Design voltage with respect to an incandescent lamp means:
(1) The voltage marked as the intended operating voltage;
(2) The mid-point of the voltage range if the lamp is marked with a voltage range; or
(3) 120 V if the lamp is not marked with a voltage or voltage range.
10 CFR § 430.2
For purposes of this part, words shall be defined as provided for in section 321 of the Act and as follows -