DST is not universally accepted; many localities do not observe it. Opponents claim that there is not enough benefit to justify needing to adjust clocks twice every year. The disruption in sleep patterns associated with setting clocks either forward or backward correlates with a spike in the number of severe auto accidents. Also, there is also a question whether the savings in lighting costs justifies the increase in summertime air conditioning costs. While most people use more sunlight under DST, most people also experience more heat, which prompts many people to turn on the air conditioner during the warmer afternoon hours. When air conditioning was not widely available, the change did save energy; however, air conditioning is much more widespread now than it was several decades ago.