Why Do Two Pairs of Glasses From The Same Company Differ—one Showing Full Color, While The Other Retains Only Green?

Place the Thunderbird X3 Pro side-by-side with the newly released iO, and a set of intriguing figures emerges.

The X3 Pro features a full-color binocular display; it launched at a starting price of 8,999 yuan and weighs 76 grams. The iO utilizes a monochromatic green display; it debuted at 2,349 yuan and weighs 34 grams.

One device leans closer to a full-fledged spatial computing system, while the other resembles a standard pair of glasses. Although they originate from the same company, they have not followed the same development path.

The most obvious conclusion might be that full-color technology is simply too expensive and heavy, necessitating a green-only approach for the time being.

However, that is only half the story. Price and weight reflect the device's total cost and mass—factors that also encompass the processor, cameras, speakers, storage, and spatial tracking capabilities—so these figures cannot be attributed solely to the display color.

To truly understand the distinction between these two pairs of glasses, one must look at a more detailed breakdown of the optics.

First, separate the general ledger from the subsidiary ledgers.

Let’s first look at the overall device specifications.

The X3 Pro features the Snapdragon AR1 chip, 4GB of RAM and 32GB of storage, a main camera, a spatial camera, and speakers; it also supports map navigation and application interfaces. The product definition for the iO model is significantly more focused: it lacks cameras and speakers, prioritizing instead subtitles, teleprompting, translation, notifications, and information displays.

Therefore, the 42-gram difference between the 76g and 34g devices cannot be simplistically attributed to the addition of full-color capabilities. Similarly, the price gap—8,999 yuan versus 2,349 yuan—represents far more than just a color upgrade.

When we examine the optics, the true cost of adding color becomes apparent.

RayNeo has announced that the volume of the X3 Pro’s "Firefly" full-color optical engine is 0.36 cc, whereas the iO’s "Firefly Nano" monochrome green optical engine measures 0.085 cc.

Dividing 0.36 by 0.085 yields a ratio of approximately 4.2.

While this does not constitute a strict "apples-to-apples" comparison—given that the two optical engines differ in release timing, packaging constraints, and performance targets—the publicly released specifications from the same company do illustrate the scale of the difference: the primary "margin" gained by opting for monochrome green is in the volume of the optical engine itself.

Why green, of all colors?

If only one color is to be retained, why choose neither red nor blue?

Two distinct factors must be considered here: device efficiency and perceived brightness; these should not be conflated.

The device efficiency of blue MicroLEDs is not inherently lower than that of green ones. Woo et al. fabricated circular mesa structures ranging from 3 to 150 μm in diameter using one blue wafer and two green wafers of differing quality. For diameters exceeding 5 μm, the blue sample exhibited higher absolute photoluminescence (PL) efficiency than green sample 1. It was only at the 3 μm scale that green sample 1 surpassed the blue sample. Green sample 2, meanwhile, showed lower efficiency than the blue sample across all tested sizes.

Even within the green spectrum, efficiency curves can vary significantly. The efficiency ranking after miniaturization depends on the interplay between the wafer's intrinsic efficiency and surface recombination; one cannot draw conclusions based solely on the emission color.

Let’s also consider the human eye factor. The CIE photopic luminous efficiency function peaks near 555 nm. This means that, in a theoretical comparison where other conditions remain constant, light near this wavelength is more effectively converted into perceived visual brightness.

Green light falls squarely within the region of high sensitivity for human photopic vision. When displaying elements like subtitles, arrows, or brief notifications, a monochromatic green setup offers a more efficient balance between readability and optical power utilization.

Red light faces additional practical constraints. As AlGaInP red MicroLEDs are miniaturized, the impact of sidewall non-radiative recombination on efficiency intensifies; research papers frequently cite the efficiency gap between red and blue/green LEDs as a critical challenge.

This does not necessarily mean that green MicroLEDs possess the highest device-level efficiency. Actual system performance depends on a combination of factors: light-emitting chip efficiency, optical engine light capture, waveguide diffraction efficiency, and human eye response. Furthermore, since the specific emission wavelength of the iO device has not been disclosed, one cannot simply substitute the 555 nm peak value for the actual product specifications.

Therefore, a more accurate assessment is this: a monochromatic approach eliminates the need for two additional light channels, while the choice of green aligns the output with the human eye's peak sensitivity. It is a system-level equation involving chip technology, optics, and human physiology—not merely a simple comparison of which chip type boasts the highest External Quantum Efficiency (EQE).

Optical-Mechanical Layout: Full-color configuration featuring two additional optical paths and a single color-combining stage.

The X3 Pro’s full-color optical engine utilizes red, green, and blue MicroLED channels, superimposing the three images onto a single optical axis via a color-combining prism.

In contrast, a monochrome green system handles only a single light path.

It is not merely a matter of eliminating two micro-display panels; full-color systems must also contend with color-combining prisms, the alignment of three optical axes, cross-color white balance, and color consistency across temperature fluctuations. When scaling up to a binocular system, these component and calibration requirements must be replicated for both the left and right eyes.

Therefore, miniaturizing a full-color optical engine requires looking beyond the size of the display screen itself; the projection lens, prism, structural components, and assembly tolerances located behind the screen all consume valuable space within the temple arm.

