From my photography experience, there are three aspects of light to consider for any scene--your office included. They are:
- Quantity -- how much light there is (measured in lumens or lux)
- Quality -- how direct or diffuse the light is
- Color -- the color balance (measured in degrees Kelvin)
With photography, there's two standard color balances to be concerned with: tungsten balance and daylight balance. Tungsten is around 3400K, give or take a bit. Daylight is around 6500K. Based on the research other answers pointed to, you really want daylight balanced lighting.
That leaves the other two aspects to consider. How much light you need, and how it shines in the scene. I can use these to explain why the halogen is bad. Halogens are very high brightness, with a pin point source. That means your shadows are going to be really hard and your reflections really sharp. That's bad for prolonged use because your eyes will get fatigued dealing with the sharp contrasts.
- You want a larger light source to reduce contrast and provide a more even light. Both LED lighting and fluorescent lighting provide this, but the effect of a larger light can also be done using some sort of diffuser. A white acetate on the top and bottom of your lamp gives the effect of a larger light source than originally exists.
- You want enough light so that your eyes can focus for long periods, but not so much that it causes problems seeing the screen. A dark room is only effective if you don't have to reference printed materials. You want just enough light so that it is comfortable reading the printed materials, but not much more than that. Too much light and you have to squint to limit it. That's why it's such a pain to read outside.