@Gingernook 

Hi, thanks for posting question here.

I am afraid the situation you subscribe is normal.

Only TP-Link router and TP-Link powerline devices can set up Onemesh network if they support Onemesh feature.

  @Gingernook 

Hi, is it a smart bulb? If you connect the bulb to your main router and the bulb can still be controlled via its app when you are not at home, that means your bulb can be connected via cloud. I am not sure the model of your bulb, for TP-Link smart bulbs, it works so.

I understand your needs, however the powerline devices just make up a basic network, your device can get internet access when it is connected to the powerline unit. The internet source is your main router. So it is suggested to check the settings of your main router, like firewall and so on.

It is also suggested to contact technical support of your bulbs for some advice.