To ensure a safe working environment, together with off duty comfort in the accommodation quarters on board your ship, a considerable proportion of the generated electric power is absorbed in the ancillary services. Lighting of the ship's deck areas, engine room and accommodation to meet specified levels of illumination is provided by various light fittings (luminaires) designed to work safely in their particular locations. The hotel services for food storage, preparation and cooking, together with accommodation air-conditioning and laundry services, are essential for the general maintenance of the mariner.
Historically, the original application of electricity in ships was for lighting. Oil lanterns were a definite fire risk and the ship's lamp trimmer had great difficulty in maintaining his navigation lights in stormy weather. To meet the safety and comfort levels of illumination required throughout your ship a wide range of lighting fittings (luminaires) are used. The power ratings of the lamps used will vary from a few watts for alarm indicator lamps to a few kW for deck floodlights and searchlights (e.g. a Suez Canal Projector Light).
Group replacement of lamps is often considered by shipping companies to be more economic and convenient than individual replacement following lamp failure. Cleaning of the fittings can also be carried out during group lamp replacement so maintaining a high luminous efficiency. Lamp end caps are many and various but the most common types are screw and bayonet fittings. Broadly, the luminaires employ one of two general lamp types classified as: 1. Incandescent 2. Discharge
Incandescent Lamps The most common lamp used for general lighting is the simple filament type. A current is passed through the thin tungsten wire filament which raises its temperature to around 3000 °C when it becomes incandescent (it glows). The glass bulb is filled with an inert gas such as nitrogen or argon which helps to reduce filament evaporation to allow an operating life expectancy of about 1000 hours. Lamp power ratings are available from 15 W to 1000 W.
Discharge Lamps The light output from a discharge lamp is generated by the flow of current in an electric arc between two electrodes through a gas and metal vapour inside a sealed glass bulb or tube. The most common metal vapours employed in discharge lamps are: 1. Mercury (as used in a fluorescent tube) and 2. Sodium
Voltage Effects on Lighting Naturally, all lamps are designed to produce their rated luminous output at their rated voltage. An overvoltage on an incandescent lamp produces a brighter and whiter light because the filament temperature is increased. Its operating life is, however, drastically reduced. A 5% increase over its rated voltage will reduce the lamp life by 50%. Conversely, a supply voltage reduction will increase the operating life of a GLS lamp but it produces a duller, reddish light. Lamps rated at 240 V are often used in a ship's lighting system operating at 220 V. This under-running should more than double the lamp life.
Similar effects on light output and operating life apply to discharge lamps but if the supply voltage is drastically reduced (below 50%) the arc discharge ceases and will not re-strike until the voltage is raised to nearly its normal value. A fluorescent tube will begin to flicker noticeably as the voltage is reduced below its rated value.
Navigation and Signal Lights The number, position and visible range of navigation lights aboard ships are prescribed by the International Maritime Organization (IMO) in their "International Regulations for Preventing Collisions at Sea". By far the most common arrangement is to have five specially designed navigation running lights referred to as Foremast, Mainmast (or Aftmast), Port, Starboard and Stern.
Two anchor lights, fitted forward and aft, may also be switched from the Navigation Light Panel on the bridge. The side lights are red for Port and green for Starboard while the other lights are white. For vessels length more than 50 metres, the masthead light(s) must be visible from a range of six nautical miles and the other navigation lights from three nautical miles. To achieve such visibility, special incandescent filament lamps are used each with a typical power rating of 65 W but 60 W and 40 W ratings are also permitted in some cases.
Due to the essential safety requirement ( for navigation lights it is common practice to have two fittings at each position, or two lamps and lampholders within a special dual fitting. Each light is separately supplied, switched, fused and monitored from a Navigation Light Panel in the wheelhouse. The electric power is provided usually at 220 V a.c. with a main supply fed from the essential services section of the main switchboard.
An alternative or standby power supply is fed from the emergency switchboard. A changeover switch on the Navigation Light Panel selects the main or standby power supply. The Navigation Light Panel has indicator lamps and an audible alarm to warn of any lamp or lamp-circuit failure. Each lamp circuit has an alarm relay which monitors the lamp current. The relay may be electromagnetic or electronic.
Various signal lights with red, green, white and blue colours are arranged on the signal mast. These lights are switched to give particular combinations to signal states relating to various international and national regulations. Pilotage requirements, health, dangerous cargo conditions, etc., are signalled with these lights. White Morse-Code flashing lights may also be fitted on the signal mast. The NUC (Not Under Command) state is signalled using two all-round red lights vertically mounted at least 2 m apart. Such important lights are fed from the 24 V d.c. emergency supply but some ships may also have an additional NUC light-pair fed from the 220 V a.c. emergency power supply.
