Final answer:
The true statement is b, which states that lumen maintenance is the percentage of light produced by a lamp at mid-life. Lumen depreciation refers to the decrease in light output over time, and lumens are a more accurate measure of brightness than watts.
Step-by-step explanation:
The statement that is true regarding lumen maintenance and depreciation is b. Lumen maintenance is the percentage of light produced by a lamp at mid-life. This means that it is a measure of how well a lamp maintains its light output over time. Lumen depreciation refers to the gradual decrease in the light output of a lamp as it ages. Although it might seem like lumen depreciation and lumen maintenance would necessarily sum to 100%, that is not always the case due to how different types of lamps might behave. Therefore, statement c. is not universally correct and the accurate answer is b.
It is important to note that lumens serve as a measurement for light output, hence when shopping for light bulbs, lumens are a more precise method of comparing brightness rather than watts. Luminous efficacy, which is expressed in lumens per Watt, is an important factor in determining the efficiency of light bulbs. Modern LED light bulbs, for instance, can achieve much higher luminous efficacy than older incandescent bulbs, signifying greater efficiency.