Not only light but movement of air and the noise of the wind in the trees makes me feel more open.
Daylight bulbs and ones that don't put off much heat. Daylight is a cool white, not warm white. So for the walls, I'd suggest very light taupe, rather than cream.
The ambient light is important: this is general lighting reflecting off the ceiling (it must be light to reflect light). Then there's task lighting which would be over the work stations. Sounds like you have task lighting. Maybe you need more general lighting.