judging health of plants

Recently I did a major trimming of my plants and found that for some stem plants, although the top of the plants seems to be healthy , the lower part of the stems are almost always "botak", is this normal as the bottom part of the plants are not receiving enough lights, or it could be better?

ya... this is also the problem for me. I duno how to maintain the btm part , i guess this is not normal.

Is it light intensity not enuf to penetrate into the bottom part?

It is extremely common for the leaves in the lower sections to yellow and drop off, especially when you plant them thickly for them to form a lush top canopy.

What you need to look out for is that, although it is ok for the lower part to not have leaves, the stem at the lower section should not be getting soft and appear to become weak. Do conduct checks that the stems are strong and thick.

Any websites to refer?