The expression "sexual frustration" is an attempt to "vulgarize" or if you prefer, to made in a more accessible word, very techical scientific data to explain the hormonal respond induce by the spectrum of the sun going lower in the sky that produce a shift in the spectrum to the "reddish" one because it have to pass through more thick layer of the atmosphère and the shorter "blueish" spectrum are less able to pass through.
But, yes, it's not totally accurate since plant do not have "human feeling", however, it's a widely repend expression to express and attempt to explain to the public, the hormonal respond triggering. You can achieved that by elevate the distance between the canopy and the light since the blue spectrum, that have shorter wavelengths, are fading faster as distance is greater and that, I think that the relation as a greater exponential lost than the red spectrum shift, I know I have this some where, but for now, it do not come in my memory, lol , I am getting old, lol . ..
Anyway, I stick to my explanation and that is standing to the shorter light exposition too , that, in combination of the redier spectrum, will induce the hormonal respond to be greater. @Majiktoker @Countryboyjvd1971