My hair is dark brown/black, I want to make it lighter, but no more than 1 or 2 tones, hopefully, but I don't want to color it. I've read lemon could do the trick but also that I could end up with my hair orange, is that tru? If I cut some hair and apply lemon to it, then leave it in the sun, is that a proper test of how it will end up? Is there any other way?

You could try using a light color shampoo. And the lemon will Not turn your hair orange.
Definitely being out in the sun will make your hair lighter on its own.
I know you don't want to color your hair, but if you wanted to use a semi or demi color it will lighten it and not be permant. Last a few weeks to few months.
You could try that test, it wuoldnt hurt, but I don't think you would be able to tell much difference in a little strand of hair. GoodLuck.