Dimmable Profiles and Motion Sensing

Why a profile beats full output all night

Traffic on most roads collapses after the evening peak and stays very low until early morning, so running full output across all of that period spends energy lighting an empty carriageway. The daily load is simply the sum of power multiplied by hours at each step, so the profile is not a cosmetic setting but the number the whole energy system is built around.

The arithmetic of a profile

Take a 60 W luminaire and a ten-hour night. At full output throughout, the daily load is 60 × 10 = 600 Wh. With a three-step profile — four hours at 100%, three at 50% and three at 30% — it becomes (60 × 4) + (30 × 3) + (18 × 3) = 384 Wh, a reduction of 36%. Those are not savings on paper only: at three days of autonomy and 80% depth of discharge, the 600 Wh profile calls for roughly 2,250 Wh of battery nameplate energy, while the 384 Wh profile needs about 1,440 Wh, and the array follows in proportion. The sizing method is set out in battery autonomy sizing.

Setting the steps to the sun, not to a wristwatch

A fixed clock drifts against the seasons: a luminaire that starts at 18:30 lights an empty street in summer and switches on an hour after dusk in winter. Most designs therefore use an astronomical clock that derives sunset from the location’s latitude and longitude and the date, with profile steps defined relative to that event — switch on at sunset, reduce output two hours later, reduce again at a fixed local time, switch off at sunrise. The controller needs the correct coordinates entered and a daylight sensor that is not affected by its own luminaire or by a passing headlight. Both details belong in the commissioning record, since a system with the wrong coordinates behaves oddly all year and gets blamed on the equipment.

Motion sensing: radar, infrared and the settings that matter

A motion sensor lets a luminaire sit at a low standby level and step up to full output when someone enters the detection zone. Microwave radar detects movement by the Doppler shift of reflected signals and works through a sealed cover without an aperture, which suits an enclosed luminaire, but it can see through thin walls and can be triggered by moving vegetation or heavy rain if sensitivity is set too high. Passive infrared sensing responds to changes in infrared radiation and needs a clear optical path, which makes it vulnerable to dirt, condensation and insects on the window, and slow-moving or insulated objects can be missed. Neither technology is universally better: what matters is the specified detection range, the mounting height it was qualified at, immunity to rain and small animals, and whether the unit can hold a vehicle’s approach speed.

Sensor settings and what they do to the battery

• Standby level — output held when nothing is detected; 15% to 30% is typical on a residential or pedestrian route.
• Detection range and zone shape — the distance at which a person or vehicle is detected, and whether the zone covers the carriageway or only a narrow cone below the head.
• Hold time — how long the luminaire stays boosted after the last detection; 20 to 60 seconds is a common range for pedestrians.
• Boost level — usually full output, though some schemes boost only to 70% or 80% to protect battery state of charge in a poor week.
• Night-time window — the period during which sensing is active, so the evening peak stays at full output regardless of detections.

Savings depend entirely on how often the road is used, which is why sensing performs well on a quiet cul-de-sac and disappoints on a distributor road with traffic all night. The peak current draw is unchanged during a boost period, so an undersized battery or an over-long cable will still show voltage sag at the moment of step-up — a fault that looks like a sensor problem but is a system design problem. A savings figure quoted as a percentage is worthless without the assumed trigger rate, so ask the bidder to state the detections per night the calculation assumes.

Specifying a profile that can be verified

The requirement should read as a table of periods, percentages and switching events, plus the sensor settings and the resulting daily energy in watt-hours. Require the controller’s setting sheet at handover and make at least one profile step and the hold time verifiable on site with a light meter and a stopwatch. Because the profile determines the load, it also determines the panel, the battery and the pole’s structural burden, so it should be fixed before the bill of materials is priced rather than adjusted afterwards; the component list it feeds appears in the bill of materials, and the clauses that make it enforceable are described in how to specify solar street lights in a tender.

How we can help

We are a China-based trading and project sourcing company, not a manufacturer. We review specifications and BOQs, match a product and configuration to your site conditions, source from qualified manufacturers, and manage quality through to pre-shipment inspection.

• Convert your lighting hours and traffic pattern into a written dimming profile with a daily energy figure.
• Check that the panel and battery offered match that load with the autonomy you asked for.
• Review sensor type, detection range and hold times against the road’s actual use.
• Require a controller setting sheet at handover so the profile on site matches the profile specified.

If you are preparing a tender or specification and want a second opinion, contact us.