How it behaves
What happens during a power cut?
The glass turns opaque. PDLC is clear only while powered, so losing power means losing transparency — it fails to private, never to exposed. For most rooms that is the safe direction, but not for all of them.
Fail-safe direction: power off means opaque. Your privacy is never compromised by a power failure — but natural light and visibility through the pane are.
Why it works this way
In its resting state the liquid crystals inside PDLC film are randomly scattered, so they diffuse light and the pane looks frosted. Applying voltage aligns them, letting light pass in a straight line — that is the clear state.
Opacity is therefore the film's natural condition. Transparency is the state that requires energy. This is the opposite of what most people assume, and it is worth confirming with anyone specifying the glass.
The practical consequence is that a power cut is a privacy event in your favour, and a daylight event against you. Whether that trade-off is acceptable depends entirely on the room.
What it means room by room
| Space | Effect of a power cut | Recommendation |
|---|---|---|
| Conference room | Goes private; room gets darker | Usually fine — no action needed |
| Bathroom / shower | Goes private | Ideal — this is the desired fail state |
| Hospital ICU bay | Goes private; staff lose visual line of sight | Put on backup power circuit |
| Internal partition | Room loses borrowed light | Consider backup if the space is windowless |
| External window | Goes opaque; daylight lost | Backup power or pair with openable glazing |
| Skylight | Goes opaque; overhead daylight lost | Backup power strongly advised |
| Retail display | Goes opaque; merchandise hidden | Backup power advised |
Designing around it
- Put critical panels — ICU bays, skylights, display windows — on UPS or generator circuits
- The load is tiny: roughly 5W per m², so a modest UPS covers a large area
- Never make PDLC the only light source strategy for a windowless room
- In healthcare, confirm the fail state against your clinical observation protocol
- Tell the facilities team it is expected behaviour, not a fault
- For escape routes, check the fail-opaque state against fire and egress requirements
Common questions
Can PDLC be made to fail clear instead of opaque?
Not with standard PDLC — the physics runs the other way. Reverse-mode film exists (clear when off, opaque when on) but it is more expensive, less widely available and generally has poorer optical clarity. For most projects a UPS is the cheaper and better answer.
How much backup power does it need?
Very little. At roughly 5W per square metre, 20 m² of glass draws about 100W in the clear state — comparable to a couple of light bulbs. A small UPS will hold a substantial installation.
Does a power cut damage the film?
No. Losing power is the film's resting state and causes no harm at all. It returns to clear the instant power is restored.
What about voltage fluctuations?
The driver regulates supply, so normal fluctuation is handled. Severe surges can damage the controller — in areas with unstable supply we recommend surge protection on the circuit.
Keep reading
Related guides
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