I agree! The developer is not what actually lightens your hair, the bleach is! If you do not want to bleach your hair, you can always book a consultation at your local salon (its usually free). The hair stylist can determine if they can use color only to lighten your hair
lcjames is correct, you will need some kind of dye or coloring to add to the developer which causes the lightening. What color is your hair now and how light are you going? I always recommend bleaching and lightening to professionals if you are going more than 2 shades lighter!