Our circadian rhythms are easily disrupted by working unsocial hours and poor lighting - even the brightest office will only provide about 500lux. A misaligned body clock is the reason we have times at work when we feel lethargic and find it hard to concentrate and get going. Instead of grabbing a coffee, try bright light first thing for a quick, natural energy boost. Use a light at work to avoid that mid-afternoon dip or, if you work nights, during your shift to help perk you up and improve alertness. Whatever hours you work, extra light when you're awake will help to convince your body clock it's daytime so you sleep better when you get home.