What is a visual signal?

An industrial visual signal is a light-emitting device enclosed within a colored or clear lens, designed to provide immediate visual indication of system status, warnings, or hazardous conditions. Visual signals are commonly used across industrial, commercial, and hazardous locations and are frequently deployed as a supplement to audible alarms to improve situational awareness.

Unlike general-purpose luminaires, visual signaling devices are engineered specifically to attract attention, not to illuminate workspaces.

Visual signal effectiveness and light intensity

With the exception of basic status indicators, the primary function of an industrial beacon or visual alarm is rapid detection by personnel. As such, effective luminous intensity, rather than total illumination, is the most critical performance metric.

Different light source technologies vary widely in their ability to attract attention, particularly in flashing modes. Devices with high illumination capability may still perform poorly as warning signals. Therefore, measured effective candela (cd) is the preferred basis for evaluating and comparing visual signal performance.

Our partner, E2S Warning Signals, a global leader in industrial visual signals, provides instrumented data obtained through direct measurement. All published values are derived from actual testing of fully assembled devices and are not based solely on theoretical calculations or industry assumptions, ensuring accurate and repeatable product comparison.

Visual signal light source technologies

Incandescent / Filament lamps

Incandescent visual signals can operate in steady or flashing modes using external control circuitry. These lamps offer moderate light output at low initial cost and may be enhanced using Fresnel lenses. However, filament-based devices have limited service life and are particularly susceptible to vibration-related failures.

Halogen lamps

Halogen lamps are a refinement of incandescent technology, operating at higher filament temperatures within a halogen gas envelope.

Benefits include:

• Increased luminous efficiency
• Extended lamp life (up to three times longer than standard incandescent lamps)

For example, a 40W halogen lamp can provide up to 80% greater luminous efficiency (lumens per watt) compared to a conventional incandescent lamp.

Xenon strobe beacons

Xenon strobes operate using high-voltage energy supplied by an internal inverter circuit. Upon activation, the xenon tube produces a high-intensity, short-duration flash, making this technology highly effective for industrial warning and alarm applications.

Key performance characteristics:

• Light output depends on tube size, capacitor energy, and operating voltage
• Typical service life ranges from 5 to 8 million flashes
• Gradual degradation of light output prior to end-of-life failure

Xenon strobes remain one of the most effective technologies for long-range visual warning signals.

Light Emitting Diode (LED) visual signals

LEDs are semiconductor devices that emit a single wavelength (color) determined by material composition. While LEDs typically do not match xenon strobes in peak intensity, they provide:

• Extremely low power consumption
• Long operational life
• High resistance to shock and vibration

LED visual signals are widely used for status indication, continuous signaling, and low-maintenance applications.

Measurement of visual signal output (Effective Candela)

E2S Warning Signals measures visual signal performance using a spectrometer to determine the average effective luminous intensity of the complete beacon assembly, including lens and enclosure. Results are expressed as Effective Candela (cd).

Effective luminous intensity (Effective Candela – cd) using instrumented photometric measurement

A spectrometer-based photometric measurement system is used to capture the average luminous intensity across the entire beacon lens. Measurements are performed on fully assembled production units fitted with a clear lens, ensuring results reflect real-world performance rather than component-level assumptions.

The collected photometric data is mathematically processed and converted into an Effective Candela (cd) value, representing the perceived steady-state brightness of the signal to a human observer.

Where:

• I(t) is the instantaneous value in candela (cd)
• a is the visual time constant (0.2 nighttime, 0.1 daytime)
• t2 − t1 is the pulse duration measured between 10% peak amplitude points

Measured vs calculated light output in xenon strobes

Historically, xenon strobe performance has often been estimated using joule-based calculations. These methods frequently overstate real-world performance, particularly peak candela values.

Actual visual effectiveness is influenced by:

• Lens design and efficiency
• Lens color
• Flash tube geometry and placement
• Optical losses within the enclosure

As a result, calculated values alone are not suitable for accurate comparison between visual signaling devices.

E2S Performance Reporting

E2S publishes two measured values for xenon strobes obtained from fully assembled units with clear lenses:

• Effective Candela (Measured)
  • Represents perceived steady-state intensity
  • Primary metric for comparing visual signal performance
• Peak Candela (Measured)
  • Maximum instantaneous output during a flash
  • Not recommended for comparative evaluation

Calculated joule-based values are provided for reference only and should not be used for performance comparison.

The visual signaling devices shown below are all 5-joule, energy-rated xenon strobes. Although they share the same energy rating, they differ significantly in mechanical enclosure design and optical lens configuration.  Table 2 highlights the anomalies and underlying assumptions that can introduce substantial inaccuracies when effective candela is calculated or estimated using a rule-of-thumb approach, rather than being empirically measured under controlled conditions.

Table 1: Comparison of Measured effective candela with Calculated effective candela: Three different 5 Joule E2S beacons.

This example clearly demonstrates why measured effective candela must be used when specifying or comparing visual signaling devices.

Beacon effectiveness & range

A common question in visual signaling system design is the effective range of a given device. The effective candela (also referred to as effective candlepower) can be used to determine this range by applying the formula referenced in EN 54-23 and the Illuminating Engineering Society of North America (IES) Lighting Handbook, Fifth Edition.  The formula below converts effective candela into effective warning distance, representing the distance at which a visual signal provides an alerting function, rather than serving solely as an informational indicator.

Where: Ieff(av) = Effective Candela,  d = Distance (m)

The formula below may be used to convert effective candela into viewing distance or range, based on normal visibility in day time conditions.

Where: Ieff(av) = Effective Candela,  d = Distance (feet), Lb = Foot-Lamberts background illuminance (normal day time conditions, Lb = 2919 ft-L)

From the above two formulas the table below gives an indication of both warning distance and range of a visual signal given an effective candela measurement.

Table 2: Indication of warning distance and range of a visual signal given an effective candela measurement.

Example: Performance Variability in 5-joule xenon beacons

Although multiple beacons may share the same energy rating, actual effectiveness varies significantly due to optical and mechanical design differences.

Impact of lens color on light output

• Clear: 100%
• Yellow: 85%
• Amber: 59%
• Green: 51%
• Magenta: 34%
• Blue: 27%
• Red: 15%

All information presented is intended for reference and guidance only and should not be relied upon as a guarantee of performance, coverage area, or system effectiveness.

Installation and application considerations

• Ensure unobstructed omnidirectional light output where required
• Allow sufficient airflow to prevent thermal buildup
• Avoid excessive vibration, particularly with filament-based devices
• Position visual signals within the direct line of sight of personnel
• Audible alarms should remain the primary alert mechanism, with visual signals used for reinforcement or status indication

Visual signal color coding

Visual signal colors are aligned with IEC 60073 and harmonized with ANSI Z535.1 and NFPA 79:

• Red — Danger / Emergency
• Amber (Yellow) — Warning / Abnormal condition
• Green — Normal or safe condition
• Blue — Mandatory or site-defined function
• Clear (White) — Status indication only

Explore The Signal Source’s range of visual signals

• Strobes
• Combined audio-visual signals