reterminal-dm4/emmc-provisioning/docs/SCREEN-BRIGHTNESS-REGULATIONS.md

Screen Brightness — Maritime Regulations and References

This document summarises the international regulations and standards that apply to display brightness and dimming on ship bridges, and how the screen-brightness daemon on the reTerminal DM is aligned with them. It is intended for vessel operators, integrators, and auditors.

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1. Overview

Bridge equipment that presents navigation-related or alarm information on a display is subject to:

• IMO (International Maritime Organization) resolutions, which set performance standards.
• IEC (International Electrotechnical Commission) and IHO (International Hydrographic Organization) standards, which give technical and test requirements.

The reTerminal DM screen-brightness daemon implements behaviour that satisfies the relevant clauses for:

• Adjustable brightness that is never extinguished (“not to extinction”).
• A navigator-resettable brightness/contrast preset (override).
• High luminous intensity for alarm/alert states.
• Night mode that does not degrade crew night vision.
• Three operating modes (NIGHT / DUSK / DAY) consistent with ECDIS-type display practice.

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2. IMO MSC.191(79) — Navigational displays

Full title:
Performance Standards for the Presentation of Navigation-Related Information on Shipborne Navigational Displays

Adoption: 6 December 2004

Applicability: Displays that present navigation-related information on the bridge (including ECDIS and other navigational displays). Often referenced for equipment installed after 1 July 2008.

Source (external):

• imorules.com – MSC.191(79)
• IMO official: MSC.191(79) in the IMO Publications catalogue.

2.1 §8.1 Display adjustment

Requirement	Text (summary)	Implementation in screen-brightness
Adjustability	Contrast and brightness shall be adjustable as applicable to the display technology.	Brightness is controlled in steps 1–5 from ambient sensor and/or override.
Dimming	The display shall be capable of being dimmed.	NIGHT and DUSK modes set low backlight levels (1–2).
Legibility	The range of control shall allow the display to be legible under all ambient light conditions.	Lux thresholds map to levels 1–5 so the display remains usable from night to bright day.
Not to extinction	Implicit in “dimmed” and “legible under all conditions”: the display must not be turned off.	Level 0 is never used. Minimum level is 1 (“not to extinction”).

2.2 §8.1.2 Preset / default

Requirement	Text (summary)	Implementation in screen-brightness
Reset to preset	The navigator shall be able to reset contrast and/or brightness to a preset or default condition.	Override file: echo <1–5> | sudo tee /run/screen-brightness/override sets a fixed level; echo auto restores automatic (ambient + buzzer) behaviour.

Reference (section 8.1):

• imorules.com – 8.1 Display adjustment

2.3 Position of the brightness control

MSC.191(79), MSC.302(87), IHO S-52, and IEC 62288 do not specify where the brightness (or contrast) control must be located on the screen or in the user interface. They only require that:

• Brightness be adjustable and dimmable.
• The navigator be able to reset to a preset or default.

So the position of the brightness control (e.g. bottom-right overlay icon on the reTerminal DM) is an implementation and design choice, not a regulatory requirement. Placement can follow human-factors or vessel-specific guidelines (e.g. readily accessible, non-intrusive) as long as the above requirements are met.

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3. IMO MSC.302(87) — Bridge alert management

Full title:
Adoption of Performance Standards for Bridge Alert Management

Adoption: 17 May 2010

Applicability: Bridge Alert Management (BAM) and presentation of alerts on the bridge. Recommended for central alert management (CAM) and CAM human-machine interface (CAM-HMI) installed on or after 1 July 2014.

Source (external):

• imorules.com – MSC.302(87)
• IMO official: MSC.302(87) PDF in IMO Knowledge Centre.

3.1 Visual alarms and night vision

Requirement	Text (summary)	Implementation in screen-brightness
Night vision	Visual alarms and indicators shall not interfere with night vision.	In ambient mode, NIGHT/DUSK use low levels (1–2); transitions are smooth (one step per poll) to avoid sudden bright flashes.
Dimming not to extinction	Dimming facilities shall be incorporated, though not to extinction.	Same as MSC.191(79): level 0 is never used; minimum is level 1.
High luminous intensity for alerts	Supplemental visual indicators (e.g. for alarms) shall be of high luminous intensity.	When the buzzer is ON (alarm), backlight is set to level 5 (maximum) immediately, with no smooth stepping.
Persistence after alarm	Alerts must remain visible/audible long enough for crew response.	After the buzzer stops, brightness is held at level 5 for a cooldown period (default 10 s), then stepped down; duration is configurable in /etc/screen-brightness.conf.

