I can't site my source as I read it a while ago but from what I read there is no evidence that this is true. According to the article a general rule of thumb is if your going to turn the light back on within 10 minutes it is better to leave it on. Also, florecent lights should not be used in areas where there will be continuos on/off switching. This is because florecent lights have x number of starts, after about 10,000 - 20,000 on off cycles the light is spent. Again I obtained this info. from an online article so take it for what its worth.