. Calibration requires testing under a range of daylight conditions — full sun, overcast, dawn — and adjusting sensor gains and control loops until the system maintains consistent task plane illuminance under all conditions. Proper commissioning is the difference between a smart lighting system that occupants praise and one they fight with.

SSAL's commissioning team has the tools and experience to commission DALI-based lighting control systems correctly, including the integration with BMS supervisory software for energy reporting and alarm monitoring.

Upgrade Your Building's Lighting Intelligence Today

Whether you are specifying a new commercial development, retrofitting an existing building, or planning a lighting upgrade in conjunction with an LED luminaire replacement project, BMS-integrated smart lighting control delivers measurable energy savings and occupant satisfaction improvements.

Get Free Consultation — Contact SSAL to discuss smart lighting control options for your building. Our team can assess your current installation, identify saving opportunities, and recommend a solution appropriate for your budget and building type.