That is exactly what he is saying. Because the plant has less light, it does not need as much of everything else.
When you watch Dr. Bruce, he tells you that the more light, the more of everything else you need. So when @Dirtbag changed to 12/12 he lost X amount of light but did not cut the nutes accordingly.
This is why you run veg at a lower light level so when you change to flower, you can up the light power to keep the plants needs stable.
Bingpot. Thanks, couldn't have said it better.
I will elaborate to help people understand it because It confused me at first too. The way Bruce explains it, think of photons as marbles falling from the sky. The plants catch these marbes and use them along with nutrients and Co2 to produce energy for growth. The more marbles it catches, the more nutrients and co2 it needs, and vice versa.
If you think of the marbles falling at a constant rate it's obvious the plant will catch more marbles in 18hrs than it will in 12, which means it has less need for nutrients in a 24hr day if the light level stays the same.
By increasing the light intensity during flower to match, or at least come close to the number of photons collected during the veg cycle means the plant should continue using roughly the same concentration of nutrients if all other parameters stay the same.
Knowing the Daily Light Interval or DLI let's you know roughly how much food and carbon dioxide is required to balance the plants inputs for optimal growth. It's a more important variable to consider than I ever.. considered? Lol.