# Smart glass
**Smart glass**, also called switchable glass or dynamic glazing, is window glass whose light and heat transmittance can be changed on demand or in response to environmental conditions, allowing a window to alternate between clear and tinted or opaque states. The main technologies are electrochromic coatings, [polymer-dispersed liquid crystals](https://www.edgepedia.org/polymer-dispersed-liquid-crystal) (PDLC), suspended-particle devices (SPD), and passive thermochromic or photochromic materials. Electrochromic glazing, which switches with a small electric voltage, is described by the U.S. Department of Energy as the most technologically mature of the available dynamic glazing formulations[1](https://www.energy.gov/cmei/buildings/articles/better-windows-better-outcomes-how-electrochromics-improve-health).
| Key fact | Detail |
|---|---|
| How electrochromic glass works | A small amount of electricity drives protons or lithium ions into or out of coatings such as tungsten oxide, reversibly changing the glazing's solar and light transmittance[2](https://www.energy.gov/sites/default/files/2023-12/bto-electrochromic-window-report-121123.pdf) |
| Measured field performance | In a 2.5-year Berkeley Lab field test, electrochromic windows cut annual peak cooling load by 19–26% and lighting energy use by 48–67% versus an efficient low-e window with the same daylighting controls[3](https://windows.lbl.gov/publications/design-guide-early-market) |
| Current cost | Commercially available electrochromic technologies cost $50–$150 per square foot, a price premium of $35–$85 per square foot over static windows[2](https://www.energy.gov/sites/default/files/2023-12/bto-electrochromic-window-report-121123.pdf) |
| Solar heat gain range | Commercial EC glazing has solar heat gain coefficient (SHGC) values of 0.09–0.12 when tinted and 0.41–0.46 when clear[2](https://www.energy.gov/sites/default/files/2023-12/bto-electrochromic-window-report-121123.pdf) |
| National savings potential | Replacing existing U.S. windows with well-functioning dynamic windows would save about 2,400 TBtu across the residential and commercial sectors in 2030[4](https://www.energy.gov/cmei/buildings/articles/robust-large-scale-dynamic-windows-using-reversible-metal-0) |
## Technology families
**Electrochromic (EC) glazing** changes transmittance when a low voltage moves ions into or out of a thin coating, typically tungsten oxide, on the glass[2](https://www.energy.gov/sites/default/files/2023-12/bto-electrochromic-window-report-121123.pdf). The devices consist of two electrodes separated by an ion conductor, with transparent conductors forming the contacts[5](https://windows.lbl.gov/dynamic-glazings-advanced-coatings). Switching takes a few minutes for large-area windows[6](https://www.sciencedirect.com/science/article/pii/S0927024801001015), and tungsten oxide devices shift from deep blue to transparent while nickel oxide devices shift from transparent to brown, a color cast that affects light quality in the room[7](https://www.mdpi.com/2071-1050/13/17/9604).
**PDLC and SPD glass** PDLC glass primarily provides privacy, whereas SPD glass provides variable control of light, glare, and solar heat rather than serving privacy alone[15](https://www.smartglassinternational.com/news/spd-smartglass/). Suspended-particle devices work on a similar principle but suspend fine, strongly absorbing particles instead of liquid crystals[7](https://www.mdpi.com/2071-1050/13/17/9604).
**Passive chromic glazing** responds to natural stimuli without power. Thermochromic windows tint as temperature rises; the most studied material, vanadium dioxide (VO2), undergoes a reversible metal-to-insulator transition at a critical temperature of 68 °C, above which the material turns from infrared-transparent to infrared-translucent[9](https://www.frontiersin.org/journals/energy-research/articles/10.3389/fenrg.2021.800382/full). Photochromic glass darkens under sunlight. These systems cannot be manually controlled: a photochromic window may darken on a cold sunny day when solar heat gain is actually desirable, and a thermochromic window dims on warm days even when daylight is wanted[5](https://windows.lbl.gov/dynamic-glazings-advanced-coatings) • [7](https://www.mdpi.com/2071-1050/13/17/9604).
## Energy performance
The purpose of dynamic glazing is to modulate daylight, glare, and solar heat gain while preserving the view out, reducing energy use and peak electricity demand[3](https://windows.lbl.gov/publications/design-guide-early-market).
Simulation results cited by the Department of Energy show EC windows reducing peak cooling electricity demand by 5 to 7 W/m² across ten North American cities compared with static solar-control glazing, and cutting solar radiation gains by up to 88.9% versus code-minimum glazing[2](https://www.energy.gov/sites/default/files/2023-12/bto-electrochromic-window-report-121123.pdf). In a full-scale testbed, EC windows reduced peak cooling loads by an additional 25%–58% compared with spectrally selective low-e windows[2](https://www.energy.gov/sites/default/files/2023-12/bto-electrochromic-window-report-121123.pdf). Because tinted windows lower peak heat gain, buildings can sometimes install smaller HVAC systems, offsetting part of the glazing cost[2](https://www.energy.gov/sites/default/files/2023-12/bto-electrochromic-window-report-121123.pdf).
## Cost and market barriers
Cost is the main obstacle to widespread adoption. Commercially available EC technologies cost $50–$150 per square foot installed, with premiums of $35–$85 per square foot over static windows[2](https://www.energy.gov/sites/default/files/2023-12/bto-electrochromic-window-report-121123.pdf). The Department of Energy has set 2030 targets of a $6.50 per square foot installed price premium for residential dynamic windows and $11.80 for commercial, with SHGC performance of 0.05/0.65 (tinted/clear); meeting these targets would allow savings of 0.62 quads in the residential sector and 0.15 quads in the commercial sector[2](https://www.energy.gov/sites/default/files/2023-12/bto-electrochromic-window-report-121123.pdf).
