@sean2masaaki, With science experiments we know that children have a passion for learning. As parents we will be proud when children insightfully discover new things and can provide deeper understanding. Through this creative learning method, students will learn better. Students not only learn cognitively but are also invited to actively learn while doing.
From the experiment of the lamp being able to light up with salt water, children can find knowledge that salt water is a conductor. We just need to give a little explanation that salt contains minerals that can be a conductor. Thus, children know that electricity does not only flow through cables. Electricity can be channeled through water which is a conductor.
As a reader, I can only give #comment that it turns out that your child has a high enthusiasm for learning. This is a sign that he has an interest in science. As a parent, you should be proud to have a child who can practice in learning so that he can understand and comprehend what is being studied. He not only reads theoretically but knows very well through the experiments he does.
This is worth emulating by all children so that every child can find an interesting experience in learning and avoid boredom just studying behind a desk and paper or books.

Warm regard from Indonesia
@rokhani