In brain photobiomodulation, near-infrared (NIR) light within the 810\u20131100 nm wavelength range offers beneficial cellular effects and deep tissue penetration. However, if the wavelength is optimal but the irradiance (surface power density) is too weak, penetration will be minimal or nonexistent.<\/span><\/strong><\/p>\n The two most critical factors<\/strong> determining the efficacy of this therapy are irradiance (surface power density)<\/strong> and wavelength<\/strong>, which determine depth and cellular effects. This article explores the significance of these metrics and why brain PBM requires a higher irradiance than natural sunlight to achieve its unique benefits.<\/p>\n Irradiance, measured in milliwatts per square centimeter (mW\/cm\u00b2), refers to the concentration and intensity of light energy delivered to a specific area.<\/p>\n For comparison, natural sunlight in the near-infrared (NIR) range is free and typically has an irradiance of 50-100 mW\/cm\u00b2 at the Earth\u2019s surface. While sunlight exposure provides some level of photobiomodulation\u2014notably through NIR light\u2014its diffuse nature and accessibility already makes it a routine part of daily life for most people. To provide a meaningful therapeutic advantage, brain photobiomodulation devices must deliver higher irradiance levels than sunlight, ensuring benefits beyond what can be achieved through standard sunlight exposure.<\/span><\/strong><\/p>\n A\u00a02024 systematic review<\/strong><\/a>\u00a0that screened 2,133 records and included 97 brain-PBM studies reports that irradiance (power density) was typically\u00a0~250 mW\/cm\u00b2<\/strong>. The Vielight Neuro slightly exceeds the irradiance used in these studies, which included lasers. Optimal irradiance ensures that enough light energy reaches the neurons, stimulating mitochondrial activity, increasing ATP production, and supporting neurogenesis and synaptic plasticity.<\/p>\n<\/div><\/div><\/div><\/div><\/div> Brain PBM devices should be designed to deliver focused, high-irradiance light directly to the head within the NIR range and bypass hair, to e<\/span>nsure benefits beyond what can be achieved through standard sunlight exposure<\/span>. The Vielight Neuro, which is supported by the most published brain photobiomodulation studies<\/a> across a wide variety of fields has an irradiance exceeding 200 mW\/cm\u00b2 to ensure sufficient energy reaches neural tissues.<\/p>\n In published studies, higher irradiance levels enable targeted stimulation of mitochondrial activity, leading to enhanced cognitive function, improved mood, and potential therapeutic effects for conditions like Alzheimer\u2019s disease, Parkinson’s Disease and traumatic brain injury. Higher irradiance levels also enable full transcranial coverage<\/a> with fewer LEDs.<\/p>\n A\u00a02024 systematic review<\/strong><\/a>\u00a0that screened 2,133 records and included 97 brain-PBM studies reports that irradiance (power density) was typically\u00a0~250 mW\/cm\u00b2<\/span><\/strong>. This is because getting light energy through the skull, skin and cerebral spinal fluid requires a lot of energy and an appropriate wavelength to trigger beneficial neurophysiological effects.<\/p>\n As part of their testing program to standardize irradiance reporting, the PBM Foundation<\/a> benchmarked the Vielight Neuro 3<\/strong> against two PBM helmets \u2014 the Suyzeko NIR helmet<\/strong> and the Neuronic Neuradiant<\/strong> \u2014 in collaboration with two photonics engineering firms. Both MegaLab<\/strong> and Optronic Lab<\/strong> conducted independent tests, yielding strongly similar and replicable results<\/p>\n MegaLab<\/a>\u00a0and\u00a0Optronic Lab<\/a>, photonics engineering firms, conducted two mutually exclusive tests with strongly similar results:<\/p>\n Based on the 2024 systematic review<\/strong><\/a> of 97 brain-PBM studies, the Vielight Neuro (180-350 mW\/cm2<\/sup>) is inline with the 250 mW\/cm2<\/sup> \u00a0average<\/strong>, which included lasers. The Neuronic and Suzyeko helmets only generated less than 5%<\/strong> of the 250 mW\/cm2<\/sup> \u00a0average.<\/p>\nUnderstanding Irradiance in Photobiomodulation<\/h3>\n
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![](\"https:\/\/www.vielight.com\/wp-content\/uploads\/2025\/01\/Vielight-Skull-Neuro-NIR-Irradiance-Penetration-and-Scattering-v2.jpg\" "\\"Vielight-Skull-Neuro-NIR-Irradiance-Penetration-and-Scattering-v2\\"")
<\/span>Figure - Near-invisible 810nm NIR energy capture of Vielight Neuro using photosensitive equipment, Department of Bioengineering, Uniformed Sciences University<\/h2><\/div><\/div><\/div>
Why Brain PBM Needs a Higher Irradiance than Sunlight<\/h3>\n
Irradiance Measurement Case Study<\/h3>\n
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<\/p>\n![](\"https:\/\/www.vielight.com\/wp-content\/uploads\/2024\/07\/Published-peer-reviewed-studies-comparison.jpg\" "\\"Published-peer-reviewed-studies-comparison\\"")
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