PDLC vs. PNLC — smart glass technologies compared

The Evolution of Transparency: Dynamic Glazing Beyond Mechanical Blinds

In contemporary architecture, glass is no longer just a separating element but an active component of the building envelope. The static nature of conventional glazing has long reached its limits when discretion and light-flooded spaces were required simultaneously. With the emergence of Polymer Dispersed Liquid Crystal (PDLC) and its technological further development, Polymer Network Liquid Crystal (PNLC), the paradigm has shifted. Today, we no longer speak of glass as a building material, but as a visual infrastructure that adapts to user needs in milliseconds. This is not just about the optical effect, but about measurable parameters such as thermal load, UV protection, and the reduction of operating costs by dispensing with mechanical shading systems.

The Technological Basis: Liquid Crystals and Electric Fields

Both technologies are based on the manipulation of liquid crystals embedded in a polymer matrix between two conductive layers (usually ITO – Indium Tin Oxide). However, the decisive difference lies in the arrangement of these crystals in the de-energised state and the resulting optical characteristics.

In PDLC (Polymer Dispersed Liquid Crystal), the crystals are disordered without electrical voltage. The incident light is scattered in all directions, leading to an opaque, milky-white appearance. Only when an AC voltage (typically between 48V and 110V AC) is applied do the crystals align parallel to the electric field. Light can pass through the layer unhindered – the glass becomes transparent.

PNLC (Polymer Network Liquid Crystal) reverses this principle. Due to a specific cross-linking of the polymers, the crystals are already aligned in the idle state. The glass is transparent without any energy being expended. When a voltage is applied, the order breaks down, the crystals scatter the light, and the glass becomes opaque. This "reverse mode" is technologically more demanding to manufacture but offers significant advantages in specific use cases regarding service life and fail-safety.

PDLC vs. PNLC: A Technical Comparison

In practice, nuances often decide the suitability for a project. Here are the physical and operational key figures that planners must consult.

Optical Quality: The Haze Factor

A critical value for the acceptance of smart glass is the so-called "haze". This describes the proportion of light that, when passing through the clear glass, is scattered by more than 2.5 degrees from the axis of incidence. A high haze value in the transparent state leads to a slightly cloudy shimmer, which is particularly noticeable at shallow viewing angles. Modern high-end films from manufacturers such as Gauzy or Polytronix achieve haze values of significantly below 4% in the PDLC sector. Due to the system design, PNLC systems often exhibit an even higher initial clarity, as the polymer structure creates fewer interferences with the light path in the idle state.

The Energy Question: When PNLC Wins Economically

The choice of technology has a direct influence on the building's energy consumption. Since PDLC requires energy to be transparent, it is the ideal choice for rooms that are intended to remain private (opaque) most of the time – such as treatment rooms in clinics or conference rooms that only allow a view when required.

In modern office landscapes or on building façades, however, an opposite requirement often prevails: the glass should be transparent for the majority of the day to utilise daylight (daylight harvesting) and only switch to opaque in the evening hours or for specific meetings. Here, PNLC offers a decisive advantage: it consumes zero grams of electricity in the transparent state (approx. 90% of operating time). This not only reduces operating costs but also protects the transformers and control units, which extends the overall service life of the hardware.

Installation and Control: The Role of Inverters and Control Protocols

Smart glass is not a passive building element, but an electrical component. Integration requires precise engineering at the interface between glass construction and electrical engineering. At Lumexo, we usually work with systems based on 48V AC, as these offer higher safety during installation and lower insulation requirements compared to 110V systems.

Control is handled via specialised inverters that convert the building's DC signal into the AC voltage necessary for the liquid crystals. Integration into common protocols is important here:

1. DALI-2 / KNX: For automated control via the building management system (BMS).
2. 0-10V Dimming: Enables not only "on/off" but also intermediate stages of transparency (deep dimming), for example, to reduce glare without completely darkening the room.
3. RS485 / Modbus: For complex networking in smart buildings.

Practical Example: Financial Service Provider Headquarter (Vienna)

Setting: A newly built headquarter with a central atrium and 12 adjacent high-level meeting rooms.

Challenge: The architecture demanded maximum transparency so as not to disturb the spatial feeling of the atrium. At the same time, the glass fronts had to become opaque within a second for discreet negotiations. Since the rooms function as open work zones 80% of the day, energy consumption was a central criterion.

Solution: Use of PNLC laminated glass (Laminated Safety Glass) in a 12.76 mm configuration (66.2).

• Hardware: PNLC inlays with controlled polymer structure.
• Control: Integration into the existing Crestron system via 0-10V interfaces.
• Result: In the de-energised state, the rooms are crystal clear (haze < 3%). When activating "privacy mode" via the touch panel at the end of the table, the glass switches to opaque in 80 ms. The annual energy savings compared to a PDLC solution amount to approx. 1,200 kWh for this area, as transparency is maintained without power supply.

What We See in Practice

Based on numerous installations in the DACH region, clear trends and pitfalls can be identified:

1. Edge Sealing is Crucial: Liquid crystal films are sensitive to moisture. Inadequate sealing of the glass edges leads to delamination or bluish discolouration at the edges in the long term. We recommend specialised silicones that are neutral-curing.
2. The Importance of Toughened Safety Glass (TSG): Smart glass is almost always produced as laminated safety glass (LSG). Thermal stress caused by light absorption (especially in outdoor applications) requires the use of TSG to avoid stress cracks.
3. UV Protection: High-quality inlays block up to 99% of UV radiation. This is an often-underestimated benefit that drastically reduces the fading of interiors and floor coverings in sun-exposed rooms.
4. The "Fail-Safe" Discussion: In escape routes, glass must be transparent in the event of a power failure. Here, PNLC is the only logical choice as it remains transparent without voltage. PDLC would visually block the escape route during a blackout.
5. Bus Topology vs. Star Cabling: For large areas, the planning of cable routes is decisive. We often see that cross-sections for long runs are underestimated, leading to voltage drops and uneven switching behaviour.

Standards and Guidelines

Central standards must be considered during planning:

• EN ISO 12543: Glass in building – Laminated glass and laminated safety glass.
• DIN EN 12150: Thermally toughened soda lime silicate safety glass.
• Low Voltage Directive (2014/35/EU): For the electrical components of the control system.
• BFSG 2025 (Barrierefreiheitsstärkungsgesetz): Relevant for kiosk systems with integrated smart glass.

Recommendation from Lumexo

The choice of the right technology should always start from the "default position" of the glass:

• Choose PDLC if the standard state of your room requires privacy (e.g. changing rooms, treatment rooms, toilet partitions). It is the more cost-effective and most widely used solution.
• Choose PNLC if the glass is to be transparent most of the time (e.g. shopfronts, office partitions, façades). The higher initial investment pays off through lower operating costs and the fail-safe property.
• Look for Certified Inverters: Use only control units designed for continuous operation with protection circuits against voltage peaks. An imprecise sine wave massively shortens the service life of the liquid crystals.
• Early Planning of Electrical Trades: Smart glass is not a product you "install and forget". Coordination between drywall construction (cable routes), electrical (subdivision of circuits), and glass construction must be completed by design stage 3.