Light protection
Function
The two most important functions of light-protective glass:
- Reflecting or absorbing a portion of the light and energy content of sunlight.
- Preventing visibility from outside.
The latter function is more effectively fulfilled when the difference in light intensity between the exterior and the interior is greater. If the interior light intensity is higher than the exterior, this type of glass cannot prevent visibility from outside.
Light-protective products are especially significant in buildings with large glass surfaces equipped with air conditioning, as they prevent unwanted heating of the interior spaces. It should be noted that these glasses work similarly in winter, meaning that we lose the "free" heating provided by sunlight. Considering that cooling by 1 Celsius degree requires four times more energy than heating by 1 Celsius degree, this is an important factor.
In general, using light-protective glass reduces both the transmission of natural sunlight and solar energy.
Don't be afraid of combined solutions! Different types of glass can be used on a building according to the orientation of the facades without causing architectural disruption. In many cases, people inside may not even notice that the glass on different facades is of different types and has different parameters.
Based on the above, it can be said that many factors need to be considered to select the most optimal glass structures for each project. For any questions, feel free to contact our sales representatives!
Types of Light-Protective Glass
- Reflective glass
- Colored glass (non-coated)
- Multifunctional glass
- Reflective solar-protective glass can also be made by coating colored base glass.
Main Parameters
LT Value (Light Transmission) - Visible Light Transmission Capability
The light transmission value of the glass shows what percentage of light is allowed to pass into the interior. For standard "4-16arg-4low-e" insulating glass, it is 82%, and for standard triple-layer low-e coated insulating glass, it is only 74%. The more natural light we can let in, the less artificial lighting and energy we need to use.
LR Value (Light Reflection) - Visible Light Reflection Capability towards the Outdoors
The light reflection (light reflexion) value of the glass shows what percentage of incoming light from the outside is reflected by the glass. The higher this value, the more sunlight is reflected by the surface (the more reflective it is). For example, a strong reflective glass (LR=36%) can be three times as reflective as standard "4-16arg-4low-e" insulating glass (LR=12%).
SF Value (Solar Factor) - Total Solar Energy Transmission Capability
The total solar energy transmission value shows what percentage of the solar energy hitting the facade is allowed through by the glass structure. The lower the SF value, the less air conditioning is needed in the summer, reducing cooling costs and electricity bills. The solar energy transmission capability of standard "4-16arg-4low-e" insulating glass is 64%, while for triple-layer low-e coated glass, it is 53%.
S Value (Selectivity) - Ratio of Visible Light Transmission to Total Solar Energy Transmission (S = LT / SF)
The higher the value, the more advanced the glass structure.
Today, every major base glass manufacturer has glass types with selectivity around 2.2.
For standard "4-16arg-4low-e" insulating glass, the value is 1.28, and for standard triple-layer low-e coated insulating glass, it is 1.41.
Modern solar control glasses have a selectivity of over 1.7.
EA Value (Energy Absorption) - Energy Absorption
A portion of the solar energy hitting the glass structure is always absorbed by the glass. For standard "4-16arg-4low-e" insulating glass, the energy absorption is 13.9%, and for standard triple-layer low-e coated insulating glass, it is 20.5%.
There is a risk of thermal breakage for multi-layer glasses if:
- The EA value of one glass pane reaches 50%,
- or the total EA value of the insulating glass reaches 60%.
Thermal breakage can be prevented by tempering or heat-strenghtening. Not all base glass can be tempered or heat strenghtened, and tempering itself incurs additional costs, so please consult our sales representatives for the evaluation of specific cases!