This explains why, even though a 0.36 cc full-color optical engine is already remarkably compact, iO is still developing a 0.085 cc monochrome green "Nano" engine.

For a product aiming to resemble standard eyewear, every bit of volume saved within the temple arm can be reallocated to the battery, structural integrity, weight balancing, and aesthetics.

Waveguide Ledger: Missing one color means missing an entire set of constraints.

After the optical engine generates an image, the waveguide must deliver that image to the user's eye.

Diffractive waveguides rely on micro-nano gratings to alter the direction of light propagation. Since wavelength is a direct factor in the grating equation, red, green, and blue light do not naturally align in terms of propagation angle or diffraction efficiency when encountering the same grating.

There are two typical approaches to achieving full-color display. The traditional method assigns different waveguide layers to different colors, though this comes at the cost of increased thickness and assembly complexity. The alternative is to multiplex multiple grating periods into a single waveguide; while this allows for a thinner product, it shifts the design burden onto factors such as color uniformity, crosstalk, ghosting, efficiency, and manufacturing tolerances.

The X3 Pro has successfully implemented full-color display within a single-layer etched diffractive waveguide, demonstrating that full-color capability does not necessitate stacking three separate lenses.

The value of a single-green configuration lies in more than just the elimination of a glass layer. It removes the design challenge of cross-wavelength matching, allowing the engineering team to concentrate optimization efforts on the eyebox, brightness uniformity, light transmission, light leakage, and aesthetics.

However, a single-green configuration certainly does not imply a simpler waveguide design. Publicly available information from iO depicts three optical components in a single exploded-view diagram, while also noting a 1:1 thin, lightweight fit with the user's prescription lenses. Subsequent official fitting instructions further clarify that iO’s refractive elements are directly integrated with the display optics.

Therefore, the "three layers" mentioned here should be interpreted as a lens assembly rather than three independent waveguides. As public materials do not label the material and function of each layer, it remains unclear which serves as the protective lens and which as the prescription lens.

Single-green waveguides still require addressing issues such as eyebox, brightness uniformity, light transmission, light leakage, and rainbow artifacts; however, these challenges are inherent to the waveguide itself and do not stem from the three-layer structure.

A single-green configuration does not eliminate every challenge; rather, it removes the single most costly variable.

The colors on the shelves are determined first by the task.

Once the trade-offs for the optical engine and waveguide are fully calculated, revisiting the product definition reveals a clear, logical progression.

The X3 Pro needs to display color maps, app interfaces, photos, and spatial content. Color itself conveys information; removing it would significantly compromise the product's capabilities.

The iO, meanwhile, primarily displays subtitles, teleprompter text, translations, schedules, and brief notifications. These require content that is instantly readable at a glance; the marginal value added by color is far lower than that of factors like weight, light transmittance, battery life, and price.

Therefore, the engineers didn't simply decide on green and then scramble to find features that fit it.

The process worked the other way around: the product was defined to handle only high-frequency, low-density information, making "monochrome green" the logical choice.

This is precisely where the value of these two pairs of glasses lies. Instead of forcing a single device to cover every possible scenario, the company split spatial computing and everyday information display into two distinct products.

When will it get back to around 34 grams?

Full-color technology has not been ruled out from an optical standpoint.

In 2025, a team led by Chen (from Westlake University and other institutions) published a paper in eLight detailing a prototype of a single-layer, full-color silicon carbide diffractive waveguide. The official report cited a 30.82° field of view, a thickness of 0.75 mm, and a weight of 3.795 g for the single-piece unit, while demonstrating full-color imaging free of rainbow artifacts.

These results prove that it is possible to manufacture a very thin, full-color waveguide. Although the paper demonstrated 4-inch wafer-level processing and the integration of corrective Fresnel elements, it did not disclose data regarding batch yields, end-to-end costs, or device-level reliability—metrics essential for mass production in consumer electronics. While the approach is viable, this does not mean that a 34-gram full-color product is yet market-ready.

Another path of development lies within the optical engine. If full-color MicroLED technology can evolve from a three-panel-plus-prism setup to a truly mature monolithic RGB design, the structural burden associated with combining three color channels will be reduced.

Therefore, to determine when green will cease to be the default choice for lightweight smart glasses, one should monitor three factors:

1. Whether the volume and power consumption of full-color optical engines can approach those of single-green engines while maintaining the same aperture size.

2. Whether single-layer full-color waveguides can simultaneously deliver satisfactory efficiency, uniformity, eye-box size, yield rates, and cost-effectiveness.

3. Whether applications on the glasses actually require color—and whether users are willing to accept the trade-offs in power consumption and weight that color entails.

All three conditions must be met.

Returning to the beginning: the X3 Pro aims to pack a spatial computing system into the device as fully as possible, whereas the iO seeks to retain a display function while looking as much like ordinary glasses as possible. The former opted for full-color, while the latter chose green; both decisions stem from their respective product definitions.

The real question has never been whether color is technically feasible.

Rather, the question is whether the device can still feel like a pair of glasses once color is incorporated.

Source: AR Insights