Good lighting is essential

In your office as in any space where you live, good lighting is essential.
Ideally you want as much natural daylight as possible. If your space has a window, it will enhance the lighting.
Daylight is the most evenly balanced source of white light available, in that sunlight has an approximately equal proportion of each color of the spectrum. The color of natural light also differs based on geographic location. It is always beneficial to have as much natural light as possible in the working area.

If in your office no daylight is available, a combination of general and task lighting will be required. A high-quality task light will be essential for late nights or cloudy days. If your office is in a room without windows, check out daylight-replicating light sources that will provide energy-efficient, full-spectrum lighting.
Many ergonomic task-lighting fixtures have dimmer switches so you can control the amount of light.
The most effective lighting brings out the fullest quality of the colors illuminated. If lighting levels are too low, there can be negative psychological effects, including depression.

For human comfort, a yellow-cast illumination is best. It is the color of brightness, and midway through the color progression from cool to warm.

To avoid glare, don’t place overhead lighting directly above computer screens, and don’t put a computer screen directly in front of a light source. That will cause eyestrain. Infact, overhead lighting and computer monitors just aren’t a great combination. Adding in a desk top lamp can do wonders to relieve eye strain and to create some additional warmth to a room that can typically feel cold and overly electronic. Some spaces work well with adjustable height task lamps, while others do great with more conventional styles. Try making the bottom of your lampshade just higher than the height of your monitor. It will go a long ways to producing the most light possible without overpowering your screen.

Energy guidelines are leading to new reduced-light levels in offices that are easier on the eyes. The most critical factor with lighting is the ability to control its brightness and intensity.