What happens to the intensity of light from a bulb if the distance from the bulb is doubled? As a laser beam travels across the length of a room,its intensity essentially remains constant. What geometrical characteristic of $LASER$ beam is responsible for the constant intensity which is missing in the case of light from the bulb?

(A) The intensity $(I)$ of light from a point source like a bulb follows the inverse square law,$I \propto \frac{1}{r^2}$. If the distance $(r)$ is doubled,the intensity becomes $\frac{1}{4}$ of its original value.
In contrast,a $LASER$ beam maintains constant intensity because it is highly collimated. The geometric characteristic responsible for this is its low divergence (highly parallel nature).
Key characteristics of $LASER$ light that contribute to this behavior are:
$(i)$ Highly collimated (low divergence)
$(ii)$ Monochromatic
$(iii)$ Coherent
$(iv)$ Unidirectional
These properties are absent in the light emitted by a bulb,which spreads out spherically.