The LCD on the new D610 I received becomes dim when I work on battery power. Like one bulb is burned out. I have tried various power management schemes but to no avail. Going back on AC power it brightens up to normal. Suggestions anyone.
That being said, you should be able to adjust the brightness and if it's the same as my D810 it should be toggled by the "fn" button on the left side and the Up and Down arrow keys. Otherwise have a look at the manual.
Of interest no manual came with this unit, only a quick reference guide that does not cover this minor issue. So I called technical support. It's a BIOS issue; going into the BIOS and selecting video there is a brightness slider; mine was at 3 and moving to 9 does the job. But I tried your suggestion (Fn and arrows) and that also works. My old Inspiron had a Dell user program installed and I could simply go there to find information. A manual also came with it. Don't know why this Latitude doesn't provide similar help.