Newer approaches aim at that cost gap. Tynt Technologies is developing dynamic windows based on reversible metal electrodeposition, in which metal is plated onto and removed from a transparent electrode, targeting a cost below $20 per square foot against the more than $50 per square foot of current electrochromic metal-oxide products from View, Sage, and Halio[11](https://www.energy.gov/cmei/buildings/articles/dynamic-windows-using-reversible-metal-electrodeposition). A related DOE-funded project demonstrated 25 cm² devices with minute-long switching times that maintained high optical contrast over at least 5,500 cycles[4](https://www.energy.gov/cmei/buildings/articles/robust-large-scale-dynamic-windows-using-reversible-metal-0).
## Non-energy benefits and applications
Electrochromic glazing is used in offices, airports, and healthcare facilities. Companies including Google and Netflix have installed it in their headquarters[2](https://www.energy.gov/sites/default/files/2023-12/bto-electrochromic-window-report-121123.pdf). In a pilot at the [Children's Hospital of Philadelphia](https://www.edgepedia.org/childrens-hospital-of-philadelphia), 92% of hospital staff said patients were more comfortable in rooms with daylight access, and the Methodist Olive Branch Hospital reported a 35% peak-load HVAC reduction after installation[2](https://www.energy.gov/sites/default/files/2023-12/bto-electrochromic-window-report-121123.pdf). Automated tinting based on sun position and cloud cover can eliminate blinds in commercial facades[12](https://councilofinnovation.com/impact-stories/smart-dynamic-glass-iot-windows/).
## Research directions
Current research pushes beyond simple clear-to-dark switching. Dual-band and multi-band electrochromic devices modulate visible and near-infrared transmittance independently, so a window can block heat while admitting daylight; a tri-band WO3/VO2 device with controllable lithium-ion intercalation achieved three active optical states and higher simulated energy savings than commercial low-e glass in most climate zones[13](https://www.nature.com/articles/s41893-024-01349-z). [Life-cycle assessment](https://www.edgepedia.org/life-cycle-assessment) is also becoming central: one study reported manufacturing-stage emissions of 49.6 kg CO2-equivalent per square meter for an electrochromic window versus 76.05 kg CO2-equivalent per square meter for a conventional double-pane window, and lifetime operational savings of up to 5,608 MJ per glazing unit, an energy payback time of roughly 0.8 years[14](https://www.nature.com/articles/s43246-026-01361-0).
## References
1. [Better Windows, Better Outcomes: How Electrochromics Improve Health, Productivity, and Efficiency, U.S. Department of Energy](https://www.energy.gov/cmei/buildings/articles/better-windows-better-outcomes-how-electrochromics-improve-health)
2. [Electrochromic Window Report (PDF), U.S. Department of Energy Building Technologies Office](https://www.energy.gov/sites/default/files/2023-12/bto-electrochromic-window-report-121123.pdf)
3. [A Design Guide for Early-Market Electrochromic Windows, Lawrence Berkeley National Laboratory Windows & Daylighting Group](https://windows.lbl.gov/publications/design-guide-early-market)
4. [Robust Large-Scale Dynamic Windows using Reversible Metal Electrodeposition, U.S. Department of Energy](https://www.energy.gov/cmei/buildings/articles/robust-large-scale-dynamic-windows-using-reversible-metal-0)
5. [Dynamic Glazings & Advanced Coatings, Lawrence Berkeley National Laboratory](https://windows.lbl.gov/dynamic-glazings-advanced-coatings)
6. [Application issues for large-area electrochromic windows in commercial buildings, Solar Energy Materials and Solar Cells](https://www.sciencedirect.com/science/article/pii/S0927024801001015)
7. [A Systematic Review of the Most Recent Concepts in Smart Windows Technologies with a Focus on Electrochromics, Sustainability (MDPI)](https://www.mdpi.com/2071-1050/13/17/9604)
8. [Recent Progress in Liquid Crystal-Based Smart Windows: Materials, Structures, and Design, Laser & Photonics Reviews](https://onlinelibrary.wiley.com/doi/10.1002/lpor.202200207)
9. [Thermochromic Materials for Smart Windows: A State-of-Art Review, Frontiers in Energy Research](https://www.frontiersin.org/journals/energy-research/articles/10.3389/fenrg.2021.800382/full)
10. [A Dawning Day for Energy-Efficient Electrochromic Windows, Science@Berkeley Lab](https://www2.lbl.gov/Science-Articles/Archive/sabl/2007/Jan/electro-windows.html)
11. [Dynamic Windows Using Reversible Metal Electrodeposition, U.S. Department of Energy](https://www.energy.gov/cmei/buildings/articles/dynamic-windows-using-reversible-metal-electrodeposition)
12. [HVAC energy cost reduced by ~20% — Real Estate Use Case by View Inc., Council of Innovation](https://councilofinnovation.com/impact-stories/smart-dynamic-glass-iot-windows/)
13. [Tri-band electrochromic smart window for energy savings in buildings, Nature Sustainability](https://www.nature.com/articles/s41893-024-01349-z)
14. [Spectral engineering of electrochromic smart windows for energy-efficient buildings, Communications Materials](https://www.nature.com/articles/s43246-026-01361-0)
15. [SPD SmartGlass - SmartGlass](https://www.smartglassinternational.com/news/spd-smartglass/)
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*Topic: Encyclopedia › Technology and the built world › Architecture, buildings, and civil works › Architectural knowledge and practice › Construction practice and materials*
*Initially written Sep 17, 2026 · Reviewed: Sep 30, 2026; Oct 15, 2026 · Edited: Sep 30, 2026; Oct 15, 2026 · Last review: Oct 15, 2026*
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