Edward Tang | Avegant: Why does etendue mismatch cause MicroLEDs to instantly lose up to 94% of their light in diffractive AR waveguides?
00:07:16 - 00:09:05
Other snippets from this talk
Summary of the clip:
Why does etendue mismatch cause MicroLEDs to instantly lose up to 94% of their light in diffractive AR waveguides?
A major, often overlooked bottleneck in AR display efficiency is etendue—the fundamental thermodynamic product of a light source's emission angle and emission area. Because etendue is a conserved quantity that cannot be reduced by passive optics, matching the etendue of the display engine to the narrow acceptance aperture of a diffractive waveguide's input coupler is critical.
Due to this severe mismatch, current MicroLED light engines suffer an immediate, unrecoverable optical loss of approximately 94% before the light even propagates down the waveguide. This massive etendue mismatch places a hard theoretical ceiling on MicroLED system efficiency, forcing the LEDs to run hotter and pull more power to achieve daylight-readable brightness.
LCoS engines avoid this devastating thermodynamic penalty by employing a completely decoupled illumination architecture where the light source is independent of the imaging panel. This separation allows optical designers to meticulously size the illumination LEDs to perfectly match the waveguide's etendue, achieving far higher theoretical coupling efficiencies and enabling flexible tuning for varying eyebox and pupil sizes.
In this short video, you can learn:
* The physical definition of etendue and why it acts as an unyielding thermodynamic limit on AR display system efficiency.
* Why MicroLED architectures inherently suffer from a 94% etendue mismatch loss when coupling into standard diffractive waveguides.
* How separating the illumination path from the imaging panel in LCoS engines allows for perfect etendue matching and higher system efficiency.
📋 **Clip Abstract** This clip explains the physics of etendue and its critical role in determining the efficiency of AR light engines coupled to diffractive waveguides. Edward Tang highlights how MicroLEDs lose 94% of their light due to etendue mismatch, while LCoS engines leverage decoupled illumination paths to optimize light transmission.
#EtendueMismatch, #DiffractiveWaveguides, #MicroLEDEngines, #LCoSLightEngines, #AugmentedRealityOptics, #MicrodisplayTechnology
This is a highlight of the presentation:
AR’s Display Dilemma - LCoS v MicroLED
More Highlights from the same talk.
01:56 - 03:19
Why is one watt the absolute thermal and power limit for consumer AR glasses?
Why is one watt the absolute thermal and power limit for consumer AR glasses?
Data and research show that consumer AR glasses cannot exceed about 50 grams if they are to be all-day wearable. Above 50 grams, the device becomes a short-term use product, worn for an hour or two, and loses the ability to replace your everyday glasses. Hitting that number is incredibly difficult given all the components that must go into the glasses.
The second constraint is the thermal budget. Devices cannot get too hot: too hot means discomfort or, worse, a safety issue that may burn your skin. Typically you want to stay below 50 degrees, and ideally below about 43 degrees, for the device to be safe and comfortable. Combined with the 50-gram limit, this creates a serious thermal dissipation challenge.
With a 50-gram limit, you cannot put fans in these devices, and you can't really put heat sinks in them either: they are too small and too light, and there is no way to get airflow through the system. That is where the one watt number comes from, as about the maximum thermal dissipation limit achievable through a pair of glasses while keeping them small, lightweight and consumer-friendly.
In this short video, you can learn:
* All-day wearable consumer AR glasses must not exceed about 50 grams, or they degrade into one-to-two-hour short-term use devices.
* Device temperatures must stay below 50 degrees, and ideally below about 43 degrees, to remain comfortable and avoid burning skin.
* Because a 50-gram device cannot use fans, heat sinks or airflow, roughly one watt is its practical thermal dissipation ceiling.
📋 **Clip Abstract** Consumer AR glasses face two hard ceilings: about 50 grams of mass for all-day wear, and skin-safe surface temperatures below 50 degrees, ideally about 43 degrees. Because a device that small and light cannot host fans, heat sinks or airflow, those limits converge on roughly one watt of maximum thermal dissipation.
About the speaker:
* Speaker: Edward Tang
* Company: Avegant Corp.
* Event: Eindhoven 2026
* Location: High Tech Campus, Eindhoven
#50GramWeightLimit, #ThermalDissipationCeiling, #PassiveCooling, #SkinTemperatureLimit, #AugmentedReality, #SmartGlasses
12:22 - 14:44
How can shrinking the light engine's pupil size more than double waveguide coupling efficiency?
