The product that has its heavy-metal impurities listed (proudly) is supposed to contain less of these impurities than the products where this information is "skipped" So, you are not feeding with more lead than with any other mineral fertilizer with similar ingredients.
UV light however really speeds up flowering and maturation of resin. The same clone flowered outdoors under the sun is ready in fewer weeks than when flowered indoors.
Not arguing but using high Kelvin or blue light in flower quickens the maturation also. My 10,00 K bulbs are called Finisher.