Question

The ratio between the reflected to the incident energy on a surface at a particular wavelength gives the ............................. of the surface.

• A. spectral reflectance
• B. spectral transmittance
• C. spectral radiance
• D. spectral irradiance

Hint:

Think “R–T–A” at each wavelength: $\rho_\lambda$ (reflect), $\tau_\lambda$ (transmit), $\alpha_\lambda$ (absorb) with $\rho_\lambda+\tau_\lambda+\alpha_\lambda=1$ (for non-emitting, non-lasing samples).

Answer 1

The Correct Option is A

At wavelength $\lambda$, spectral reflectance $\rho_\lambda$ is defined as
\[ \rho_\lambda=\frac{\text{reflected radiant energy (or flux) at }\lambda}{\text{incident radiant energy (or flux) at }\lambda}. \] Spectral transmittance $\tau_\lambda$ uses transmitted energy in the numerator; spectral irradiance $E_\lambda$ is incident power per unit area per unit wavelength; spectral radiance $L_\lambda$ is power per unit area–solid-angle–wavelength. Hence the ratio asked is spectral reflectance.