Lighting for Motorhomes - Caravan and Motorhome Books

LIGHTING FOR MOTORHOMES

Until recent times, the only practicable way of obtaining light has been to cause something suitable to become very hot. Once beyond a certain temperature, part of the heat energy produces visible light. But whilst candles and campfires are romantic, they are not necessarily convenient, and certainly not efficient. Even when evolved as electrically heated filaments inside glass envelopes (incandescent globes) only 10% of the energy is turned into visible light. Halogen globes are twice as efficient but this still means they waste 80% of the energy. Despite their present popularity, their place in history will be to mark the end of creating light by heating things up.

Fluorescent lights work on a different principle. Instead of causing something to come to white heat, a fluorescent tube or globe uses electricity to generate intense ultraviolet light. This causes a phosphor coating to fluoresce and create light of the required colour: in this case white and minor variants of white. Fluorescents generate some heat through internal losses, but unlike incandescents, heating is not an inherent part of the light generating process.

Fluorescent lights are by far the most efficient lights of all. They use about one quarter of the energy of conventional incandescents, and about half that of halogen globes. Their drawback for motorhome lighting is that they require mains voltage, so some of their efficiency is lost in the inverter needed to drive them. Despite this, overall efficiency is still way ahead of anything else.

Traditional fluorescent caravan lights have inbuilt inverters that enable them to run from 12 volts. Other approaches are to run 240-volt versions from a common inverter, or to use the recently introduced very small inverters made to run standard 18-watt fluorescent tubes. They cost about $27.50 and, according to Val Rigoli of Fridge and Solar (Labrador, Qld), they readily flush fit into motorhome/bus ceilings.

Compact fluorescent globes are exceptionally useful in motorhomes, particularly as they are available in warm-white form. They are now available in five and eight watt sizes upward (the five/eight watt units are equivalent to 20- and 32-watt incandescents respectively). These globes are made as Edison screw and also bayonet fitting. They plug into existing (240-volt) light fittings. There are also 12-volt versions of this globe that have tiny inbuilt inverters.

Fluorescent lights are likely to stay ahead in efficiency for the next five years and possibly longer, but seem almost certain to eventually be taken over by LEDs (Light Emitting Diodes).

Like fluorescent lighting before it, LED technology is a different concept rather than a development of what came before. Coloured LEDs have been readily and cheaply available for many years, but it is only recently that white LEDs are beginning to be practicable for general lighting. Unfortunately a great deal of marketing hype gives the impression that their time is now, and that their place is here. But except for specialised applications this is far from reality

Much of the hype stresses that LEDs use only very small amounts of energy and this is undeniably correct. But what the promotion glosses over is that the reason they use only very small amounts of energy is because they equally produce very small amounts of light!

In reality, white LEDs only marginally challenge energy gobbling incandescents. At present bright white LEDs are in an early stage of development. There's little point in using them for general illumination because, on a dollar/per unit of light basis (dollars/lumen) their cost is hundreds of times greater than almost anything else. A 2-3 watt white LED costs about $50. A LED that provides the same general level of illumination as a 36-watt fluro would currently cost close to $500. (But see below regarding DIY).

But this does not mean LEDs are a waste of money or not worth considering for motorhome use. To the contrary - they work well in specific areas and applications. Some, for example, throw a narrow focused beam and this makes them very worthwhile as individual reading lights. Low wattage (2-3 watts) LEDs are now commercially available in the so-called M16 format (used for 10-50 watt dichroic (built-in reflector) halogen globes) and these will fit straight into halogen fittings. They also have the advantage of running almost cold.

White LEDs are also invaluable for night lights, where a very low light level is required for long periods of time. A single bright white LED will provide adequate such light, yet draws so little energy that a single 1.5 volt dry cell will suffice, or (but less efficiently) it can be run from the 12-volt dc supply. A very small halogen or fluorescent that produces the same amount of light would use even less energy - but as far as I'm aware, none exist.

Where more light is required, a number of LEDs must be used in unison. They can be connected in various combinations to obtain the light output required, and to suit 12 and 24 volts (dc) power. High light outputs can be obtained this way but so many LEDs are required that it is currently not practicable and certainly not economic. It's what marketing people call ‘early innovator territory'.

Also just appearing are longer, brighter versions of the LED strip lights that have been on the market for the past year or three. Earlier versions were useful for providing some light in dark cupboards etc, but are now becoming available for general lighting.

What all LEDs have going for them is ultra-reliability. Here, nothing else is remotely close. With no filament to break and no glass to shatter they are likely to last for at least ten years. This alone has already made white LEDs of vital interest to people, such as cavers, to whom reliability is paramount. It has also resulted in white, red and amber LEDs being used for truck rear and side lamp assemblies. (Coloured LEDs are generally more efficient).

A further and global benefit is that, whilst LED production is not totally environmental-friendly, it causes minimal harm compared with the mercury vapour used in most fluorescent tubes and globes.

This is a great area for people who feel like experimenting because multi-LED lights can be self-assembled at a fraction of the cost of their commercial equivalents.

Companies such as Altronics, Dick Smith, Jaycar and Oatly Electronics have a wide and affordable range of ultra-bright white LEDs, and also supply kits of the basic circuits needed to drive them from 12/24 volts. Such circuitry can be as simple as a single series resistor, but a little more sophistication will save a lot of energy.

Magazines such as Silicon Chip and ReNew frequently carry very informative DIY and other articles on LEDs (back issues are available from both).

Right now, white LED technology is in its infancy but major advances are all but certain to be delivered. The US Secretary of Energy goes so far as to state that LEDs are: ‘a revolutionary technological innovation that promises to change the way we light our homes and businesses.' This is particularly important in the USA. There, an indecent amount of energy is used to shift the heat generated by inefficient lighting.

Development is proceeding fast. Their efficiency is likely to surpass fluorescents within a few years and, as happened with pocket calculators, their price will eventually drop dramatically.

On a different note, many people email and/or telephone me for advice. The answers to almost all routine questions are in my books that are sold by the CMCA, but I'm always happy to answer questions from CMCA Members who have an unusual problem and/or have received conflicting advice. I do from time to time (like now!) have to remind people that as you get this free you cannot reasonably expect me to pay for the call. Some Members do.

My next Tech Notes topic will be a guide to batteries and their care and feeding. Batteries are not as odd as teenagers - but they sometimes get very close

Please note : Due to a printing error this table was omitted from December 2003 Tech Notes.

Table 1: Cable sizes for 12-volt fridge and other circuits. The sizes, in square millimetres, (and, in brackets, AWG) cause less than 3% voltage drop at the maximum distance in each range. In the above Table, 4 mm auto cable can replace 1.5 sq mm, and 6.0 mm auto cable can replace any size up to 4.0 sq mm.