Ask Otto

Byter Steve writes:

Diane assured me that it is cheaper to leave a fluorescent light on than to turn it on and off every time you want to use it. I have heard this before, but I believe it to be “an old wives tale”. Can you tell us who is right please?

Steve, have you not heard of non gender specific language, aka gender neutral language? Linking elderly married women with untrue stories, ie “old wives tale”, is asking for trouble, my non PC friend.

Let me summarise for you what various authoritative websites and sources agree upon:

• Prior to the 1970’s, manufacturers did recommend that lights be left on to save the life of the tube. Switching on and off reduced the life of the tubes by as much as 20 per cent, with the consequence that city office buildings were lit up at night like Star City. The thinking was that it was cheaper to spend a bit extra on electricity than to have to send maintenance guys to change the tubes every few months.

• The 1970’s saw the introduction of longer lasting tubes with quicker start up operation, with the consequence that it is better to switch off the fluorescent light when leaving a room. The energy saved by switching off is greater than the energy used to start up.

• According to the Australian national University, the process of ignition takes 300 times the operational current, for a period of 0.3ms (0.0003 seconds). That means that switching your light ON takes as much power as the tube consumes in 0.09 of a second of operation. So if you leave the room for longer than 0.09 seconds, turning your light OFF will save energy.

• Switching off and on continually will, however, reduce the life of the light bulb/tube, a relevant factor in that the newer fluorescents are more expensive than the older incandescents.

• The advice popularly given is to switch off if leaving the room for more than 5 minutes. This strikes a balance between energy use and light life.

• The Australian National University uses a 45 minute rule; switch off if leaving for more than 45 minutes. This will increase the operational life, that is, the number of operational days before replacement is required.

In the long run, it makes little difference to the overall saving of energy whether you switch off or leave the light on, given that you share the line with hundreds of thousands of others, although it will make a difference in your electricity bill and light bulb bill.

Where a real difference can be made is by having regard to the following.

• Switch to fluorescent bulbs. Compact fluorescent light bulbs use 75% less energy than an equivalent incandescent bulb, with lighting accounting for 5% of household greenhouse gas emissions.

• Switch off appliances that are on standby and turn off anything that doesn’t need to be on. Appliances on standby consume up to 10% of your electricity bill. Turn them off at the wall when not in use.

• Insulate ceilings, walls and floors. An uninsulated home can lose up to 35% of heat from the ceiling, up to 25% through walls and up to 20% through floors

• Cut hot water usage by installing a 3 star rated showerhead, and by taking shorter showers. An average house using electricity for water heating generates about 4 tonnes of greenhouse gas each year.

• Use cold water to wash clothes and the sun to dry them. The energy used to heat the hot water for a washing machine generates greenhouse gases. By using cold water instead of hot water it will save up to 3.5 kilograms of greenhouse gases per wash. A clothes dryer can generate more than 3 kilograms of greenhouse gases per load.

• Buy energy-efficient appliances with low standby power usage. These products use minimal power when in standby mode. Correspondingly, existing older items such as the beer fridge in the garage, could be electricity guzzlers.