Glossary of Skylight Terms E – L

Electric Venting Skylight

A skylight equipped with an electric motor, allowing it to be opened and closed remotely. This offers added convenience, making it easy to ventilate a room without any physical effort.

Energy Star Rating

A label indicating the energy efficiency of a skylight. It is set based on criteria developed by the U.S. Environmental Protection Agency (EPA).

Choosing products with this label helps reduce heating and cooling costs and contributes to sustainable development.

ENERGY STAR®

A U.S. government program run in collaboration with the Environmental Protection Agency (EPA) and the Department of Energy (DOE). VELUX has joined the initiative to improve the energy efficiency of its products by 40%.

Fixed Skylight

A stationary skylight that cannot be opened and is not intended for ventilation. Its primary function is to let natural light in, creating a bright and spacious atmosphere in a room, without the option for air circulation.

Flashing

A corrosion-resistant material, often made of aluminum, used to protect a structure from water penetration. Its main function is to control, redirect, or prevent moisture from entering the building’s structure.

Also known as: roof flashing

Frame

This is the structural foundation designed to provide shape and support to the window system. It surrounds and holds the glass in place, ensuring its stability, while also protecting the window from external elements such as wind, rain, or temperature fluctuations. The frame is a critical component of the window, as its strength and quality directly affect the durability and reliability of the entire structure.

For the manufacture of frames in roof windows and skylights, Velux exclusively uses northern pine, grown in young forests.

Gasket

This is a sealing element designed to prevent leaks between the frame and the glass. It ensures a reliable seal, preventing the penetration of water, air, and dust. This component plays a key role in improving thermal and sound insulation and also contributes to the window’s longevity by protecting it from the impact of external factors.

Glazing

This is the transparent material, typically glass or plastic, installed in windows, doors, and skylights. It allows natural light to enter the room while providing reliable protection from weather conditions and other external influences.

VELUX offers two types of glazing units: Comfort Glass and ComfortPlus Glass. Comfort Glass consists of two layers of tempered glass, bonded at the edges with a stainless-steel spacer and two durable seals. ComfortPlus Glass differs in that its outer side consists of tempered glass layers connected to a multi-layered inner glass. Both types of glazing units are filled with argon and have a double low-emissivity coating, developed using VELUX’s exclusive technology.

Known as insulated glazing.

Haze Factor

This is an indicator that defines the percentage of light scattered through the glass surface. The higher this value, the more light loses its clarity, becoming soft and diffused. For example, a 100% haze factor means that all light passing through is scattered. (According to regulations, the haze factor for skylights should be at least 90%.)

Heat-Strengthened Glass Skylights

This is glass that undergoes a special thermal treatment, during which it is heated in controlled conditions to create internal stress. This process makes the glass twice as strong as regular glass, providing high resistance to mechanical damage and temperature fluctuations.

Also known as: tempered glass, safety glass.

Impact Glass

This is impact-resistant glass, specially designed to protect against the penetration of flying objects. It meets the stringent requirements for protection against flying debris set by the IBC (International Building Code for commercial buildings), IRC (International Residential Code), and the 2001 Florida Building Code, excluding protocols from Miami-Dade County. This glass serves as a reliable barrier, ensuring the safety of buildings during severe storms and other adverse weather conditions.

Insulated Glazing Unit (IGU)

This is a double-glazed unit consisting of several glass panels separated by an air or gas layer. This construction effectively provides sound and thermal insulation, enhancing energy efficiency in a building and helping to maintain a comfortable temperature.

Joist

A joist is a load-bearing beam installed parallel to other beams and serves to support ceiling structures. They distribute the load and help maintain the strength and stability of the structure.

Laminated Glass

This is a structure made up of multiple layers of glass (two or more) bonded together with a strong plastic film, most commonly polyvinyl butyral (PVB). It holds the glass together even when damaged, preventing shards from scattering. As a result, laminated glass offers increased safety and durability.

Also known as: laminated tempered glass, laminated glass windows, laminated tempered glass.

Light shaft

This is a special structure between a flat ceiling with attic space and the roofline, designed to direct light and provide a view from the roof into the interior spaces.

The main purpose of a light shaft is to fill the room with natural light, creating a sense of greater volume and reducing the need for artificial lighting during the day.

LoE3

This is a special metallic coating applied to glass to improve its thermal insulation properties. It helps reduce heat loss during the winter and minimizes heat buildup in the summer by reflecting infrared radiation. Additionally, it blocks harmful ultraviolet rays, protecting furniture and interiors from fading.

Also known as: low e glass, low e insulation, low e window coating, low e glass coatings, low e windows, low emissivity coating, e glass, lo e windows.

Lumen (lm)

A unit used to measure luminous flux in the SI system. It indicates how much visible light is emitted by a source, distributed in space through a solid angle (steradian). One lumen corresponds to the amount of light emitted by a source with a brightness of one candela (cd) that evenly distributes light in all directions.

Lumen measures the amount of light perceived by the human eye, as opposed to radiant flux, which measures the total power of all electromagnetic waves emitted by a source. Unlike radiant flux, lumen accounts for the fact that the eye perceives different wavelengths differently, reflecting only the light we can see.

Thus, lumen allows for an accurate measurement of the “volume” of light available for human perception and helps better understand how bright or dim a light source will appear in real life.

Lux (lx)

A unit of measurement used to evaluate the level of illumination in the SI system. It shows how much light is falling on a specific area of a surface.

1 Lux equals 1 lumen spread over 1 square meter.