Which lamp has the shortest MOL?

The option indicating Par20 lamps as having the shortest Maximum Overall Length (MOL) is correct due to the design specifications of the various lamp types in question. The Par20 lamp is typically smaller in size compared to the other options listed.

PAR lamps (parabolic aluminized reflector lamps) have distinct characteristics based on their design purpose and physical dimensions. A Par20 lamp generally has a diameter of approximately 2.5 inches and a shorter overall length, making it suitable for applications where space is limited and a more compact lighting solution is needed.

In contrast, options such as BR30, R20, and Par30 lamps have larger diameters and longer lengths. The BR30 and R20 lamps, for instance, while both designed for different lighting effects, still fall within a larger overall size category compared to the Par20. The Par30 lamp, being larger than the Par20 with a diameter of about 3.75 inches, also inherently has a longer overall length.

Therefore, the inherent dimensions and design specifications of the Par20 lamp establish it as the option with the shortest Maximum Overall Length among the listed choices.