Can I disable the key lighting on LK-280?

Yes, it is possible for you to disable the key lighting. To do this, hold the FUNCTION/KEY LIGHT button until "Keylight" appears on the display, and then you can press the [-] key to turn it off from there.

This is the same procedure described on page E-11 of the LK-270 manual, but was omitted from the LK-280 manual.