Smart glass technologies compared
Six technologies, and only two of them do the same job
"Smart glass" is not a product category. It is a label over two different jobs that happen to be solved by glass that changes: hiding something, and shading something. A boardroom needs the first. A west-facing atrium needs the second. Specify a technology that does the other one and no amount of commissioning will fix it.
So the first question is not which technology. It is which of those two problems is on the drawing — and then, whether the glass should be clear or private when nothing is switched on.
Which job each one does
| Technology | What it does | Gives privacy | Controls glare and solar gain |
|---|---|---|---|
| PDLC — normal mode | Frosts and clears | Yes | Barely — it stays bright when frosted |
| PNLC — reverse mode | Frosts and clears, the other way round | Yes | Barely |
| DLC — dynamic liquid crystal | Dims and clears, and hazes as it darkens | Yes | Yes |
| SPD — suspended particle | Dims to a dark tint | No | Yes |
| Electrochromic | Tints, slowly | No | Yes |
| Thermochromic | Tints with temperature, passively | No | Partly — it is not controlled |
| Cholesteric liquid crystal | Switches and holds its state | Yes | Depends on the build |
The row that surprises people is the second column of PDLC. A frosted panel is not a dark one — it transmits 83 to 88 per cent of the light falling on it and scatters it. That is why a frosted partition still lights the room behind it, and why frosting a west elevation does very little about the heat.
How they behave, side by side
PriWatt figures are the published ones for our own products. The rest describe how the technology behaves rather than any particular manufacturer’s product — ranges and switching times vary with the build-up, the size and the vendor, so they are given as orders of magnitude and should be confirmed against a datasheet before anything is specified.
| Switching | State with no power | Power to hold a state | Controlled by | |
|---|---|---|---|---|
| PDLC (PriWatt) | < 10 ms to clear · < 200 ms to private | Private | < 0.5 W/sq ft, to stay clear | Switch, remote, building system |
| PNLC (PriWatt) | < 150 ms to clear · < 5 ms to private | Clear | < 0.5 W/sq ft, to stay private | Switch, remote, building system |
| DLC (PriWatt) | < 150 ms to clear · < 5 ms to dark | Dark | < 0.5 W/sq ft, to stay clear | Switch, remote, building system |
| SPD | Seconds | Dark | Continuous, to stay clear | Switch, and it dims through the range |
| Electrochromic | One to five minutes | Holds where it was | Almost none | Controller, usually with tint levels |
| Thermochromic | As the glass warms | Whatever the temperature makes it | None | Nothing — it is passive |
| Cholesteric LC | Fast | Holds where it was | Almost none | Controller |
Where each one wins
Privacy, instantly — liquid crystal
Nothing else conceals. A partition, a consulting room, an observation wall or a shower needs a surface you cannot see through, and only the liquid-crystal products produce one. They also switch in milliseconds rather than minutes, which is the difference between a room that closes as someone sits down and one that closes after the meeting starts.
A facade held tinted all day — electrochromic
This is the comparison that goes against us. Electrochromic glazing holds its tint at almost no power, so a large elevation that stays tinted through a working day spends very little to do it. A liquid-crystal panel draws power for every hour it is held in the switched state. On that specific job, the slow technology is the efficient one.
Deep dimming with no privacy — SPD
SPD goes properly dark and dims smoothly through its range, which suits a rooflight or a vehicle. It does not frost, so it is never the answer to a privacy brief — and like the liquid-crystal products, it is clear only while it is powered.
No wiring at all — thermochromic
Passive glazing tints as it heats and needs no power, no control and no commissioning. The trade is total: nobody can switch it, so it responds to the weather rather than to the room.
Under half a watt per square foot — and it matters which state that is
PriWatt panels draw under 0.5 W per square foot, and only in the state that needs power. A 100 sq ft partition therefore draws under 50 W while switched — about 0.4 kWh if it is held that way for eight hours, and nothing at all for the rest of the day. That is arithmetic on the published figure, not a measured building.
Which state costs you that is the whole point of reverse mode. A glazed meeting room is transparent for most of the working week, so a reverse-mode panel spends most of the week drawing nothing. A shower enclosure is private most of the week, so normal mode does the same for the opposite reason. Specify the mode against how the room is actually used and the running cost mostly disappears.
Reverse mode in full
What changes when the glass is clear with no power — energy, the failure state, haze, and the rooms it is wrong for.
PDLC against PNLC
The two privacy modes compared line by line, with the numbers behind each row.
Every measured value
Optical, electrical and physical data for all six PriWatt products, in one table.
DLC is the exception in this table
The clean division between hiding and shading has one exception, and it is PriWatt’s own. DLC moves between a tinted transparent state and a deep dark one — 36% down to 4.5% light transmission at contrast 1:8, and 28% down to 1.5% at 1:15 — and its dark state carries 97% haze. It dims like a shading product and conceals like a privacy one, in milliseconds, on the same low-voltage control as the rest of the range.
It is the product for a rooflight, a west-facing storefront or an executive office where the brief is both. The overhead glazing page sets out where it is specified, and the DLC product page carries the full data.
Common questions
PDLC frosts: it scatters light so you cannot see through it, while still transmitting most of the light. SPD dims: it darkens towards a deep tint but you can still see through it. PDLC is a privacy technology and SPD is a shading one, and neither substitutes for the other. Both are clear only while powered — PriWatt also makes a reverse-mode product that is clear with no power at all.
For a facade that is held tinted through the day, electrochromic has a real advantage: it holds its state at almost no power, where a liquid-crystal panel draws power for every hour it is switched. For privacy it is not a candidate at all — it tints rather than frosts — and it takes one to five minutes to change, against milliseconds.
The liquid-crystal technologies, by a wide margin. PriWatt panels switch in milliseconds: under 10 ms to clear on PDLC, under 5 ms to private on PNLC. SPD takes seconds and electrochromic takes minutes, which is a property of how each one works rather than a quality difference.
The liquid-crystal ones — PDLC, PNLC, DLC in its dark state, and cholesteric LC. Tinting technologies such as SPD, electrochromic and thermochromic reduce light but you can still see through them, which is why they are specified for glare and solar gain rather than for concealment.
Only in the state that needs it. PriWatt panels draw under 0.5 W per square foot while switched and nothing at all in their unpowered state — which is private on PDLC and DLC, and clear on PNLC reverse. Choosing the mode against how the room is used is what keeps the running cost near zero.
Self-adhesive switchable film is applied to glazing that is already in the building, which is how offices, clinics and storefronts are converted without re-glazing. Laminated switchable glass is made for the opening instead. The choice between them is set out on the smart glass or smart film page.
Tell us the problem, not the technology
Whether the room needs to be hidden or shaded, which state it should hold with no power, and whether the glass is already in the building. That is enough to say which of the six is right — including when the answer is the cheaper one. Pompano Beach, Florida; (833) 333-8556.