Antireflective stack for low luminance conditions
Ophthalmic lens comprising an anti-reflective stack designed for scotopic or mesopic conditions, wherein the anti-reflective stack design method uses the scotopic luminosity function CIE 1951 (defined by the Commission Internationale de I'Eclairage).
1. An ophthalmic lens comprising an anti-reflective stack designed for scotopic or mesopic conditions, wherein:
the anti-reflective stack design method uses the spectral luminous efficiency function V′(λ) as defined in CIE 1951 and an average spectral luminous efficiency function V α,β (λ)=αV(λ)+βV′(λ), with β>0, V(λ) is in CIE 1931 and V′(λ) is in CIE 1951; and
the anti-reflective stack has a mean light reflection R V α,β value that is calculated according to:
R
V
α
,
β
=
∫
380
780
R
(
λ
)
·
V
α
,
β
(
λ
)
·
Ilum
(
λ
)
·
d
λ
∫
380
780
V
α
,
β
(
λ
)
·
Ilum
(
λ
)
·
d
λ
wherein R(λ) is the light reflection spectrum of the anti-reflective stack and Ilum(λ) is a reference illuminant.
2. The ophthalmic lens according to claim 1 comprising a transparent substrate with a front main face and with a rear main face, at least one of the main faces being coated with a multilayered anti-reflective stack comprising at least one layer having a refractive index higher than or equal to 1.55 and at least one layer having a refractive index lower than 1.55, such that:
the mean light reflection factor in the visible region for photopic vision R V with D 65 illuminant is lower than or equal to 0.5%, for at least an angle of incidence lower than 35°; and
the mean light reflection factor in the visible region for scotopic or mesopic vision R V α,β with D 65 illuminant is lower than the mean light reflection factor in the visible region for photopic vision R V for at least an angle of incidence lower than 35° and a ratio α/β≤10.
3. The ophthalmic lens according to claim 2 , wherein the multilayered anti-reflective coating comprises a number of layers higher than or equal to 3 and lower than or equal to 10, preferably higher than or equal to 4 and lower than or equal to 6.
4. The ophthalmic lens according to claim 1 , wherein the hue of the light reflected by the anti-reflective coating is in the range from 0° to 150° for at least an angle of incidence lower than 35°.
5. The ophthalmic lens according to claim 1 , wherein mean reflection factor Rm of anti-reflective coating is lower than 1% for at least an angle of incidence lower than 35°.
6. The ophthalmic lens according to claim 1 , wherein the anti-reflective coating comprises, in the direction moving away from the substrate, a layer having a refractive index higher than or equal to 1.55 with a thickness of from 10 to 25 nm, a layer having a refractive index lower than 1.55 with a thickness of from 20 to 35 nm, a layer having a refractive index higher than 1.55 with a thickness of from 60 to 110 nm, optionally an electrically conductive layer with a thickness of from 3 to 10 nm, and a layer having a refractive index lower than 1.55, with a thickness of from 70 to 95 nm.
7. The ophthalmic lens according to claim 1 comprising a front face coated with said multilayered anti-reflective stack and an indication of a visual rating associated with the ophthalmic lens, wherein the visual rating including a ratio based on values α and β defining the average spectral luminous efficiency function V α,β (λ) used for designing the anti-reflective stack.
8. A method of designing an anti-reflective stack comprising:
(a) identifying a luminance in the scotopic vision regime;
(b) calculating the weighted mean light reflection in scotopic conditions R V ′ of an anti-reflective stack having a light reflection spectrum R(λ) according to:
R
V
′
=
∫
380
780
R
(
λ
)
·
V
0
,
1
(
λ
)
·
Ilum
(
λ
)
·
d
λ
∫
380
780
V
0
,
1
(
λ
)
·
Ilum
(
λ
)
·
d
λ
(c) designing an anti-reflective stack by selecting materials to achieve the light reflection spectrum R(λ) yielding the calculated R V ′ value,
wherein V 0,1 (λ)=V′(λ) is in CIE 1951 and Ilum(λ) is a reference illuminant.
9. The method of claim 8 , wherein R V ′ is less than or equal to 1%, preferably less than or equal to 0.5%.
10. The method of claim 8 , further defined as manufacturing an ophthalmic lens having an anti-reflective stack, further comprising:
(d) providing an optical article having two main faces; and
(e) forming the anti-reflective stack on at least one main face of the ophthalmic lens.
11. A method of designing an anti-reflective stack comprising:
(a) identifying a range of luminance in the scotopic and/or mesopic vision regime;
(b) calculating the average spectral luminous efficiency function V α,β (λ) of the range of luminance according to:
V α,β (λ)=α V (λ)+β V ′(λ)
wherein α and β are selected according to the luminance conditions, β>0, V(λ) is in CIE 1931 and V′(λ) is in CIE 1951;
(c) designing an anti-reflective stack by use of V α,β (λ) function.
12. The method of designing an anti-reflective stack according to claim 11 in which step (c) comprises the following steps:
(c1) calculating the weighted mean light reflection R V α,β of an anti-reflective stack having a light reflection spectrum R(λ) according to:
R
V
α
,
β
=
∫
380
780
R
(
λ
)
·
V
α
,
β
(
λ
)
·
Ilum
(
λ
)
·
d
λ
∫
380
780
V
α
,
β
(
λ
)
·
Ilum
(
λ
)
·
d
λ
(c2) designing an anti-reflective stack by selecting materials to achieve the light reflection spectrum R(λ) yielding the calculated R V α,β value,
wherein Ilum(λ) is a reference illuminant.
13. The method of claim 11 , wherein R V α,β is less than or equal to 1%, preferably less than or equal to 0.5%.
14. The method of claim 11 , further defined as manufacturing an ophthalmic lens having an anti-reflective stack, further comprising:
(d) providing an optical article having two main faces; and
(e) forming the anti-reflective stack on at least one main face of the ophthalmic lens.
15. The method of claim 14 further comprising providing to a customer of said ophthalmic lens a rating of the ophthalmic lens with respect to luminance conditions, the rating being based on a ratio α/β, which quantifies the anti-reflective efficiency of the ophthalmic lens in scotopic or mesopic conditions.