Reference:

• IMO MSC.302(87) Annex — Performance Standards for Bridge Alert Management (Modules A–D).
• imorules.com – MSC.302(87) Annex

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4. IHO S-52 and IEC 62288 — ECDIS and display presentation

IHO S-52 (International Hydrographic Organization) specifies chart content and display aspects for ECDIS, including colour and luminance behaviour. IEC 62288 implements and tests these and related IMO requirements for shipborne navigational displays.

4.1 Three colour / luminance modes

Mode	Typical use	Implementation in screen-brightness
Day	Bright ambient; high contrast.	DAY-DIM, DAY-NORMAL, DAY-BRIGHT (levels 3–5) by lux bands.
Dusk/Dawn	Transition; reduced luminance.	DUSK mode → level 2.
Night	Low luminance so as not to affect the mariner’s night vision.	NIGHT mode → level 1 (minimum).

IHO S-52 (e.g. Edition 6.1.1):

• “The ambient lighting on the bridge varies between the extremes of bright sunlight … and night, when the light emitted by the display has to be low enough that it does not affect the mariner's night vision.”
• Three colour/luminance modes (day, dusk/dawn, night) are defined for ECDIS; the screen-brightness daemon provides a compatible three-mode luminance framework (NIGHT / DUSK / DAY-*).

IEC 62288 (e.g. IEC 62288:2021):

• General requirements, test methods, and required results for the presentation of navigation-related information on shipborne navigational displays.
• Supports IMO MSC.191(79) and MSC.302(87).
• Full luminance limits (e.g. numerical cd/m² for night) are in the purchased standard; the daemon’s “minimum level 1” and “never 0” satisfy the “dimmed but not to extinction” and “night vision” intent.

Sources (external):

• IHO S-52 — Specifications for chart content and display aspects of ECDIS (IHO publication).
• IEC 62288:2021 — Maritime navigation and radiocommunication equipment and systems – Presentation of navigation-related information on shipborne navigational displays.

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5. Summary table — Regulation vs implementation

Regulation	Clause / topic	Daemon behaviour
MSC.191(79)	§8.1.1 Brightness adjustable, dimmable	Levels 1–5 from ambient sensor; configurable lux→level mapping.
MSC.191(79)	§8.1.1 Legible in all ambient conditions	NIGHT / DUSK / DAY-* modes with configurable lux thresholds.
MSC.191(79)	§8.1.1 Not to extinction	Level 0 never used; minimum level 1.
MSC.191(79)	§8.1.2 Reset to preset	Override file: fixed level 1–5 or auto.
MSC.302(87)	Visual alarms high luminance	Buzzer ON → immediate level 5.
MSC.302(87)	Dimming not to extinction	Same as above; min level 1.
MSC.302(87)	Night vision not degraded	NIGHT/DUSK low levels; smooth stepping on transitions.
MSC.302(87)	Alert persistence	Cooldown (e.g. 10 s) at level 5 after buzzer stops.
IHO S-52 / IEC 62288	Three modes (day / dusk / night)	NIGHT, DUSK, DAY-DIM, DAY-NORMAL, DAY-BRIGHT.
IHO S-52	Night luminance low for night vision	NIGHT mode → level 1.

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6. Configuration and audit

• Config file: /etc/screen-brightness.conf — lux thresholds, levels per mode, cooldown, hysteresis.
• Override (preset): /run/screen-brightness/override — navigator preset (1–5 or auto).
• State (read-only): /run/screen-brightness/state — current mode, level, lux, buzzer, override.
• Reload: systemctl reload screen-brightness (no restart).

For vessel-specific tuning or audits, adjust thresholds and levels in /etc/screen-brightness.conf and document the chosen values and the fact that level 0 is never used.

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7. References (URLs and documents)

Reference	Description	URL or source
IMO MSC.191(79)	Performance standards for presentation of navigation-related information on shipborne navigational displays	https://www.imorules.com/MSCRES_191.79.html
IMO MSC.191(79) §8.1	Display adjustment (brightness, dimming, preset)	https://www.imorules.com/GUID-6B14EB44-F913-4C8F-8E36-F74CE6E8E3DE.html
IMO MSC.302(87)	Performance standards for Bridge Alert Management	https://www.imorules.com/MSCRES_302.87.html
IMO MSC.302(87) Annex	BAM performance standards (Modules A–D)	https://www.imorules.com/MSCRES_302.87_ANN.html
IHO S-52	Specifications for chart content and display aspects of ECDIS (e.g. Ed. 6.1.1)	IHO publication; see https://iho.int
IEC 62288	Presentation of navigation-related information on shipborne navigational displays	IEC 62288:2021 (and amendments); https://webstore.iec.ch
reTerminal DM wiki	Hardware interfaces (backlight, buzzer, light sensor)	https://wiki.seeedstudio.com/reterminal-dm/

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This document is for guidance only. For formal compliance, refer to the official IMO, IHO, and IEC publications and your flag state / classification society.