LED is constructed from $$Ga - As - P$$ semiconducting material. The energy gap of this LED is 1.9 eV. Calculate the wavelength of light emitted and its colour. $$h = 6.63 \times 10^{-34}$$ J s and $$c = 3 \times 10^8$$ m s$$^{-1}$$

The wavelength of light emitted by an LED is related to its energy gap by the relation $$E = \frac{hc}{\lambda}$$, which gives $$\lambda = \frac{hc}{E}$$.

Substituting the given values: $$h = 6.63 \times 10^{-34}$$ J s, $$c = 3 \times 10^8$$ m/s, and $$E = 1.9$$ eV $$= 1.9 \times 1.6 \times 10^{-19}$$ J $$= 3.04 \times 10^{-19}$$ J.

$$\lambda = \frac{6.63 \times 10^{-34} \times 3 \times 10^8}{3.04 \times 10^{-19}} = \frac{19.89 \times 10^{-26}}{3.04 \times 10^{-19}} = 6.54 \times 10^{-7} \text{ m} = 654 \text{ nm}$$.

A wavelength of 654 nm falls in the red region of the visible spectrum (approximately 620-750 nm).

Hence the correct answer is Option 1: 654 nm and red colour.