You say that you can't see the flicker? I can tell you how you can see it.
This can get long winded and technical so I am going to try to keep it really simple. This works in the US, not sure about other places.
When Electricity is generated it is produced on 2 sides of the generator, both these "legs" of the power are delivered to your home by the power company and then when your home is wired the legs are used randomly throughout your home. If you sit in a room for a long time that is lit by only 1 incessant lamp doing something like reading then exit that room and go to another room that is again lit one single incessant lamp on the opposite power leg you will notice a slight flicker. You can also sometimes see this effect if you step outside on a dark night with no streetlights on.
Why? Your brain does a lot of really cool things and this is one of them, the light on one leg actually dims ever so slightly 60 times a second, you don't notice because it is slight, and happens quickly. Your brain notices but doesn't tell you and just adjusts to process visual information when it has the most light, this happens over time so you don't notice it. When you move to another space where the light is dimmest when the light in the space you were in is brightest you notice a slight flickering as your brain is trying to catch up and adjust. If you live all your life in 60Hz and are sudden thrust into 50Hz you will notice this as well because you have not developed the timing in tour brain for 50Hz, it will come eventually. If you live in a place where you see both 60 and 50Hz all the time you develop the timing for both.
Oh and if you made it through all that, why not just make some test strips?