Think of an LED like a water-fed fountain; the brightness is the height of the water, and the current is the flow rate of water. Once the pressure (source voltage) is high enough, the flow becomes steady, and the fountain height stays constant.

I-B-I: Intensity is Brightness dependent on Intensity of current.

An LED functions based on the principle of electroluminescence. When a forward bias is applied, electrons from the n-side and holes from the p-side recombine in the p-n junction, releasing energy in the form of photons. The intensity of light ($I_{L}$) is governed by the forward current ($I_{F}$), where $I_{F} = \frac{V_{source} - V_{diode}}{R}$. As $V_{source}$ becomes much larger than $V_{diode}$, the impact of minor fluctuations in $V_{diode}$ on $I_{F}$ becomes negligible.

In competitive exams, always remember that diodes are non-ohmic conductors; never connect an LED directly to a voltage source without a series resistor to prevent excessive current flow.