Knowledge base

Electronic Visual Distress Signal Devices (EVDS) are engineered to be seen quickly, clearly, and at distance. Standards such as RTCM 13200.0 exist to verify that a device’s light output, colour, SOS pattern, endurance and environmental robustness are measured objectively, so performance in the field matches performance on paper.

Brightness and Detection

Brightness (candela) determines conspicuity and viewing distance in low-light conditions. RTCM 13200.0 specifies minimum luminous intensity and requires that a compliant EVDS maintains that intensity for its rated operating time under test conditions, verified by photometric measurement.

Colour and Clarity

Colour affects recognition and contrast. RTCM 13200.0 defines chromaticity ranges and a dual-colour SOS pattern (Red/Orange and Cyan) to maximise visibility across sea and sky backgrounds and reduce confusion with navigation or shore lights. Colour output is lab-tested as part of compliance.

SOS Pattern Recognition

The SOS pattern is universally recognised. The standard sets precise timing tolerances so the sequence is consistent across the full runtime, avoiding irregular flashes that could delay interpretation by lookouts or search teams.

Optics and Light Spread

Optical design, lenses, diffusers and reflectors, controls distribution. Many EVDS provide 360° horizontal coverage with defined vertical spread to ensure visibility from varying observer heights and sea states. Even distribution prevents hotspots and dead zones that reduce effective conspicuity.

Runtime and Reliability

Endurance matters during extended searches. Battery chemistry, temperature and duty cycle affect duration. RTCM testing verifies that brightness and pattern remain within specification over the stated runtime using the specified power source.

Environmental Endurance

Real-world conditions include immersion, vibration, salt spray and temperature extremes. Compliance testing confirms the device functions correctly after environmental exposure. Always check ingress protection (IP) rating and the recommended operating temperature range.

Human Vision Factors

At night, vision operates in mesopic conditions (between photopic and scotopic), where contrast and colour perception change. Balanced intensity, defined colour bands and a regular flash pattern improve detection without excessive glare. Simple, glove-friendly activation reduces user error under stress.

Best Practice

• Keep the device upright, unobstructed and above spray when possible.
• Use the defined SOS mode specified by the manufacturer.
• Clean the lens periodically to maintain optical efficiency.
• Replace batteries on schedule and after extended use.
• Function-test in line with the operating instructions.

Summary: Choose an EVDS with documented conformance to RTCM 13200.0, verified candela and colour measurements, a precise SOS pattern and proven endurance in environmental tests. This combination delivers predictable, high-visibility signalling when time and clarity matter most.