The Literal Commandment
You shall charge the sons of Israel, that they bring you clear oil of beaten olives for the light, to make a lamp burn continually. In the tent of meeting, outside the veil which is before the testimony, Aaron and his sons shall keep it in order from evening to morning before the LORD; it shall be a perpetual statute throughout their generations for the sons of Israel. (Exodus 27:20-21)
The literal commandment is to keep the lamp (the menorah) lit continually.