Vielight Lab | Measuring Actual Transcranial Irradiance with Human Tissue Models
In the rapidly growing world of brain photobiomodulation (PBM), consumers are often met with impressive claims. Manufacturers of 1070nm helmets frequently promise “deep brain penetration” based purely on the theoretical properties of the wavelength.
But theory is not physics.
At Vielight, we believe in validating our technology not just with marketing claims, but with rigorous laboratory testing. Recently, we took a critical question to the photonics lab: How much light energy actually makes it through a human skull?
The Experiment: Real Skull, Real Physics
To find the answer, we conducted a comparative irradiance test designed to replicate the rigorous methodology recently published by the PBM Foundation and Megalab.
Unlike standard tests that measure light at the source (the LED itself), this experiment introduced the formidable biological barriers that light must overcome to be effective.
Our Methodology Included:
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A Real Human Calvaria: An ethically sourced adult male skull to replicate the exact density and scattering properties of human bone.
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Optical Skin Phantoms: Synthetic tissue designed to mimic the absorption and scattering coefficients of the human scalp.
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NIST-Traceable Equipment: Using a Gentec-EO Power Meter and Optosky Spectrometer for precise, calibrated measurements.
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CCD Camera Visualization: A calibrated digital beam-profiling camera to generate live heatmaps of energy transmission.
We tested the Vielight Neuro Pro 2 against two popular consumer devices: the Neuronic Neuradiant and the Suyzeko 1070 Helmet.
The Data: The “Power Gap” Revealed
The results were stark. While many devices emit the correct wavelength, they lack the irradiance (power density) required to punch through the bone.
A 2024 systematic review that screened 2,133 records and included 97 brain-PBM studies reports that irradiance (power density) was typically ~250 mW/cm² with a wavelength of 810nm. This is because getting light energy through the skull, skin and cerebral spinal fluid requires a lot of energy and an appropriate wavelength (high dosimetry) to trigger beneficial neurophysiological effects.
The following table summarizes the peak irradiance measured at the surface (before the skull) versus the transmitted irradiance (what actually reached the brain side of the skull).
| Device Tested | Surface Irradiance (Source) | Transmitted Irradiance (Through Skull) | CCD Camera Visibility |
| Vielight Neuro Pro 2 | ~300 – 400 mW/cm² | ~4.0 mW/cm² | ✅ Visible |
| Neuronic Neuradiant | ~11 mW/cm² | ~0.075 mW/cm² | ❌ Not visible |
| Suyzeko 1070 Helmet | ~11 mW/cm² | ~0.075 mW/cm² | ❌ Not visible |
Key Takeaway:
These results are before blood and water are taken into account, above 1000nm, water becomes the primary chromophore, not mitochondria, which greatly attenuates light energy. As shown in the data, the competitor helmets delivered less than 0.1 mW/cm² through the skull—a value so low it fell below the reliable detection threshold of our spectrometer. The photons were almost entirely absorbed or scattered by the bone.
In contrast, the Vielight Neuro Pro 2, which utilizes high-power micro-chip LEDs designed to simulate laser parameters, successfully delivered ~4.0 mW/cm² to the other side of the barrier.
Methodology: Replicating the “Gold Standard” of PBM Testing
To ensure our results were both accurate and clinically relevant, we designed this experiment to replicate the rigorous testing protocols utilized by Megalab Group Inc. and Optronic Laboratories in their recent 2024 independent reports.
Most consumer PBM devices are tested by measuring the LED output directly at the source (the bulb). While this provides a theoretical “max power” number, it completely ignores the physics of biology: light must pass through skin, bone, and fluid before it interacts with the brain.
Our methodology introduced these biological variables to measure actual transcranial delivery.
1. The Biological Barriers
To simulate real-world conditions, we utilized two primary barriers:
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Human Calvaria (Skull): A real, ethically sourced adult male skull from Osta International. This provides the exact calcium density, thickness, and scattering properties of a living human head.
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Optical Skin Phantom: A synthetic tissue model sourced from QUEL Imaging, engineered to mimic the specific absorption and scattering coefficients of the human scalp.
2. Precision Instrumentation
We employed NIST-traceable, medical-grade photonics equipment to capture the data:
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Spectrometer: Optosky ATP 2000P – Used to verify the exact spectral emission (wavelength) of each device.
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Power Meter: Gentec-EO Silicon Photodiode Power Meter – A high-sensitivity sensor used to measure optical power (Watts) and convert it into irradiance mW/cm2 using a 1mm pinhole aperture.
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Beam Profiling: A calibrated Digital CCD Camera was used to capture the visual “energy footprint” and generate live heatmaps of light transmission.
3. The Testing Protocol
The experiment followed a strict three-stage procedure for each device (Vielight Neuro Pro 2, Neuronic Neuradiant, and Suyzeko 1070 Helmet):
- Stage 1: Baseline Characterization (The Input)
We first measured the “raw” output of the device directly at the emission surface. This established the maximum possible irradiance πr2 before any attenuation occurred.
Power (mW) is divided by the Area (cm2)
Area = πr2 = 3.14159*(0.1)2 = 0.00785 cm2
Example with 3 mW measured with the power meter.
Irradiance = 3 mW / 0.00785 cm2 = 382 mW/cm2 - Stage 2: Attenuation Measurement (The Barrier)
The human calvaria and skin phantom were placed directly in the optical path between the device and the sensor. We then measured the transmitted irradiance—the amount of light that successfully exited the underside of the skull. This step reveals the “attenuation ratio,” or how much energy is lost to the bone. - Stage 3: Visual Fluence Mapping (The Proof)
Using the CCD camera, we filmed the interior of the skull in real-time while the devices were active. This generated a visual heatmap, allowing us to “see” if any photons were actually penetrating the bone to reach the area where the brain would be.
Why This Methodology Matters:
Standard industry tests often rely on calculated (theoretical) values that assume 100% transmission. By physically placing a human skull in the path of the light, we convert theoretical marketing claims into observable physical reality.
Why Irradiance is Critical
In PBM, Irradiance is just as critical as Wavelength.
Think of the skull as a thick, heavy door. The Wavelength (810nm or 1070nm) is the key that fits the lock. But Irradiance is the strength of the hand turning that key. You can have the perfect key, but if you don’t have the power to turn it, the door stays shut.
Our data proves that low-power LEDs (standard in most helmets) simply do not have the energy to “turn the key” and overcome the skull’s natural attenuation.
The Intranasal Advantage: Bypassing the Barrier
While this experiment highlighted the difficulty of transcranial (through the skull) delivery, it also underscores the genius of the intranasal delivery method.
Even with high-powered LEDs, the skull remains a significant obstacle. This is why the Vielight Neuro system includes a patented Intranasal Applicator.
By delivering light through the nasal cavity, we target the ventral brain through the cribriform plate—a thin, porous bone structure that offers a direct, low-resistance pathway to the brain. This “backdoor” route allows for significant photonic delivery to the underside of the brain, complementing the transcranial stimulation.
See the Evidence Yourself
Transparency is the bedrock of science. We invite you to watch the full video of our laboratory test to see the methodology, the real-time data readings, and the CCD heatmaps for yourself.
Further Reading:
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PBM Foundation & Optronic Lab Report: [Link]
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Clinical Data on Intranasal Efficacy (Baycrest Hospital): [Link to Baycrest Study]