Understanding Low-Emissivity Glass: A Complete Guide

Glass has become one of the most versatile materials in modern building, largely thanks to its constantly improving solar and thermal performance capabilities.

While glass might appear to be just a barrier to keep rain and insects out, it has evolved immensely over the years. Most of us look through windows without giving them a second thought, but as our homes demand more energy-efficient materials, standard glass simply doesn't cut it anymore.

To improve internal home performance, engineers have developed passive and solar control low-emissivity (low-e) coatings. However, before diving into these innovations, it's important to understand how different light wavelengths impact our homes.

“Low-E is not only to stop heat from direct sunlight, but to increase the insulation properties of glass, exclusive of direct sunlight.”

What are the three light wavelengths?

When discussing energy-efficient windows and their impact on your home, understanding the different types of light that pass through them is crucial.

Sunlight contains a spectrum of light wavelengths, each affecting your home differently. It's worth noting that Low-E glass dramatically affects infrared light (heat), and newer generations of Low-E technology don't impact visible light, meaning they won't tint or color your glass. Let's explore the three main types.

Ultraviolet Light: 310-380 nanometers

• Invisible to the naked eye but significantly impacts your home and belongings

• Breaks down bonds in dyes and materials over time, causing fading

• Can cause skin aging even when you're indoors near windows

• Standard window glass blocks some UV light, but specialised treatments and coatings can block up to 99% of harmful UV rays, protecting both your home's interior and your family's health

Visible Light: 380-780 nanometers

• The light we actually see that brightens our homes

• Essential for mood, productivity, and overall wellbeing

• Modern Low-E coatings are designed to maximise visible light transmission while controlling other wavelengths

Infrared Light: 780+ nanometres

• The heat you feel from sunlight

• Warms your home naturally, you can feel this when standing near a sunny window

• Can lead to overheating and increased cooling costs during summer months

Understanding these different light wavelengths helps explain why modern energy-efficient windows are engineered with such complexity and precision.

What is low-emissivity glass?

Think of low-E glass as a smart filter for your windows. While regular glass lets all types of light and heat pass through freely, Low-E glass acts like a selective bouncer, welcoming visible light for brightness while turning away excess heat that drives up your energy bills. This happens through an ultra-thin coating applied to the glass surface. This coating is incredibly thin — imagine something 500 times finer than a strand of human hair! But it transforms how your windows perform.

Every material has what scientists call an ‘emissivity rating’. Emissivity measures a material's ability to emit thermal radiation, with values ranging from 0 (perfect reflector) to 1 (perfect emitter). Picture a shiny mirror versus a dark brick wall on a hot day. The mirror stays relatively cool because it reflects heat away (low emissivity), while the brick absorbs and radiates heat (high emissivity).

Low-E glass works on this same principle. The special coating creates a surface that reflects infrared heat energy back to where it came from, rather than letting it pass through your window. In summer, this means outdoor heat bounces back outside. In winter, it means your indoor heating stays inside where you want it.

Modern Low-E glass can be designed for your specific location. Living in Darwin's tropical heat? You'll want a coating that blocks maximum solar heat gain. Residing in Hobart's cooler climate? A coating that allows some beneficial winter sun while still providing insulation makes more sense. This customisation means your windows work with your local weather patterns, not against them.

How many types of low-emissivity glass are there?

There are two main technologies in Low-E glass manufacturing: Hard Coat and Soft Coat.

Traditional technology: Hard Coat

• Designed for single glazing applications

• Mixed directly into the glass during manufacturing

• While performance does improve, the metallic content can oxidize in the atmosphere, creating a cloudy appearance over time

• Dramatically affects visible light transmission, often creating noticeable tinting

Modern technology: Soft Coat

• Exclusive to double glazing systems, protected within the sealed unit

• Not prone to oxidation since it's sealed between glass panes

• Remains extremely clear throughout its lifespan

• Doesn't affect visual light transmittance, maintaining crystal-clear views

There is a wide variety of Low-E glass types available, and while they all excel at retaining heat and cool air in your home, they can be manufactured to block specific proportions of direct sunlight's heat. The key is matching the right type to your climate:

• Cold climates: Use High Solar Heat Gain Low-E for winter warmth

• Hot climates: Use Low Solar Heat Gain Low-E for summer cooling

How can you measure low-emissivity glass performance?

Understanding window performance requires familiarity with several key measurements:

• U-Value: The rating given to a window is based on how much heat loss it allows. Lower U-values indicate better insulation performance.

• Solar Heat Gain Coefficient (SHGC): The fraction of incident solar radiation admitted through a window, including both directly transmitted light and heat absorbed and re-radiated inward. Lower SHGC values mean less solar heat transmission.

• Visible Light Transmission (VLT): This percentage indicates how much visible light passes through the window. Higher numbers mean brighter interiors with reduced need for artificial lighting during the day.

The LightBridge™ glass we use in our Miglas products measures well on all of these metrics.

Protect, reduce, and maintain

When selecting windows for your home, consider how they handle all three types of light, not just their insulation properties. This comprehensive approach makes sure the best combination of protection and energy efficiency happens.

High-performing Low-E windows offer a triple benefit: they protect your belongings from UV damage, reduce energy costs through improved thermal performance, and maintain year-round comfort in your living spaces.

Ready to upgrade your home's windows with advanced Low-E technology? 

Contact our team at Miglas today to discover how our premium low-emissivity glass solutions can transform your home's energy efficiency and comfort.