These would make interesting experiments, (if you have the plants to spare)! I always like to see experiments, because this is how we advance our abilities to best grow the plants.
It's not always best to rely on "common knowledge". Sometimes common knowledge can be a myth, other times it is a goldmine!
In this case, common knowledge states that plants must have a dark period in order to "respire": this is the opposite of photosynthesis where plants take in carbon dioxide. In respiration, they take in oxygen, give off CO2, and also undergo other processes which may or may not be needful to continued good growth. It's easy to assume they are, but until tested, these are just assumptions. How long this dark period may need to be is also open to question by a good controlled experiment.
It is also said that blacklight does nothing for the plants, since the light spectrum is one the plants cannot use. I think some experiments were done using only black light for the plants, and they did not live. Would an addition of blacklight have any effect, positive or negative? You would need to grow identical plants in identical conditions except for the addition of the black light, and observe any significant differences in growth. An experiment like this would need to run for a year (the length of time needed to be able to note any difference), but it would be very valuable, since it would answer this question in a very solid way.
