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Light transmission

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Light Transmission (LT): definition

Light transmission (LT) is an indicator that measures the proportion of light that passes through a glazing unit. Expressed as a percentage, the higher this factor is, the more natural light will enter the room.


The lower the light transmission, the less transparent the glazing.

Light characteristics

When glazing is exposed to light, it transmits some (LT), reflects some (RL) and absorbs the rest (AL).


LT + RL + AL = 100%

light transmission diagram

The light transmission of clear glazing



Light transmission

Single glazing

Double glazing

Double glazing

with low-emissivity layer

Triple glazing

Triple glazing
with low emissivity layer


4 / 20A / 4 - 28mm

4 / 20A / 4 FE - 28mm

4 / 20A / 4 / 20A / 4 - 52mm

4 / 20A / 4 / 20A / 4 FE - 52mm





Between 57% and 65%

depending on the number of low-emissivity layers

The light transmission of clear glazing is determined by the number of glasses and their thickness. On the other hand, the space between the panes (usually made up of argon) has no influence on light transmission (LT).

Light transmission and solar factor

Light transmittance (LT) and solar factor (Sg) are closely related . When we are looking for high-performance glazing, particularly to reduce summer overheating, we look for a low solar factor. It is then necessary to pay attention to light transmission, which is sometimes very low for solar protection devices.

Light transmission of solar control glazing

To function, solar control glazing filters part of the UV radiation, part of the bottom and top of the visible spectrum as well as infrared radiation.

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©SNFPSA - 2017

Solar control glazing with a low solar factor necessarily implies low light transmission, and therefore darker glazing.


IMMOBLADE offers solar control glazing solutions - for commercial buildings - that optimize the solar factor all year round, while maintaining a higher light transmission (around 60%) than standard solar control glazing.

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