Obviously it difficult to work with such large numbers, so growers started using the more manageable term “micromole” (also written as μmole or micro-mole) rather than the cumbersome 602 quadrillion.
We will get to the complicated formal definition at the end of this article but for horticultural lighting it is quite simple – a micromole is a number of photons. Actually, it is a very large number of photons. 602 quadrillion to be exact. That’s 602 followed by 15 zeroes.