Glass Glossary

Light to Solar Gain Ratio (LSG)


Last Updated: November 23, 2023

Light to Solar Gain Ratio (LSG) is a measure used to evaluate the energy efficiency of window glass. It compares the amount of visible light that a window allows to pass through (Visible Light Transmittance or VLT) to the amount of solar heat gain that the window allows to pass through (Solar Heat Gain Coefficient or SHGC). The ratio is expressed as a numerical value, typically ranging from 0 to 2.

Formula: LSG = VLT / SHGC

Interpretation:

A higher LSG indicates that a window allows more visible light to pass through while blocking more solar heat. Conversely, a lower LSG indicates that a window allows less visible light to pass through while allowing more solar heat to enter.

Key Factors Affecting LSG

Glass Coatings: LoĒ™ coatings and other reflective coatings can help increase the LSG by reducing the SHGC while maintaining high VLT.

Glass Thickness: The thickness of the glass can affect the LSG by influencing both VLT and SHGC.

Benefits of High LSG

Improved Energy Efficiency: Windows with high LSG provide better thermal insulation, reducing the need for artificial heating or cooling.

Enhanced Daylighting: High LSG windows allow more natural light to enter while minimizing solar heat gain, contributing to improved indoor lighting and reduced energy consumption.

Increased Comfort: By blocking solar heat while allowing visible light to pass through, high LSG windows create a more comfortable indoor environment.

Cost Savings: Windows with high LSG can reduce energy bills by minimizing the need for artificial heating or cooling.