Custom Curve allows you to tailor the falloff exactly according to your needs, as explained in the following steps:
In the Lamp subpanel, click on the button beneath Falloff; next, click on the button labeled Inverse Square, and select Custom Curve from the menu.
Set Distance to
47, located in the button below Custom Curve.Scroll down to the Falloff Curve subpanel. Click on the triangle to the left of the Falloff curve to open the subpanel.
Note that there are three vertical grid lines and three horizontal grid lines. The line that goes diagonally from upper left to lower right is a Bézier curve. When you click on that line, a control point is put there, and you can move that control point to change the shape of that line.
Move the mouse over the diagonal line. Near the leftmost vertical grid line, press the LMB and drag the curve down so that the control point is at the intersection of the center horizontal grid line and the leftmost vertical...