Mix light brown sugar, granulated sugar, heavy cream, butter, water and salt in a heavy-bottomed saucepan. Cook over low heat, stirring constantly with a wooden spoon, until sugar dissolves. Stir in pecans and cook over medium heat until mixture reaches the soft ball stage, 238 to 240 degrees F on a candy thermometer. If you spoon a drop of boiling syrup into a cup of ice water, it will form a soft ball that flattens easily between your fingers.
Remove pan from heat and stir rapidly until mixture thickens. Drop pralines by the spoonfuls, 1-inch apart onto parchment paper-lined baking sheets. Let cool completely until firm. Store in an airtight container.