In the Art of Electronics (Second edition), Section 2.02 (Transistor Switch), the book gives a circuit diagram
with a bulb rated 10V, 0.1 A, connected to the collector of a NPN transistor. The other end of the bulb is connected to constant voltage +10V. Then when current flows into the base, it says that we cannot blindly multiply \$I_B\$ by \$\beta\$, as a current of 0.1A would drive the voltage through the bulb to 10V, making collector voltage 0V. It also says that the collector voltage goes as low as possible, but still stays something around 0.05 - 0.2V above ground.
But then it comments that the bulb would glow in this case. But how? The voltage drop across the bulb is 9.95V at max, which is less than the rated 10V. Why does the bulb glow up?
Also, even if I assume that such low voltage differences do not affect the temperature of the filament, how does the book say that 0.1A would cause a 10V drop? I take the rating of the bulb to mean that when the bulb is glowing, a 10V drop would cause 0.1A (as resistance is almost fixed by the fixed temperature at that time). But how can this be stated even before the bulb is glowing?