When you hit a certain light level, the limiting nutrient becomes Carbon...coming from Carbon Dioxide gas. If the plants can't breath
CO2, they can't consume nitrate and phosphate (the two macronutrients that are also responsible for algae blooms).
So without
CO2 the plants get stunted, and you have all this extra 'food' available, so the algae takes advantage of this.
Plants also emit allelochemicals (i totally misspelled that) which inhibit algae growth. its my personal theory that stunted plants don't produce these chemicals...making algae blooms that much more likely.
When you add strong lighting to a tank, the plants will go nuts for a week, then they have no stored carbon left. Then algae shows up, and its an uphill fight to get rid of it. Adding consistent levels of
CO2 kick the plants back into gear, and the algae will subside on its own, provided you have a proper ratio of nitrates to phosphates (10:1 is a common ratio, 15:1 also works), enough potassium (around 15-20ppm), and your trace ferts are good.