U-shaped fluorescent lamps are primarily used in __ luminaires (lighting fixtures). Select one: a. \( 1^{\prime} \times 4^{\prime} \) b. \( 2^{\prime} \times 2^{\prime} \) c. \( 2^{\prime} \times 4^{\prime} \) d. \( 1^{\prime} \times 8^{\prime} \)

To determine which luminaires are primarily used with U-shaped fluorescent lamps, we can analyze the options provided: 1. **\( 1^{\prime} \times 4^{\prime} \)**: This size is relatively small and may not be the most common for U-shaped lamps. 2. **\( 2^{\prime} \times 2^{\prime} \)**: This is a square fixture, which could accommodate U-shaped lamps, but it is not the most typical size. 3. **\( 2^{\prime} \times 4^{\prime} \)**: This is a longer fixture that is commonly used for U-shaped fluorescent lamps, as it provides enough space for the U-shape to fit properly. 4. **\( 1^{\prime} \times 8^{\prime} \)**: This is a very long fixture, which is less common for U-shaped lamps. Based on the typical applications of U-shaped fluorescent lamps, the most suitable option is: **c. \( 2^{\prime} \times 4^{\prime} \)**. This size is commonly used in commercial and industrial lighting applications where U-shaped fluorescent lamps are installed.