bjtsaturationtransistors
As you can see on the datasheet below for the 2n2222a NPN transistor, the "Collector-Emitter Saturation Voltage" and "Base-Emitter Saturation Voltage" are defined respectively as 0.3 to 1.0 and 1.2 to 2.0. I believe I understand transistor saturation, but whats the difference between Collector-Emitter Saturation and Base-Emitter Saturation?
There really isn't a single '2N2222' transistor, since each manufacturer just seems to use XYZ_2N2222 as a part number for a generic 'NPN silicon amplifier transistor'.
Hence the 2N2222 pin-out is sadly not standardized. Most 2N2222s have the orientation which your diagram shows, where if the flat side is facing you, the pins are E-B-C respectively. However, some manufacturers have the pins going C-B-E for the TO-92 package. For example, the ON Semi P2N2222A variant: datasheet
Rule 1 isn't a "good idea", it isn't a "guideline", it is a fundamental tenet of transistor physics. If for any reason (during normal usage) it is unable to hold then the circuit will not operate.
As for the lamp, it is a purely resistive element. It should have 10V across it, but thanks to the transistor it won't. So the transistor gets 0.2V and the lamp gets 9.8V and reality is saved.
Best Answer
Vce(sat) is the voltage measured at the collector relative to the emitter under the specified conditions (say 150mA of collector current flowing, and 15mA of base current applied (forced beta of 10, obtained by dividing Ic by Ib thus 150 over 15 mA).
Vbe(sat) is the voltage measured at the base relative to the emitter under the specified conditions, as above.
So if you are wanting to switch a 150mA load under those conditions with (say) a 10V input, you will use the latter number to determine the required resistor value to get the minimum base current needed (and ensure you don't exceed any maximum if the minimum Vbe(sat) is specified).