How can shrinking the light engine's pupil size more than double waveguide coupling efficiency?
Pupil size is a really important knob. Light engine efficiency and waveguide efficiency are usually assessed separately, yet what actually matters is milliwatts to the glasses to nits to the eye. That means treating the light engine and the waveguide together, as one system, and accounting for the losses at the interface between them. Co-optimising that interface is where the gains hide.
The input to a waveguide is not uniformly efficient. One side is very inefficient, because light has to travel multiple bounces through that input pupil, and every time it touches it, a lot of light is lost. Other areas are highly efficient: light enters the input pupil and couples immediately into the waveguide without secondary interactions. Shrinking the pupil lets the engine target the efficient regions.
A typical microLED system has a pupil of three and a half to four millimetres. Assuming about 1,000 nits per lumen at that pupil size, simply reducing pupil size lifts waveguide efficiency by 50%; moving from unpolarised to polarised light adds another 50%. That means more than doubling waveguide efficiency. And a smaller pupil allows a thinner waveguide, cutting weight and freeing budget for lighter glasses or more battery.
In this short video, you can learn:
* Reducing pupil size raises diffractive waveguide coupling efficiency by 50%, and polarised light versus unpolarised contributes another 50%.
* Waveguide input pupils are non-uniform: one side loses light to repeated bounces while other regions couple immediately with no secondary interactions.
* A smaller light engine pupil also permits a thinner waveguide, reducing weight and leaving budget for lighter glasses or more battery.
📋 **Clip Abstract** Pupil size controls how much light the light engine actually delivers to the eye, because waveguide input pupils are unevenly efficient. Co-optimising the light engine pupil with the diffractive waveguide — shrinking it from three and a half to four millimetres and polarising the light — can more than double waveguide efficiency while thinning the waveguide.
About the speaker:
* Speaker: Edward Tang
* Company: Avegant Corp.
* Event: Eindhoven 2026
* Location: High Tech Campus, Eindhoven
#WaveguideCouplingEfficiency, #PupilSizeReduction, #DiffractiveWaveguides, #MicroLEDLightEngine, #AROptics, #NearEyeDisplays
08:29 - 10:16
How does average pixel level (APL) expose color microLED power limits versus LCOS?
How does average pixel level (APL) expose color microLED power limits versus LCOS?
The graph tracks display power consumption against average pixel level. Color microLED systems, because of inefficiencies, thermal efficiencies, EQ issues and etendue problems, can really only operate at low APLs, typically well under 10% APL if they must stay within the right power constraint or power budget. LCOS today is efficient enough to operate across all APLs within the needed power budget, which helps explain why companies outside China, such as Meta or Snap, already ship LCOS displays.
Traditional LCOS systems do not benefit from low APL in the same way. They illuminate the entire image very uniformly, so power is pretty much flat with content. That creates an intersection point between the two display technologies on the power-versus-APL graph. This power intersection point typically happens under about 10% APL. Below that level, color microLED power constraints are severe; above it, LCOS can keep operating within the required budget without APL limitations.
The good news is that efficient LCOS technology is already a shipping answer. For a high-resolution, full-color display with no APL limitations, LCOS is available today. It avoids the low-APL restriction that constrains color microLED light engines under the power budget. That makes LCOS the practical choice when small, lightweight glasses require performance across content. This is not a future promise but an existing display path for full-color images.
In this short video, you can learn:
* Color microLED systems can typically operate only well under 10% APL to stay inside the required power budget.
* LCOS operates across all APLs within the needed power budget and delivers full-color images with no APL limitations.
* The power intersection between LCOS and color microLED typically happens under about 10% APL, and Meta and Snap already ship LCOS displays.
📋 **Clip Abstract** Average pixel level determines whether a display stays inside the power budget: color microLED systems are limited to low APLs, typically well under 10%, due to inefficiencies, thermal efficiencies, EQ issues and etendue problems. LCOS operates across all APLs, and companies outside China such as Meta or Snap already ship LCOS displays for full-color images with no APL limitations.
About the speaker:
* Speaker: Edward Tang
* Company: Avegant Corp.
* Event: Eindhoven 2026
* Location: High Tech Campus, Eindhoven
#AveragePixelLevel, #LCOSDisplays, #ColorMicroLED, #PowerIntersection, #ARDisplays, #LightEngines