I have a panda plant in my office facing west. I thought it was receiving adequate sunlight. However, my panda plant didn't grow very well and most of its leaves very thin and not fleshy. Does the glass absorb a great amount of sunshine? What can I do to ensure my panda plant has enough light indoors?
The amount of light lost through a piece of glass depends on several factors:
You're facing west, so you're only receiving half a day's light already. Assuming the windows are vertical, your minimum loss to reflection will be right at sunset when the light strikes the window at closest to 90°. Prior to sunset, every moment closer to noon you lose more to reflection because the light is striking at a greater angle. If you're in a city office building with reflective-coated windows that only get washed a few times a year, then they're almost always going to be dirty and losing light.
If you are in an office building (i.e. can't control the windows), and the windows are causing a lot of light loss, you don't have much choice but to relocate the plant to an environment where it can get more light (or get a different plant that is more tolerant to low-light environments). If you are located adjacent to a window, you can try placing the plant in the direct sunlight through the window to see if it gets better.
If you are in a setting where you can control the window (e.g. home office):