I have 3 of the same strips and I have no idea whatsoever how to power them. They light up when I use a 200ma power supply. My main problem is trying to figure out how much power they use in watts. If they use more watts than what I already have then it really doesn't matter that they are LEDs. (wanted to use under my kitchen cabinets)
I'm not surprised that they were glowing, even at 200mA. Did you measure both the current and the voltage to be sure that it was 200mA and 12V? It might be possible that you were overloading the power supply which resulted ion less than 12V being delivered to the LEDs. That would result in reduced brightness. Basically, the LEDs were not working on full power.
To truly measure the brightness and power consumption you really need a power supply which is capable of providing 12V at a current greater than what the LEDs will need. That way you can take accurate measurements of the current consumption.
As far as measuring light output, that is another story altogether.

Usually light output is measured at some predefined specific distance and angle from the light source. Of course moving the meter around will change the reading.