CAVE LIGHTING

Lloyd Robinson

INTRODUCTION

Fixed show cave lighting installations are often the "Orphan Annie" of a cave development programme, with little planning given to the layout. One does not have to look far in Australia to see examples of this; exposed and unsightly cable runs; voltage fluctuations resulting in lights dimming or brightening as the load on the system varies; lights balanced on rocks etc showing signs of having been re-positioned many times; oversize switchboards placed in prominent positions rivalling the show scenes. Frequently the job of deciding the position of electrical equipment falls to the electrical people who may not necessarily be experienced in feature lighting. Not many show caves can support an electrician on the staff with a consequence the nearest local electrician is engaged to carry out installation and maintenance work. Usually such electricians are experienced in household installations and are likely to treat the cave installation in much the same way as another house job; to be completed in the quickest way possible.

A show cave lighting installation need not be the problem that it is often taken to be provided that it is planned prior to work commencing, particularly in regard to switchboards and the main distribution cables supplying the switchboards. With a well planned distribution system the final circuits can be altered or added to without much trouble whereas the distribution cables and switchboards, once positioned, are not so easily moved.

The main objects of a fixed cave lighting installation are:

1. Enable safe movement of tourists through the inspection tour.
2. Show features to their best advantage.
3. Have minimal effects on the cave.
4. Operate safely and reliably.
5. Cost factors.

Of the various means of lighting available electric lighting is likely to remain the main form of show cave lighting in the foreseeable future. Over the past thirty (30) years there have been great advances in cable construction and globe design. Over the same period even greater advances have been made with control devices. With solid state switching and controls it is possible to install equipment without the need for manual operation. Applied to cave lighting, controls can be arranged to be switched on by the presence of a person. Taken one step further with dimming controls on self-guided tours the lighting can be controlled to gradually come on as the party advances, reaching full brilliance as the party arrives and dimming and finally going out as the party moves on. Such a system would be suitable on a self-guided tour with technicians on hand but would not be a proposition for most caves.

Before embarking on a cave lighting installation some thought must be given to the standard of the installation and the requirements of the electrical Supply Authorities inspectors. The code covering electrical installations in Australia is the Standards Association of Australia Standard CC1, Part 1 - 1969 S.A.A. Wiring Rules plus amendments. These rules relate to electrical installations in or on buildings, structures and premises and make no specific mention of cave installations. A variety of requirements have been placed by the different Supply Authorities throughout Australia in applying the S.A.A. Wiring Rules to show caves, in some cases to the detriment of the cave.

I believe that a safe and workable cave installation can be installed without deleterious effect on the cave and that such an installation would come within the meaning of the definition on Page 16 of the above Standard headed: "0.4 UNUSUAL INSTALLATIONS ........"

"Certain installations or portions of installations which are unusual because of their method of use or of particular circumstances are not covered in detail by these Rules. Details of such installations which do not provide literal compliance with the Rules should be submitted to the Inspecting Authority who, having regard to all the circumstances, may approve the installation as complying with the spirit and intention of the Rules if, in its opinion, the arrangement and method of use will result in a degree of safety from fire and shock not less than that which in other circumstances would be provided by compliance with the Rules.

Such installations may be referred to the Wiring Rules Committee of the Standards Association of Australia for advice where necessary.

NOTE: Unusual installations may include research, testing, educational laboratories and the like, which are staffed only by skilled persons or where a satisfactory degree of safety is provided by the establishment of safe working methods, and other installations where equivalent safeguards are provided by controlled methods of operation."

ELECTRICAL SUPPLY

The most desirable is the local supply. This involves overhead transmission lines, a transformer etc, as most caves are not near town electrical reticulation. Overhead transmission lines require a large clearing either side of the line. If the cave is in timbered country the overhead line should end some distance from the cave entrance, with the step-down transformer pole mounted and an underground supply laid to the cave entrance. Where there is no local supply an on-site A.C. generating plant is the alternative. Direct current (D.C.) is rarely used, one major disadvantage being that the generated voltage cannot be easily altered. Care needs to be exercised with plant location so as to avoid exhaust emissions and engine noise entering the cave. While it is desirable to keep the generating plant fairly close to the cave to avoid voltage losses it should not however be installed on top of a near surface cavern.

The capacity of the supply needs to be adequate to cater for the greatest load plus a fifty (50) percent reserve with protection devices set so as not to cause spurious power interruptions. In the choice of operating voltage there is a strong case for the use of the Australian standard 240 volt, 50 hertz, single phase supply if for no other reason than to allow the choice of a wider range and ready supply of lamps. Voltage regulation is more likely to be maintained with a 240 volt system than with a lower voltage. If the day ever comes when some of our longer caves are developed for tourism there will be the need to run higher than standard voltage into the cave transforming it to operating voltage within the cave. This practice has been in use in underground mines for many years.

