Is it really the lighting or is the display weak and difficult to read even in the daytime? If it's the latter, there should be a contrast adjustment for that.
You probably need a new display, they punk out over time. Its American part #AC8065 list price is $1636.60. They use a LCD display which will degrade over time in the sun light.
No, the displays are not adjustable and not repairable unfortunatley. KR has the part for $963. (it was $762 last year--inflation I guess). I have 7 machines, so I keep one on the shelf.