Hm, lots of "that" going on here, plus some bonus pronoun and meaning stuff. If you're not sure what to do with the word "that", check out
this crusty old article or
this YouTube video.
Quote:
A. equipment, such as lights, that are visible and must be turned on and off and underestimate that
The first "that" isn't quite right: it seems to be modifying "equipment," since "such as lights" is a self-contained little modifying phrase (an appositive, if you like grammar jargon), and the last chunk of the sentence is clearly discussing equipment in general, not just the lights. But there's a problem: "equipment... that are visible." Subject-verb fail.
What about the second "that"? It's a singular pronoun in this case, and I'd argue that it unambiguously refers back to "the amount of energy", since there's a super-clear parallel structure: "people tend to overestimate
the amount of energy used by equipment [that is visible]... and underestimate
that used by unobtrusive equipment..." And that seems completely fine: "people tend to... underestimate the amount of energy used by unobtrusive equipment" makes perfect sense.
But the first "that" is still a mess. Eliminate (A).
Quote:
B. equipment, such as lights, that are visible and must be turned on and off and underestimate it when
Same subject-verb error as in (A).
I'm also really not crazy about the use of "when" here: literally, they're saying that people underestimate the amount of energy used
at the moment when the energy is used by unobtrusive equipment. And that's not quite right: the underestimate is something that happens in general, and not at a specific moment in time. Either way, (B) is out.
Quote:
C. equipment, such as lights, that is visible and must be turned on and off and underestimate it when
"...equipment... that IS visible" is right, but we have the same "when" problem as in (B). Now that I think about it, I'm also not crazy about the "it" -- the pronoun is a long way from its antecedent, "the amount of energy." The pronoun "that" is much clearer in (A) or (D), because of the parallel structure.
If you wanted to be conservative and hang onto (C) at first, that's great -- I would do the same. But as we'll see in a moment, there's a much better option.
Quote:
D. visible equipment, such as lights, that must be turned on and off and underestimate that
Ooh, this looks great. No subject-verb issue, plus it's pleasantly succinct: "visible equipment... that must be turned on and off" is way better than "equipment that is visible and must be turned on and off." And as discussed above, "that" is a nice, clear pronoun. Keep (D).
Quote:
E. visible equipment, such as lights, that must be turned on and off and underestimate it when
The first part of the underlined portion is nice, but the last chunk "and underestimate it when" is a little bit shaky, both in terms of the pronoun agreement and the meaning of the word "when", as discussed above. (D) is clearly a better choice.