I have the following sentence:
Conventional light bulbs will be replaced with energy-saving alternatives by 2020.
According to my book, the next sentence is also correct:
Conventional light bulbs are to be replaced with energy-saving alternatives by 2020.
But I was taught that in the sentences referring to the future with by (date)
we use Future Perfect.
I would write as follows:
Conventional light bulbs will have been replaced with energy-saving alternatives by 2020.
Am I right? What is the difference in meaning between these three sentences? Thanks in advance!