How Do Security Lights Work?

For many homes and businesses, security lighting is the first line of defence against trespass and accidents after dusk. When light is cast over driveways, gardens, and entry points upon the detection of movement, these fixtures provide a clear signal to potential intruders that a property is actively monitored.

But how does this technology work, and why is it so important? In this article, we’ll look into the specifics of motion detection and security lights, and the key differences between each energy source sensed. Keep reading to learn more…

Why are security lights so effective?

Security lighting has remained a strong, viable option for many businesses and homeowners because of its ability to remove uncertainty.
By casting light into the cover of darkness, you tip the balance back in your favour, away from unwanted intruders. An illuminated exterior increases the chance of being seen, whether by neighbours, passers-by or CCTV cameras, and makes covert entry far more difficult.

Criminals rarely pick targets under a spotlight, so well-placed floodlights, timers or motion-activated units reduce opportunities for attackers to probe windows, doors, or perimeter fences under cover of night.

Beyond the immediate visual barrier, security lights also help establish a neighbourhood watch mentality. When one property is brightly lit, it raises collective awareness. Neighbours become more alert to movement, discouraging repeat offences in the wider area.

Additionally, security lighting is both cost-effective and low-maintenance. Unlike alarms that rely on occupant response, lights work continuously (or upon demand) to project an aura of occupancy.

How motion sensors work

Motion sensors are devices purpose-built to detect changes in their surroundings, be that light intensity, sound waves, or heat.

A motion sensor is commonly made up of three parts: a sensing module, a control circuit and an output switch.

The sensing module continuously monitors a particular form of energy. These energy forms are:

• Infrared radiation for heat.
• Ultrasonic pulses for sound.
• Microwave emissions for electromagnetic waves.
• A simple infrared beam for active detection.

The control circuit analyses real-time data from the module, comparing it against a stored reference level. A motion sensor relies on sensing a change in stable conditions.

Once the sensor notices these substantive changes (commonly known as a “trigger event”) the control circuit activates the output stage. This may be a solid-state relay or a low-voltage driver for LEDs, though older devices often use mechanical relays to connect mains power.

The light then remains on for a defined period, typically adjustable from a few seconds up to several minutes, before the sensor re-establishes the baseline and turns the lamp off.

Sensitivity settings determine how easily a sensor responds to minor disturbances, allowing for some fine-tuning to avoid false alarms from small animals, wind-blown foliage or passing traffic. Detection range depends on the sensor type and lens design.

Threshold controls (“lux” for light-level sensitivity, and “time” for activation duration) allow homeowners to specify that motion detection only occurs at night or to tailor how long lights remain illuminated.

Motion sensors offer an intelligent activation method for security-lighting systems, providing responsive, energy-efficient illumination exactly when and where it is needed.

What are the different types of motion sensors?

Security lights use a range of sensing technologies to detect movement and activate illumination. As we mentioned earlier, there are four main types of energy forms sensed, but there are five different sensor types. Let’s look at them in more detail:

Passive infrared (PIR) sensors

Passive infrared sensors detect the natural heat energy (also known as infrared radiation) emitted by living bodies.

A PIR unit contains two pyroelectric elements, each monitoring a zone. Under stable conditions, both elements register the same ambient temperature.

When a warm object, such as a person or animal, moves across one zone into the next, the resulting temperature differential generates a small voltage. The sensor recognises this change and triggers the light.

A Fresnel lens array sits over the sensor elements, dividing the field of view into multiple narrow beams. This lens both magnifies infrared wavelengths (typically 8–12 µm for a human body) and extends range.
When an object traverses these beams, the sensor experiences a rapid rise and fall in detected IR energy, indicating motion.

Benefits of PIR sensors:

• Passive operation: emits no energy, so it cannot be seen through glass or walls.
• Good range: typically 8–12 metres with a 90°–120° coverage angle.
• Cost-effective: PIR sensors use low-power, making them the default for domestic floodlights and wall units.

Ultrasonic motion sensors

Ultrasonic sensors emit high-frequency sound waves on a continual basis. These sound waves, usually 40 kHz, are beyond the range of human hearing.

An ultrasonic transducer broadcasts pulses into the detection zone and listens for echoes. When an object moves, it disturbs the time it takes for echoes to return.

The control circuit compares successive echo patterns, noticing any significant changes which signals movement, before switching on the light.

Because sound waves can diffract around corners and through thin partitions, ultrasonic sensors cover complex layouts where line-of-sight may be obstructed.

They can operate in complete darkness and remain unaffected by temperature fluctuations. Ultrasonic sensors are common in automatic doors and indoor security zones, but less so for outdoor lighting due to environmental noise triggers.

Benefits of ultrasonic sensors:

• Active system: continually emits and processes sound pulses.
• Great coverage: up to 20 metres, with wrap-around detection in enclosed spaces.
• Highly sensitive: can detect minor movement, such as slow walking.

Microwave sensors

Operating similarly to ultrasonic motion sensors, microwave detectors instead function on the Doppler-shift principle.

A transmitter emits low-power microwave signals in the 2.4 GHz band into the area under surveillance. Moving objects reflect those waves back, and the receiver compares the frequency of the returned signal to the original. When there are changes in this shift, it indicates motion, thus prompting the sensor to activate the light.

Because microwaves penetrate non-metallic materials, these sensors can “see” through foliage, walls or thin plastic covers, allowing them to excel in large-area coverage and irregular spaces.

They are favoured in high-security or commercial sites where broad coverage and obstacle penetration are priorities.

Benefits of microwave sensors:

• Active system: continuous wave emission like that of ultrasound sensors.
• Great range: up to 15–20 metres, 360° detection possible with appropriate antenna geometry.
• Better visibility: can “see” through things that other sensors cannot.

Active infrared sensors

Active infrared sensors use an emitter and receiver to form an invisible light beam. This narrow beam, typically in the near-infrared spectrum, is continuously shined from the emitter toward a photodiode receiver.

When an object interrupts this beam, the receiver detects a sudden drop in signal and triggers the light.

These systems are great for controlling specific choke points, and are commonly used in garage-door activation, warehouse loading bays, and controlled-entry corridors. However, they are less suitable for open-area monitoring due to line-of-sight requirements.

Benefits of active infrared sensors:

• Accurate in defined zones: any beam interruption counts as motion.
• Immunity: ambient temperature variations and most sources of false heat signatures don’t affect the beam.

Hybrid sensors

Hybrid sensors (also known as dual-technology sensors) combine two detection methods (most commonly PIR and microwave) into a single unit.

Both systems must register motion within a given time window for the light to activate, sharply reducing false alarms.

For example, the PIR circuit monitors thermal changes while the microwave module watches for Doppler shifts. Only when both signals coincide does the control relay close, illuminating the lamp.

This does, however, slightly slow the response time, as both sensors need to process the data. They are also more expensive, and require more complex calibration than single-technology units.

Benefits of hybrid sensors:

• Low false-alarm rate: the dual-technology approach reduces false alarms, making them ideal for high security situations, critical infrastructure perimeters, banks and military sites.

Shop security lighting at Lyco

Now that you understand how security lights and sensors operate, it’s time to take your security up a notch. At Lyco, we have a wide range of security lighting to suit your security needs.

We are the UK’s premier lighting company, providing the latest products from around the world at the very best prices. We are able to dispatch 98% of all orders on the same day they are received.

If you want to know more about our products and services, our team have the knowledge to assist you. Contact us today to learn more.

Shop the best security lights at Lyco today

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