Lights On or Off – What Should We Really Do?

‘It uses more energy to keep turning the lights off and on, so just leave them on’. We probably all grew up with this one, but is it really true? Well, naturally the issue is a lot more complex than you might think – but leaving all of the world’s lights turned on based on this logic would clearly be idiotic, so I’ve dug around and found a collection of research-based conclusions that bust this myth.

lights off

To put things in context;

  • The studies compare incandescent globes with Compact Fluorescent Light-globes [CFLs];
  • A globe’s [or ‘lamp’] lifespan [rated hours] depends on both how durable the design is, how often it’s turned on and off [uses], and the operating cycle [how long it’s left on for]
  • CFLs are rated at around 8,000-10,000 hours life span [let’s say, to keep things easy], based on a typical operation of 3 hours on then 20 minutes off;

One of the best facts I found was from the US Dept. of Energy site: when we switch on a CFL it has an ‘inrush’ phase where it does use more energy, but only for 1/120th of a second, equivalent to 5 seconds of operation. So unless you’re a little kid standing there flicking the lights on and off fifty times a second and going ‘whooohooooo’ then don’t stress – just turn them off.

For some further detail, this Rocky Mountain Institute study conducted in 2008 has some great findings and write-up (i.e. easy for me to understand). It found that no matter what, a CFL still trumps an incandescent globe. Increasing the uses and/or decreasing the operation time, e.g. switching it off and on many times a day and only running the light for 5 minutes at a time will significantly reduce the lamp’s lifespan, however even then a CFL will still;

  1. pay itself off with the energy savings;
  2. last longer than an incandescent globe;
  3. emit less greenhouse gases [by a long way];
  4. emit less mercury [by a long way].

In the office the story is pretty much the same. Lights such as T5s are rated for 10,000 or more hours and will typically stay on all day. Switching them off at the end of the day is part of what the lamps are designed for – at least 6,000 cycles and rising as the lamp technology improves – so don’t fret, just turn them off when you’re done, even in the smaller rooms that you might visit a few times a day.

Hopefully this leaves you feeling illuminated for the week : )


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