One of the biggest causes of confusion and disagreement in the world of grow lighting is the word "brightness". The problem is that we constantly use the word colloquially to describe how things "appear" to us – it's a bright sunny day, that bulb is a bit bright, etc. It is no way a scientific definition of light intensity – the number of photons hitting a specific area over time – and ignores wavelengths of light that humans are less sensitive to.