Color Temperature, Eye Strain and Headache
First link with an explanation about color temperature, too long to copy here:
http://www.osram.nl/media/resource/hires/333565/light-can-be-white-en.pdf

Basically...


fluorescent tubes x30 are equivalent to halogen light. I installed them in my living room because I like warm light, but warm white (2700 K) was too warm. It will not tire your eyes and won't make you feel too awake at night, so you fall asleep normally
tubes x40 are cheap industrial lighting, warmer than the light outside, but not so warm to make your place feel "home" (yeah this is the best I can go to be short)
tubes x54 are equivalent to outside light, in a bright but not sky-blue day. Not common.
tubes x65 are basically almost blue and equivalent to a day when the sky is without cloud, blue. Not suitable.


The "x" above can be 6, 8, 9. For industrial you use 6, better luminous efficiency, for normal use 8, for specialised work (photo editing/printing studio, expositions, ...) and 8 for the rest.

If you have 840 you should be fine, it's very common. 830 is also common, in my company this is what we use in the offices. I can clearly see that, when the light is on during the day, the office walls close to the entrance appear more reddish/yellowish than the walls closer to the window. But it doesn't matter.

Color-wise you are fine (check also the PDF linked).

If you have old ballasts, they run at 100 Hz and you may unconsciously see some flickering. Better replace them with electronic ballasts. The former produce one or two flashes when you turn the tubes on, the latter make the tubes produce at the first shot the light (do the test in the morning when the tube is cold).

If you have an electronic ballast, and you already have a tube 8(35/40/54), then the source of your eyestrain is something else.

Check the monitor, reduce sources of reflections (or of diffused glare if it is a matte display, as it should be, in general, for office work).

Check the distance between eyes and monitor: it should be at arm-length distance.

Take breaks and look around, outside the window, etc, even 10 seconds every 10 minutes help a LOT, use Workrave for Windows or AntiRSI for Mac.