Which of the following is not part of the classification of an incandescent lamp?

The classification of an incandescent lamp typically involves several key characteristics, such as wattage, color temperature, and type of filament, which directly impact its performance and application. Wattage indicates how much energy the bulb consumes and relates to its brightness. Color temperature describes the appearance of the light emitted, whether it is warm or cool in tone, which is essential for aesthetic and functional lighting considerations. The type of filament plays a crucial role in luminescence and efficiency; for example, a tungsten filament is commonly used in incandescent lamps to provide a warm light.

While size might influence the fitting or the physical space where the lamp could be used, it does not directly pertain to the classification that affects performance or behavior of the lamp itself in terms of light output or efficiency. Therefore, size is not typically included in the critical classifications that define the operational characteristics of an incandescent lamp, making it the correct answer for this question.