Results of experiments are always open to interpretations. But in order to attribute an effect to one parameter, as the blue light in this case, it would be required that the parameter varies from the control to the other conditions tested.
Usually, experiments are designed to keep most parameters constant in it and vary just one parameter, and then results are analyzed based on the varying parameter. Attributing an effect to a parameter designed in the experimental method to be constant, as in this case, is hard to understand to me.
Maybe Im a little short minded and I cant see a casual link that others thinks is evident. In my humble opinion, again, I dont think that saying weight gain was due to differential blue content is a fair conclusion to experimental method and results of Oldmac. If some genius is able to identify by his results that the lighting was not fair, knows exactly what chamber had more blue in it, although designed to be equal, and negate the effect of the main variable parameter tested on final results, I must take off my hat. If its right. But it skip some logical steps and makes some assumptions in the distance, which I truly believe should be considered a "weak" link.
So, I dont discuss the effect blue has on cannabis growing. But saying that the results of an experiment designed to have equal amounts of blue are due the differences in blue, look as a effect of what psychologists call "focusing". A person is so focused on one topic that see it everywhere, and ends thinking almost anything is related to his obssesion, ignoring any logic in the process.
