Activate a Light viewport. > Viewport navigation controls > Light Hotspot
The streetlight has a narrow hotspot but a wide falloff area.
Widening the hotspot creates a brighter light.
Light Hotspot lets you adjust the angle of a light's hotspot. This button replaces the Zoom All button when a light viewport is active.
Click this button, then move the mouse in the light viewport to make the cone of the hotspot narrower or wider (the hotspot cone is shown in blue, the falloff cone is in gray).
Hold down the CTRL key while moving the mouse to lock the initial angle separation of the hotspot and falloff cones.
You can't adjust the hotspot larger than the falloff, because that would change the falloff value. Likewise, when you reduce the falloff, it stops at the hotspot size.
To override the separation of the hotspot and falloff parameters and cause the parameters to affect each other, hold down the SHIFT key.
Procedure
To change a light's hotspot:
Set up a Perspective viewport so you can see the light in 3D space.
Activate a Light viewport.
Press H to display the Select Objects dialog. Select the light.
The light and its cones should be visible in the Perspective viewport.
Click Light Hotspot.
The button turns green when it is on.
Drag in the Light viewport to change the hotspot angle.
The blue hotspot cone expands and contracts as you drag.
Drag down to widen (increase) the hotspot angle and illuminate more of the scene.
The hotspot grows inside the falloff as its angle increases. By default, the hotspot can be no larger than the falloff cone.
Hold down SHIFT as you drag to override the default. This lets the falloff cone increase in size as you increase the size of the hotspot cone.
Drag up to narrow (decrease) the hotspot angle and illuminate less of the scene.
Hold down CTRL as you drag to lock the initial angle separation of the hotspot and falloff cones.
Press ESC or right-click to turn off the button.