Optical and acoustic signalling
Optical and acoustic signalling
Visual and acoustic signals are used to inform users. Signal lamps, signal towers and acoustic signals have an important safety function: they warn users and operators in dangerous situations and provide information about the status of the machine.
Status lights are often installed on equipment in industrial production and process control environments. Acoustic signals are an indispensable addition to visual warnings in this context. In environments with limited visibility or high ambient noise, audible signals ensure that warnings do not go unnoticed. Combining light and sound signals increases the likelihood that operators will respond quickly to malfunctions, emergencies or process changes. This significantly improves safety and business continuity.
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The importance of optical and acoustic signalling in industrial environments
Employers are legally responsible for ensuring a safe working environment for their employees and contractors. The use of optical and acoustic signalling is therefore a requirement in situations where risks to people or machinery may arise.
Optical (visual) and acoustic (sound) signalling is used to warn personnel in good time in the event of dangerous situations, process deviations or malfunctions. The aim is to immediately inform the operator or bystanders of an unsafe situation or imminent danger so that swift and appropriate action can be taken. This reduces the risk of injury, material damage or production downtime.
Such signals are widely used on industrial machines, process installations and control panels, as well as in emergency and evacuation systems. Their use and implementation are laid down in various European directives and standards, such as the Machinery Directive and standards such as EN ISO 7731 (acoustic signals) and EN 981 / EN ISO 7010 (visual signals). These stipulate that signals must be clear, unambiguous and easily perceptible, even in noisy or poorly lit environments.
The basic principle of effective signalling is that it must be reliable and fault-tolerant: a single defect or malfunction must not lead to the loss of the safety function. For this reason, fail-safe systems are often used in practice, for example a combination of flashing lights and audible signals.
Application examples for optical and acoustic signalling technologies
Optical and acoustic signalling is used in virtually all industrial sectors to improve safety, process continuity and situational awareness. The choice of the right type of signalling depends on the environment, the noise level, the lighting conditions and the nature of the process.
In production environments, signal towers and status lights are used to clearly indicate the status of machines or production lines. Typical statuses include ‘operation’, ‘malfunction’, ‘maintenance’ or ‘danger’. Clear and standardised signalling enables operators to respond more quickly and minimise downtime.
Flashing lights and sirens for process plants and the chemical industry
In process installations and the (petro)chemical sector, flashing lights, horns and sirens serve as critical warnings in the event of pressure build-up, leaks, overheating or other process deviations. The combination of visual and acoustic signals ensures high detectability, even in complex or noisy installations.
Light and sound signals in logistics and warehouse environments
In logistics environments, warehouses and loading bays, light signals and acoustic warnings are used to signal collision hazards or vehicle movements. Examples include warnings for forklift trucks, automatic doors, AGVs or docking stations. This increases safety in busy workspaces with heavy traffic.
Optical-acoustic alarms for emergencies and evacuation
Combined optical-acoustic alarm systems are used in the event of fire, gas detection or other emergencies. These alarm signals are designed to warn people quickly and effectively, even in poor visibility or high background noise. This significantly increases evacuation reliability.
ATEX-certified signalling for potentially explosive atmospheres
In potentially explosive atmospheres (ATEX zones), specially certified signalling devices that comply with Directive 2014/34/EU are used. These components are designed not to form an ignition source in the presence of flammable gases or dust. This ensures that the system remains safe within the requirements for Zones 1, 2, 21 and 22.
By correctly selecting and installing signalling devices in accordance with the applicable standards, an installation can not only be made safer, but also comply with the requirements for CE marking and occupational safety.
Standards, installation and CE requirements for industrial signalling
By correctly selecting and installing signalling devices in accordance with the applicable standards, an installation can not only be made safer, but also comply with the requirements for CE marking and occupational safety.
Frequently asked question on optical and acoustic signalling
Optical and acoustic signalling uses visual signals (such as signal lamps, strobe lights and signal towers) and audible signals (such as buzzers, horns or sirens) to quickly inform people about machine status, faults or hazardous situations. In industrial environments, these signals help operators and bystanders recognize abnormal or unsafe conditions in time and take appropriate action, reducing the risk of injury, damage and production downtime. Standards such as EN ISO 7731 and EN 981 describe principles for clear and unambiguous signaling.
Optical signalling communicates information through light, using colour, flashing patterns and visibility. Acoustic signalling communicates information through sound, using tone, pulse and sound pressure level. Visual signals are effective when there is a clear line of sight, while audible signals are essential when operators are not directly observing the machine or when visibility is limited. In practice, both forms of signalling are complementary.
Combining optical and acoustic signals increases the probability of detection. If a warning is missed due to background noise, distraction or poor visibility, the other signalling channel may still be perceived. A combined approach also helps prevent misinterpretation by clearly distinguishing different levels of urgency, as described in EN 981.
Visual signalling alone is often insufficient when:
- sight lines are obstructed by guards, structures or distance;
- operators are moving and not continuously watching the machine;
- ambient conditions such as glare, smoke or dust reduce visibility;
- warnings must reach people outside the immediate visual area.
In such situations, acoustic signalling provides an essential additional warning channel.
There is no single rule stating that optical and acoustic signalling is always mandatory. However, employers have a duty of care to ensure a safe working environment. In practice, the need for signalling is determined by the risk assessment and by requirements related to machine safety and CE conformity. Within the EU, the Machinery Regulation (EU) 2023/1230, applicable from 20 January 2027, sets essential health and safety requirements that may require appropriate warning and signalling measures.
Industrial warning signals must be clearly perceptible, unambiguous and distinguishable from background noise or light. ISO 7731 provides design principles and test methods to ensure audible danger signals can be reliably detected and recognised. EN 981 gives guidance on structuring visual and acoustic danger and information signals according to urgency. For standardised visual safety information such as safety signs and symbols, ISO 7010 is applicable.
Selection should be based on the risk assessment and environmental conditions:
Define what needs to be communicated (status, warning or alarm) and the required urgency.
Assess ambient noise levels, visibility, lighting conditions, distance and use of PPE.
Select suitable signal types, such as steady light or strobe light, and appropriate sound characteristics.
In safety-critical situations, consider combining optical and acoustic signalling to reduce the risk of missed warnings.
A strobe light is typically used when maximum attention is required, such as during alarm situations, in poor visibility, over long viewing distances or in environments with significant visual distraction. A steady light is more suitable for machine status indication, such as “operation”, “standby” or “maintenance”, as it is less intrusive and helps prevent alarm fatigue.
Multifunctional signal lamps are devices capable of displaying multiple colours and/or flashing patterns, allowing a single unit to communicate different machine states or warnings. They are commonly used on machines, production lines and control panels to provide clear and consistent information, such as normal operation, deviation, fault or alarm.
LED signal lamps are widely used because they are energy-efficient and can produce clear, well-defined colours and light intensities for status and warning indication. They respond quickly and are well suited to applications where multiple visual signal states must be communicated. Specific performance characteristics depend on the selected product and the application.
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