Questions covered in this guide
Describe the light you want
Record which room feels dim, at what time, and which activities need better light. Note nearby buildings, trees, shades and deep exterior overhangs. Take comparable photographs for the discussion with your seller, but do not treat a phone image as a light measurement. Start with a clear room concern rather than automatically choosing the highest number.
Find the rating for the order
NFRC visible transmittance describes daylight admitted through a product. Higher values indicate more visible light transmission. Ask for the value applying to the actual frame and glass configuration being quoted. Have the seller explain any difference between a sample’s label and your proposed product. Keep the solar-heat rating in a separate column; a daylight number alone does not describe all the effects of a glass choice.
Compare the full daylight arrangement
Make rows for glass package, visible transmittance, frame proportions, grille pattern and planned shades. Ask whether a change that appears small in the catalog alters the amount or distribution of visible glass in your opening. Review a sample from the intended side and discuss any tint or reflection you find distracting. Compare two otherwise matching proposals so a different frame or shade does not get mistaken for a glass-only difference. Ask a designer for a more detailed daylight assessment if the room problem remains unresolved.
Keep the decision and budget together
Save the chosen configuration and supporting rating with the opening list. Request the installed price difference and avoid translating the daylight rating into a lighting-bill saving without a separate analysis. Use the window calculator to organize the quoted replacement amounts. It cannot predict the final brightness of a room or select an appropriate glass package from a single rating.
Sources and supported claims
NFRC visible transmittance describes daylight admitted through a product.
Source ↗ · national · Checked 2026-10-12
Higher values indicate more visible light transmission.
Source ↗ · national · Checked 2026-10-12
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