Emergency Lighting Depending on the ship's classification, e.g. ferry, ro- ro, gas carrier, etc., and tonnage the Safety of Life at Sea (SOLAS) Convention prescribes minimum requirements for emergency lighting throughout the vessel. Emergency light fittings are specially identified, often with a red disc, to indicate their function. Most of the emergency lighting is continually powered from the ship's emergency switchboard at 220 V a.c. A few emergency lights may be supplied from the ship's 24 V d.c. battery, e.g. at the radio-telephone position in the wheelhouse, the main machinery spaces and the steering flat.
Some shipping companies now fit special battery-supported lighting fittings along main escape routes in the engine room, accommodation and at the lifeboat positions on deck. Generally, such emergency lights in the accommodation are arranged to produce light immediately on mains failure. Boat station emergency lights are switched on when required. Inside the fitting a maintenance-free battery, usually nickel-cadmium, is continually trickle- charged from the normal mains supply via a transformer/rectifier circuit. The battery is then available to supply the lamp via a d.c. to a.c. inverter when the main power is absent. Usually the battery will only function for a few hours. This power supply arrangement is called an uniterruptible power supply or UPS. Such battery supported light fittings can be simply tested by switching off the normal mains power supply or, in some cases, by a test switch on the actual fitting. Periodic inspection and testing of all emergency lights is an essential requirement on all ships.
A visible, illuminated escape route reduces uncertainty and assists orderly evacuation. Passenger ships carrying more than 36 passengers are required by IMO resolution A752(18) to be fitted with Low Location Lighting (LLL) to identify escape routes where normal emergency lighting is less effective due to the presence of smoke. An LLL system must function for at least 60 minutes after activation and it should indicate a line along the corridors of an escape route. The installation of LLL should be on at least one side of the corridor, either on the bulkhead within 300 mm of the deck or on the deck within 150 mm of the bulkhead. In corridors more than 2m wide, it should be installed on both sides. The LLL light sources may be low power LED's, incandescent lamps or a photoluminescent material containing a chemical that stores energy when illuminated by visible light. Of these sources, the LED and incandescent lamp are the most effective. For hazardous areas such as car decks on a ferry, an intrinsically safe (Exia) version can be installed.
Maintenance of Lighting Fittings The performance of electric lamps will deteriorate with time. Eventually they fail and the lamps must be replaced. Simple lamp replacement becomes the most obvious maintenance task. When a luminaire fails to light-up when switched on, it is natural to suspect lamp failure. If this does not solve the problem, checks on the lamp control equipment and power supply must follow. An incandescent lamp may be checked (out of circuit) for low- ohm continuity using a multimeter. If the lamp appears intact then the fault must lie in the supply or its connections. Voltage and continuity checks of the supply, fuse/ MCB and ballast circuit must be applied. Remember that a single earth fault on an insulated two-wire lighting supply will not blow a fuse. However, a similar earth fault on an earthed supply system (as used for a 110V transformer supply to deck sockets for portable tools and handlamps) will blow a fuse.
A maintenance check list: Remember that it is good practice to replace both fuses after clearing a fault which has ruptured only one of them. When replacing a lamp, ensure that the circuit is dead and isolated while removing the old lamp and inserting the new one. The glass bulb or tube of an old and corroded fitting may break loose from its end-cap while attempting to remove the lamp. If the supply is still connected, it is relatively easy to cause an accidental short- circuit during the removal process and the corresponding arc flash may cause blindness, burns and fire.
Always replace a lamp with the correct size, voltage and power rating for the fitting it is housed in. Overheating and fire can easily result by using a higher powered incandescent lamp than the fitting was designed for. Check the lampholder wire connections behind the lampholder for signs of overheating (hard, brittle insulation on the wires) and replace if necessary. Take care when disposing of lamps, particularly discharge tubes, which should be broken (outdoors) into a container (e.g. a strong plastic bag) to avoid handling the debris.
Remember that in a fluorescent lamp circuit the capacitor may remain charged for a while after switch off unless fitted with a discharge resistor. Play safe, discharge the capacitor with a screwdriver blade before touching its terminals. Cleaning of the lamp glass and reflectors is essential for safety and necessary to maintain the luminous efficiency of the luminaire. Particular care should be paid to the maintenance of the watertight integrity of exposed luminaires (e.g. for navigation, signal and deck lighting) at their flanged joints and cable gland entry. Similarly, a regular inspection of all portable handlamps and portable cargo light fittings, together with their flexible cables and supply plugs, should be undertaken.