MAIN SUPPLY CABLES

The key to a satisfactory cave lighting installation are the main supply cables running into the cave to the switchboards. These cables need to be the double insulated type and of sufficient size to maintain adequate voltage regulation at the farthest reaches of the system. In calculating the size of cables required the lengths of cable runs involved and the maximum load on the system plus any future additional load or extensions to the tour must be known. Undersize mains cables are the reason why the lighting fluctuates in some of our show caves. This paper assumes that caves to be developed have been thoroughly explored and any passages or other entrances to the cave that can be used to shorten the main supply cable runs are taken advantage of.

Thermoplastic-sheathed (TPS) cables are the most suitable for cave use (thermoplastic covers polyvinyl chloride (PVC) and other similar materials).

Where cost of suitable sized copper mains is a problem there is no reason why PVC covered stranded aluminium cables cannot be used. Aluminium has a conductance of eighty (80) percent to that of copper; the comparable size increase is not great. Further there is a weight advantage which makes for easier positioning of cables in awkward places. Care needs to be exercised in terminating aluminium cables; there are special terminators for the purpose and the suppliers instructions should be adhered to. For ease of installation in confined situations it is advantageous to run single core double insulated cables rather than one multi-core cable.

Since a fault on the mains cable can put the whole system out of action the placement and fixing of such cables deserves special attention. Where possible cables should be kept clear of pathways. Where this is not possible extra covering of the cables is required; in no case should it be possible to contact an unprotected cable from a pathway. In places of close confines with no alternative passages special provision is needed to carry the mains and path lighting cables.

Metal type cable fixings are not successful in fixing cables in caves. A more permanent fixing is the use of nylon straps anchored with grouted nylon bolts and nylon nuts either side of the cables. Another, but slower method, is the placing of a small concrete bridge across the cable(s) at fixing points. As with all cables, mains cables should be secured except in small passages too small for human entry.

Mains cable can be supplied in lengths long enough to suit any run likely to be encountered in show caves without the need for joining the cable. In the event of a join being required to any cable other than at a switchboard Scotch Cast joining kits as supplied by the SM Company are suitable.

SWITCHBOARDS

As cave environments are often harsh on metal the use of all insulated poly-carbonate type switchboards eliminates the problems of moisture damage. Sealed versions are available with cable entry seals and transparent covers allowing ready inspection and the sealing of electrical components from the cave atmosphere. In cases of high humidity an active desiccating agent such as 'silica-gel' can be placed inside the enclosure before final sealing.

Essentially each switchboard should have:

1. Main isolating switch controlling the board.
2. Provision for control and protection of each circuit.
3. Spares of item (b) for possible additions or further split-up of existing circuits.
4. Indicators to indicate which circuit(s) are on.
5. Name of circuit near each appropriate switch (e.g. (1) Shawl (2) In-bye track lights 1 etc)
6. A general purpose outlet (power point) for the use of power tools, film/TV unit lighting etc
7. Similar panel layout to other switchboards in the show cave system.

Two (2) main forms of control and protection of final circuits are available:

1. Switches and fuses
2. Combination switch and protection device known as an "air circuit breaker" (ACB).

There are advantages and disadvantages of both systems, the latter having more to offer for use in caves. If there is an electrical fault on a lighting circuit there is nothing that can be done during the tour. In some cases when a globe fails the filament momentarily shorts the power prongs within the globe causing the protection device to interrupt the circuit. With such a failure the ACB can be reset and switched on to operate the remaining light(s) on the circuit. If ACBs are installed they require back-up protection such as a HRC fuse; either one fuse protecting each switchboard or the surface switchboard for the whole system. Information can be obtained from the ACB suppliers as to the size of back-up protection required for a particular installation.

Where it is desired that a circuit needs to be operated from more than one position a relay can be installed in the switchboard to switch the circuit. Relay control wiring can be run to as many miniature ON-OFF push button control stations as desired.

Switchboards are usually installed in areas where the guide gathers the whole party together and operates the switches to produce the various lighting effects. A position for the switchboard needs to be chosen so that the guide has easy access to it and can view the tour party as well as the lighting display. The small physical size of the switchboard described above offers more scope for positioning as it will not be such a dominating feature. Self-guided tours should have no control equipment mounted within reach of tourist paths.

PATH OR TRACK LIGHTING

The general idea of a conducted cave tour is of a party advancing into the cave in stages from one viewing stop to the next with separate lights lighting up the pathway between stops; such lighting being controlled by two-way switching.

The above is not always the case as a number of Australian show caves have the major part of their inspection tour over small passages and caverns where the feature lighting also serves as path lighting. Our show caves with a sizeable cavern usually have the cavern itself as the extent of the tour with the feature lights on during the tour and tourists viewing the cavern's features from various vantage points. Under these conditions there is not much scope for pathway lighting to be essentially as such.

