I thought henna was for making hair red. And bnc, Are you talking about sun-in? I heard it works but it can be really drying and can turn hair brassy.
I've done the lemon juice before. I'd dilute it and spray it on before going out in the sun. It worked but it could be drying so condition moisturize. I recommend diluting it with chamomile tea because it helps with lightening too.
Have you heard of honey lightening? You could google it up and I REALLY recommend looking at this thread at a forum in the internet dedicated to it. I can search it up for you if you want. It's supposed to work gradually and it's not drying at all. It can even be considered conditioning.
There's also cinnamon. Some people sprinkle it on and some people mix it with their conditioner or do a deep treatment with it. It lightens but may also add a bit of red. Btw I recommend diluting it and doing the conditioner method because it tingles. But if you add too much it can REALLY tingle.
There's also the 3% hydrogen peroxide. Diluted please. But it can be drying.
I heard olive oil can lighten hair in the sun too but I think it takes a while. But it's a way to start small.. Like using it as a sealer.