There's also a note at the very very bottom of the article that "it seems that the energy issue might be reduced by the introduction of a new generation of LED

There's also a note at the very very bottom of the article that "it seems that the energy issue might be reduced by the introduction of a new generation of LED grow lights which reduce the energy required by just providing the plants with the part of the radiation spectrum that they require for growth." It's not clear whether this is from Monbiot or the person who provided the numbers, but either way I invite you to consider the changes in quality, availability and pricing for standard LED bulbs as replacements for incandescent bulbs in the six years since that article was published.