...that have always intrigued you about the world will appear in this,
your section, and be answered by other readers. Please address
your answers and questions to ‘Curiosities’.

Is it better to leave a fluorescent light switched on when you leave a room?
If so, at what point does it become more economic to switch off?

. In the mid-1970s I asked the same question of the then Scottish Electricity Board. They sent out a man to explain to me the mysteries of 'starting' and 'running'. His opinion was that, in my situation as a teacher, it would be better to leave the lights on for the 15 minutes of the mid-morning break but to switch them off during the 50-minute dinner break and, of course, at the end of the school day.

MM Hendry,
Edinburgh, Scotland.

. Fluorescent lights consume less energy than incandescent bulbs to give the same amount of light. But fluorescent light bulbs contain a device called a 'ballast' to start the lamp and regulate the electric current. The ballast consumes extra power when the lamp is switched on so the running costs of a fluorescent light will not be lower if the lamp is regularly switched on and off. However, of greater economic concern is the effect on life expectancy of the bulb. The UK Consumers Association has run tests on fluorescent lights and notes that regularly switching a lamp on for only five minutes could result in it lasting just 20 per cent of its rated life. And fluorescent lights are expensive to replace. If left on continuously, however, a lamp may last 150 per cent longer than its average life expectancy. So when does it become economic to switch it off?

US lighting consultants Rising Sun Enterprises of Colorado recommend the following: switch off a fluorescent lamp if you're going to be out of the room for more than 15 minutes. For an incandescent bulb they recommend just five minutes. But for the new compact fluorescent bulbs they suggest switching off only if you are going out for more than half an hour - an indication of the superior energy savings of such bulbs.

However, the best rule of thumb must surely be: 'If in doubt, switch off'. In so doing you reduce your electricity bill and cut your contribution to global pollution created by power stations.

Philip Parker,
Stroud, UK

. The short answer is 'no'. When you switch on there is a short surge about two or three times greater than the running current. But this only lasts about two seconds - insignificant compared with the power consumed while running. Bulbs used to suffer from a shortening of their lifetime every time they were switched on but this is no longer a problem with the modern types.

Tim Williams,
Chichester, UK

I understand that a waterless WC - using sawdust to produce a high-grade compost
- has been invented by a Swede. Can anyone tell me more

. It can be sited under a house and is ventilated through a flue to above roof level, with a small fan to assist air circulation. The toilet can be cleaned out once compost - which may include kitchen waste - has been produced. And it is reported not to smell. I understand one company in the UK deals in these: Compost Toilets, Swedal Leisure (UK) Ltd, P0 Box 14, Egham, Surrey TW2O OQP.

A Chapman,
Brighton, UK

How often I have heard the expression 'charity begins at home' used to justify a lack of charity.
Who originally said it, to whom and why?

Dave Phillips,
Gwent, Cymru

Is it true that the menstrual cycles of women living together in women-only communities (convents, for example) synchronize? And if so, why?

Zoe Simpson Green
Oxford, UK

How much money is there in the whole wide world?

Robert French (aged 10)
Bristol, UK

Is it true that Great Britain is still paying for the First World War and if so to whom?

Elizabeth Atkinson,
Hastings, Aotearoa/New Zealand

If you have any questions or answers please send them to Curiosities,
New Internationalist, 55 Rectory Road, Oxford OX4 1BW, UK,
or to your local NI office (click here for addresses).