If you mean the HS200 switch blinks, drops, and restarts, it's probably a wiring problem. Check for lose connections, esp the white/neutral wire. If it's not that then you may have "power through fixture" wiring and the HS200 may not work there.

The problem is the actual light I want to control, not the light on switch. Is there a way to verify if my wire is "power through fixture"? If I don't connect the white wire, the symptom is the same.

MikeP_AutomationManager wrote

If you mean the HS200 switch blinks, drops, and restarts, it's probably a wiring problem. Check for lose connections, esp the white/neutral wire. If it's not that then you may have "power through fixture" wiring and the HS200 may not work there.

I am having this same problem as HenryYao. I have a power through fixture. Can you tell me why this means I cannot use the HS200? Or if there is a workaround, can you try explaining it? Thank you so much!

Power through fixture will look like http://www.buildmyowncabin.com/electrical/wiring-switch-power-into-light.html. The live wire will be the white and if done properly should have a black mark or tape on it at the switch end. The problem is there is no neutral line available as the black at the switch goes back through the load before returning to neutral white (and there's only 2 wires available in the box rather than the 3 needed - line in, load out, and neutral). You'll need to run a separate neutral wire to the switch to make it work properly.

It's an electrical code violation to wire the HS200 blacks to each of the incoming wires and the HS200 white to ground.

Has anyone made the HS200 work with a power-through switch? I live in a condo and running another wire isn't going to be an option for me. I'd have to get an electrician because I am not certified for electrical work.

Trust me, even if you feel that you can modify the wiring, this kind of DIY work will violate condo bylaws and insurance policies.

HenryYao wrote

The problem is the actual light I want to control, not the light on switch. Is there a way to verify if my wire is "power through fixture"? If I don't connect the white wire, the symptom is the same.

The white line on the switch is the neutral line. The two live lines and one neutral line are all indispensable.
I found a FAQ which tells me more details: http://www.tp-link.com/en/faq-1128.html