Solar Protection Coating

All-dielectric solar-control coating on glass: UV and near-IR reflectors, with transmittances weighted by the ASTM G173 AM1.5 solar spectrum.

Model: Exact

n_H (high index)n_L (low index)n_glass

UV reflector: from (nm)UV reflector: to (nm)IR reflector: from (nm)IR reflector: to (nm)UV periods per stackIR periods per stack

Solar transmittance (AM1.5 G, 280–4000 nm)

—

Uncoated glass: 91.8 %

Solar energy reflected

—

Lossless layers and glass: nothing is absorbed

UV, 280–400 nm

T = —

Visible, 400–700 nm

T = —

Near IR, 700–4000 nm

T = —

Outer face: 1 × (H/2 L H/2)⁸ at λ₀ = 339.1 nm

Inner face: 2 × (L/2 H L/2)¹⁰ at λ₀ = 829.6, 1102.1 nm

Each band is covered by edge-filter stacks in series. The two faces add in intensity, T = T₁T₂/(1 − R₁R₂), and every transmittance is weighted by the ASTM G173 global-tilt spectrum: T = ∫T(λ)E(λ)dλ / ∫E(λ)dλ over the band. The chart's sunlight curve is that spectrum scaled to its peak.

Model and references

Exact. The equations are exact within the stated assumptions, or are a standard's tabulated values. The results are as good as the inputs. About the tiers

Edge-filter stacks in series on the two faces of lossless glass, normal incidence, faces added incoherently; weighted by the ASTM G173 global spectrum. Real glass absorbs in the IR.

Macleod H. A. (2010). Thin-Film Optical Filters, 4th ed., ch. 2 (incoherent reflection) and ch. 7 (edge filters). CRC Press. doi:10.1201/9781420073034
ASTM G173-03 (reapproved 2020). Standard Tables for Reference Solar Spectral Irradiances: Direct Normal and Hemispherical on 37° Tilted Surface. ASTM International. doi:10.1520/G0173-03R20

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