The main objectives of cave pathway lighting are:

1. Even illumination of pathway.
2. Illumination of obstructions (low ceiling).
3. Minimum spillage of light off the pathway.
4. Concealment of lights, fittings and wiring so that they are not visible from the pathway.

To achieve the objectives, low level lights should be mounted close to the path on either or both sides and from 200mm to 600mm above the level of the path. Positioning of these lights can be more trouble than with feature lighting; in many places special light concealing boxes will have to be built to conceal lights where there are no natural places available. Sometimes the cementing of a selected rock or two to a natural feature will conceal a light.

Light concealing "boxes" are best built of rocks that will blend in with the cave and do not need to be very big to house an ordinary lamp and fitting. Cement is used to cement the rocks together. Rather than leave a light box stand on its own it can be cemented to a rock floor, a boulder or in the case of a soil floor, to a couple of spikes driven into the soil. Visible cemented joints need a "dusting" of surface rock scrapings while the cement is still wet to blend it with the surrounds. Advantage can be taken of a turn in the pathway by mounting a light on the outside of the turn and directing the light along both arms of the path; two lamps being mounted in the one concealment as the failure of a solitary lamp in this case would black-out too much of the pathway. Obstructions such as low ceilings need to be well illuminated.

As with other electrical fittings mentioned the all-insulated fittings for pathway lights obviate the necessity of earthing. There is no ideal light fitting available in Australia for cave track lights. Possibly the best to use is the bayonet bakelite holder anchored to a PVC junction box with the metal parts of lamp and holder coated with black silicone grease. For lighting over a limited distance ordinary 25 to 60 watt lamps will suffice and small inbuilt reflector type lamps for greater distances. However, rather than try to use a reflector type lamp to illuminate a long length of pathway it is better to install more lights. In some places fluorescent lighting could be used to advantage as it throws a soft even light making it suitable for lighting a path, but it has a number of drawbacks for cave use. Its initial cost is much higher than ordinary lights; its size makes it more difficult to conceal and from a maintenance viewpoint there is more electrical parts to give trouble especially in a humid or wet cave. There are all insulated versions available which do not require earthing such as the Thorn "Casalux" 20 watt fluorescent light which has a polycarbonate visor type diffuser and a glass filled nylon base. If installing in a cave care should be taken to seal the unit interior from the cave atmosphere paying attention to the cable entry and mounting holes. Whatever type of path lighting used the lights should be directed onto the path. With no stray light the more adventuresome tourists are not so likely to wander off the pathway.

Grey coloured flat twin-core 3/.036" PVC double insulated cable is as good a cable as any for wiring up cave lights. The author has examined cable of this construction with more than 20 years underground use without any signs of ill effect. Other colours are available if required. Pyrotenax cable has been suggested as suitable for cave wiring. If the high cost of the cable is not the problem the cable should be purchased with a PVC serving to eliminate any risk of the bare copper discolouring the surrounding walls/formation where the cable is laid.

Some authorities require that path lighting be left on to the surface so that anyone becoming indisposed during the tour can make their way out of the cave. Where path lighting is the only form of lighting available over a section it is good practice to have such lighting on two circuits, in case of a fault at least some lighting remains. In connecting up, every alternate light would be on a different circuit.

FEATURE LIGHTING

The most important aspect as far as the paying tourist is concerned is feature lighting. It is not the intention of this paper to lay down hard and fast rules for feature lighting. It can truly be said of caves that no two scenes are similar and that each has its own special problems when it comes to displaying them. Further it is unlikely that any two people would light up a cave scene the same way. In general terms the larger the cavern the features are in, the easier it is to provide fixed lighting. Frequently in the confines of a cave the bringing together of the features, the tourists and the lighting takes last place. During initial planning where there is a choice of positioning viewing areas and access paths consideration needs to be given to lighting problems. Quite often a suitable light concealing ledge or alcove can be hidden from view by altering the position of a viewing area in the planning stages.

In the interests of conservation lights grouped in clusters are better than lights scattered around the cavern; this alleviates the problem of maintenance wear on the cave. It does not take long for areas leading to and around lights to get that used look; for this reason never mount lights where it is necessary to clamber across formation to change globes.

