I've dyed my hair probably more than most. It would be accurate to say that for a time, I was addicted. There isn't much along the lines of hair coloring that I have not tried. I am fortunate to have *very* resilient hair. By all accounts I shouldn't even have hair anymore, lol. This being said, I can probably help if you are considering dye. I have dyed over henna a few times. My natural is also a light brown. What I would recommend to begin getting rid of the red is to go over with a light-medium ash brown. Use a more gentle brand like Natural Match. You will likely need to do at least two applications. Your best bet may be to go for light ash, and if you need it, light ash a week or more later, too light is easier to correct than too dark. The reason for "ash" is that you will be mixing whatever dye you choose with the red you already have. You need to think of it like mixing two colors to form the goal color. Henna red/orange mixed with an ash shade will result in reduced red. Non ash shades would render a more golden brown result. Sorry, this is very long. I hope it was helpful. I'd be happy to talk more about it if you like.