This test will not be good for your Li-Ion cell.
Voltage sag occurs with a normal load, and is typically 0.5V - 0.75V. When the load is removed, the voltage 'bounces back' up to a resting voltage.
What you are doing will take your protected cell right down to the low-voltage cut-off point, as you would expect, but the problem is that at 10 lm it is using very little power, so there will be no voltage sag to speak of.
The cell will therefore not rebound back up above 3.0V, which means it will have been badly over-discharged. Its cycle life will have been reduced, and you will have to be very careful when recharging it.