transmittance_calculator

arte.photometry.transmittance_calculator.attenuation_coefficient_calculator(l1, l2, t1, t2)

Compute attenuation coefficient of a glass from external transmittance data of two different values of thickness. The computation is based on the equation for the external transmittance of a glass:

T = (1 - R)**2 * exp(-a * l)

where R is the reflectance, a is the attenuation coefficient and l is the thickness of the glass. If we consider two different values of thickness, thus of transmittance, we can compute the ratio between the transmittances:

T1 / T2 = exp(-a * (l1 - l2))

and from this equation we can derive the attenuation coefficient as:

a = (lnT2 - lnT1) / (l1 - l2)

arte.photometry.transmittance_calculator.external_transmittance_calculator(l1, l2, t1, a)

Use external transmittance data of a glass with thickness l2 to compute external transmittance of a same glass but with different thickness l1. The computation is based on the equation for the external transmittance:

T = (1 - R)**2 * exp(-a * l)

where R is the reflectance, a is the attenuation coefficient and l is the thickness of the glass. If we consider two different values of thickness, thus of transmittance, we can compute the unknown transmittance T2 as:

T2 = T1 * exp(-a * (l2 - l1))

arte.photometry.transmittance_calculator.interface_glass_to_glass(n1, n2)

Compute reflectance of a glass, considering the refractive index of the medium the light is coming from (n1) and the refractive index of the glass (n2)

arte.photometry.transmittance_calculator.internal_transmittance_calculator(l1, l2, t1)

Use internal transmittance data t1 of a glass with thickness l1 to compute internal transmittance t2 of a same glass but with different thickness l2. The transmittance is computed with the following equation:

t2 = t1**(l2/l1)

arte.photometry.transmittance_calculator.internal_transmittance_from_external_one(t_ext1, t_ext2, l1, l2)

Compute the internal transmittance of a substrate with thickness = l2, knowing the external transmittances for both l1 and l2.

Considering that the ratio between external transmittances and internal ones is the same:

T_ext(l1) / T_ext(l2) = ((1 - R)**2 * exp(-a * l1)) / ((1 - R)**2 * exp(-a * l2))

= exp(-a * l1)) / exp(-a * l2)) = T_int(l1) / T_int(l2)

and considering the relationship between internal transmittances:

T_int(l1) = T_int(l2)**(l1/l2)

we can compute:

T_ext(l1) / T_ext(l2) = T_int(l2)**((l1 - l2) / l2)

thus:

T_int(l2) = (T_ext(l1) / T_ext(l2))**(l2 / (l1 - l2))