Unlike 12464-1:2002 standard, 12461-1:2011 standard defines the minimum number of measuring points and the dimensions of the grid cells for the different task areas. Illuminance grids are defined according to UNI EN 12193 standard criteria and have the following characteristics:

The ratio of length to width of the grid cells ranges between 0.5 and 2.

Measuring points correspond to the barycentre of each cell.

The maximum size of a cell is calculated using the following formula:

p=0.2x5log10(d)

Where “p” is the grid cell size and can reach a maximum of 10m and “d” is the longer dimension of the area if the ratio of the longer to the shorter side is less than 2, otherwise “d” is the shorter dimension. “n” represents the total number of measuring points along the dimension “d”. It is the closest whole number greater than the ratio:

n= d/p

“p” is the result of the ratio:

p=d/n

The measuring points along the other side of the grid are calculated in the same way.

The ratio of one side to the other must be as close to 1 as possible. Illuminance grids must not include a band, at least 0.5m wide, from the walls unless the visual task is not carried out at a lower distance.