Which of the following describes a more efficient lamp?

Lamp efficiency in EDGE is a key factor in reducing energy consumption for lighting, a critical green building design strategy. The EDGE User Guide defines lamp efficiency: "In EDGE, a more efficient lamp is one that provides higher lumens per watt, meaning it produces more light output (lumens) for the same electrical input (watts). This metric, known as luminous efficacy, is used to evaluate lighting efficiency measures like EEM22 - Efficient Lighting for Internal Areas" (EDGE User Guide, Section 4.4: Lighting Efficiency Measures). Option A, more lumens/watt, directly aligns with this definition, as it indicates greater efficiency in converting electricity to light. Option B (lower watts/m²) refers to lighting power density, which is a design metric, not a lamp characteristic: "Watts/m² is a measure of lighting power density for a space, not the efficiency of an individual lamp" (EDGE Methodology Report Version 2.0, Section 5.4: Lighting Calculations). Option C (longer life) relates to durability, not efficiency: "Lamp life affects maintenance costs but is not a direct measure of energy efficiency in EDGE" (EDGE User Guide, Section 4.4: Lighting Efficiency Measures). Option D (lower wattage) alone does not indicate efficiency, as a lamp with lower wattage but poor light output would be less efficient: "Lower wattage must be paired with adequate lumens to improve efficiency" (EDGE Methodology Report Version 2.0, Section 5.4: Lighting Calculations). Thus, more lumens/watt (Option A) describes a more efficient lamp.