Most show caves are like a photographic darkroom, any lighting is completely under the control of the planners/installers. If predictions are correct, in the future we will have a boon to cave lighting in the form of self powered continuous energy lights needing no wiring although control of such lighting is not forecast. For the present we have a wide range of lighting available from ordinary incandescent lamps, inbuilt reflector lamps, fluorescent lamps through to discharge type lamps. One of the most useful for cave lighting is the all-weather sealed beam incandescent lamp with inbuilt reflector and lens. The use of such lamps makes for a more compact unit compared with non reflector type lamps mounted in dish reflectors; the inbuilt reflector, being totally sealed, does not suffer from the cave atmosphere. Crompton, Parkinson and Phillips supply a compact all-weather 100 watt and 150 watt PAR38 flood and PAR38 spot lamps with built in parabolic reflectors which have been proven in cave use over a number of years. To mount these lamps Phillips supply an all-insulated, fully adjustable "Paraflood" lampholder which has a silicone rubber seal-ring that fits between lamp and holder effectively sealing the metal contacts. The assembled unit is light enough in weight to be anchored by grouted nylon bolts. The lampholder when adjusted can be locked in position. Using the lighting just described allows the lights to be mounted away from the features to be displayed. This in turn opens up more mounting positions and hopefully it should rarely be necessary to have the mount lights on formations. Due to the atmospheric conditions of some caves a hot spot is created in front of reflector type lamps by the concentrated light reflected off the moisture laden atmosphere. In such caves it is advisable to not only conceal the light but the immediate area in front of the light as well. As with pathway/track lighting, light concealing "boxes" may have to be built, using the same methods of construction as previously described, to conceal lights when viewed from tourist access areas.

Finding positions for show lights so that they are hidden from view and effective in displaying the features can have its problems. With harsh lighting or lights mounted directly in line with the viewers and the subject can have a flattening effect and tends to make three dimensional objects appear two dimensional. The use of temporary portable lead lights is a help in determining where to position lights. Lights need to create highlights and shadow and make the subject stand out from its surroundings. This need not necessarily be achieved by direct lighting only as reflected light from indirect lighting or a combination of both direct and indirect lighting can create pleasing effects. Where there are limited places for light concealment and where conditions permit, the path can be raised and built in "T" form with the lights fixed on the underside of the raised pathway.

In many show caves with features in confined passages where the tour party have to move along in single file, the feature lighting doubles as path lighting being mounted in a position where it does not do justice to either. When installing lights in such confines it is best to install the required feature lights as feature lights first and view its spillover effect as path lighting. Further path lights can then be added where necessary to illuminate the pathway. For lighting up small features there are available small reflector type incandescent lamps, or if space and conditions permit fluorescent lighting can be considered. Ordinary lamps mounted without reflectors close to formations etc. are more likely to give rise to undesirable growths.

There are arguments for and against the use of coloured lighting in caves. If the formations are naturally richly coloured there is hardly any need to add coloured lighting. Should coloured lighting be installed the switching needs to be arranged so that the coloured lights are independently controlled so that the scene can be viewed under natural lighting as well. There is one form of coloured lighting which creates interest and that is the use of a colour wheel where a powerful light is mounted behind a six to eight segment rotating colour wheel with various colours. The wheel is rotated by a low voltage motor at approximately one revolution per minute. A theatre spotlight makes a good lamp housing and the light is directed as desired.

Other types of lighting can be used for special purposes such as quartz halogen lamps mounted in reflectors to highlight a special feature high up on a wall or ceiling. There is a problem of short life with this type of lamp if it is too frequently switched. For lighting up large caverns with few features (i.e. a Nullarbor cave cavern) one or two high wattage colour corrected gas discharge lamps strategically placed would suffice. Like quartz lamps these lamps do not give a long life if frequently switched.

Some balance needs to be maintained between the intensity of feature lighting and path lighting so that the tour party does not have to contend with re-adjustment of eyesight from one lighting condition to another; a process which slows progress.

Similar cables can be used for feature lights as used and described for path lighting. Cable sizes need to be determined to avoid the limits of voltage drop at the farthest parts of the system. Also as described earlier cables should be hidden from view and pins to fix cables should not be fixed into formations. Use of reflector type lamps with their longer light throw will assist in keeping cable runs shorter.

GENERAL

By eliminating certain lights (fluorescent, gas discharge) pyrotenax cable and GPOs an all insulated system is gained which does not require any earthing. Most would consider GPOs essential for the uses described earlier. In most caves suitable earth points would be found within the cave; tests would need to be carried out to determine this. The use of pyrotenax cable would probably be frowned on by the Inspecting Authority as it is not allowed to be used around swimming pools. (GPO - general purpose outlets?? - CD ed)

In the interests of safety for the electrical maintenance staff it is good practice to have the main isolating switch on each cave switchboard separated from the rest of the board by insulating material. In most cases the electrician works alone and to save having to return to the surface to restore power after repairs leaves the power on while carrying out repairs. With the main isolator fitted with a barrier the faulty section can be effectively isolated from within the cave. In the case of two-way path switching special attention needs to be given to tagging such switches to indicate where they are supplied from.

REFERENCES

1. Phillips Lamp and Lighting

2. Westinghouse Lighting Handbook

3. SAA Wiring Rules CC1 Part I - 1969 plus amendments (10)