Whenever possible I like to reduce the amount of artificial light I use while working. When in an office with great natural light, I opt to turn off the overhead lights and enjoy working in nature's glow. If that's not quite enough, I've added a small LED light to add that extra bit of brightness.

If you're in a windowless office, try opting for a lower energy desk light that provides you with the illumination needed to work, but not much extra. It will help increase your focus, calm the senses and reduce energy consumption.