How do I lighten my natural dark blond hair?

Hey.

I am a 20 year old guy with natural blond hair. When I was younger my hair was a platinum blond but now it has darkened to a brownish blond/dark blond. Some of the hair roots on my head are still a platinum blond but after a very short distance my hair darkens. I am looking around for ways to lighten up my hair to a brighter blond. I do not want platinum blond but just a brighter/lighter natural blond; I think the term is ash blond.

I have tried some things. One is sitting out in the sun for about 20-45 mins each day, when I can. I usually go out in the afternoon. To understand the sun strength for me I live in CT, which is in the northeast of the US, in an inland rural area. I have been told the sun makes my hair blonder.

I have also recently tried a hair lightener called “Sun-In.” Sun-In is a spray on lightener that gives the hair a blonder look. The change in color is introduced by heat when the spray is dried either by the sun or a blow-dryer. The color change is permanent but after a few weeks the color dulls a bit. This works alright but the hair only looks blonder in certain lights. I do not use a lot of this lightener; basically I spray it all over my hair after a haircut which is about once a month.

The shampoo I use is Sheer Blonde Highlight Activating Moisturizing Shampoo and Sheer Blonde Glistening Perfection Moisturizing Conditioner. I have used this for over a year. It makes my hair nice and soft but it has not really brightened my hair color.

So I am looking for help in getting my hair to a lighter blond while keeping it healthy. Is there a certain shampoo/conditioner I should use? Is the Sun-In good idea? Is going out in the sun a good idea? I have read about ARTec Colorist Collection and was wondering if I should try this shampoo instead of my current one.

Any help is appreciated.