A lamp is rated at 12V,6W. What does this mean? How much current is passing through the lamp when it is connected to a 12v supply?
V (stands for volt) is the units for voltage and W (stands for watts) is the unit of power. A lamp that is rated as 12 V, 6 W will draw 6 W of power when connected at 12 V supply. The lamp will work most efficiently at 12 V supply. If connected across a higher voltage, it may get damaged or may have lesser life. If connected across a lower voltage, it will provide lesser brightness.
Power, voltage and current are related by the following expression:
P = V x I
where, P is the power, V is the voltage and I is the current.
In this case, P = 6 W and V = 12 V
thus, I = P / V = 6 W / 12 V = 0.5 A or 500 mA
Thus, a current of 0.5 A or 500 mA will pass through the lamp when it is connected to a supply of 12 V.
Hope this helps.