How many fixtures need to be installed in the classroom?

Good afternoon, according to SanPiN 2.4.2. 2821-10 clause 7.2.4 illumination at the level of tables should be in the range of 300-500 Lux. If we calculate the illumination roughly according to the area, then each lamp produces 2800 Lm, 1 lux is 1lm / 1 m², with an area of ​​700 m² for illumination of 300 Lx it is necessary to provide a total luminous flux (Lx * m²) of 210,000 Lm. This means that you need 210000/2800 = 75 of these fixtures. But this is a very rough calculation, although approximately the same amount will be installed, I believe - every 2 meters in the lamp in 2 rows ...