What is irradiance?
Irradiance refers to the power of light emitted per unit area and is usually measured in milliwatts per square centimeter (mW/cm²). In red light therapy, it plays a crucial role in determining how much light energy reaches the target tissue. This affects the penetration depth, the dose, and the overall effectiveness of the therapy.
Precise measurement of radiation intensity is essential to ensure the effectiveness, safety and consistency of the therapy – whether it concerns skin rejuvenation, pain relief, muscle regeneration or other applications.
Irradiance is a fundamental factor that guides both the design of the devices and the usage recommendations. If the irradiance is too low, the therapy is often ineffective because too little light reaches the target tissue. If it is too high, overheating and tissue damage can occur, impairing effectiveness. Therefore, it is essential to find the right balance to achieve maximum benefits while maintaining safety.
How is irradiance measured?
Precise measurement of irradiance is an essential component of red light therapy. Two main measuring devices are used for this purpose:
-
Solar meter (broadband power meter):
-
Measures total light output across a broad spectrum without distinguishing between specific wavelengths.
-
It often delivers higher values, almost twice as high as those measured with spectrometers. This is because it also detects irrelevant wavelengths outside the therapeutic range.
-
Although simple and inexpensive, it is unsuitable for red light therapy due to a lack of precision.
-
-
Spectrometer (spectral power meter):
-
Provides detailed spectral information and measures irradiance specifically for wavelengths such as 630, 660, 670, 810, 830 and 850nm.
-
It is considered an industry standard because of its accuracy and ability to isolate therapeutic wavelengths from irrelevant ones.
-
heilys relies on spectrometer measurements to ensure reliable and consistent performance data.
-
Comparison of the irradiance of red light therapy with sunlight
Understanding how red light therapy devices compare to natural sunlight helps clarify why extremely high irradiance levels can be unnecessary and potentially harmful. The therapeutic energy field of sunlight, particularly in the red and near-infrared ranges, is significantly lower than that of many artificial devices.
| light source | Total irradiance (mW/cm²) | Radiation intensity in the therapeutic range (600-900nm) (mW/cm²) |
|---|---|---|
| Sunlight (midday sun) | ~100 | ~20-30 |
| Optimal area for red light therapy | 40-100 | 40-100 |
| Excessive irradiance | >100 | >100 |
Natural sunlight provides approximately 100 mW/cm² of total irradiance on a clear day. However, the therapeutic range of red and near-infrared light (600-900 nm) accounts for only a fraction of this total energy, typically around 20-30 mW/cm² .
Optimal range according to studies
-
General consensus: Studies show that red and NIR light therapy is most effective when applied at a power of 20-200 mW/cm² .
-
Superficial applications: For superficial applications such as skin health, anti-aging and wound healing, irradiance levels of 20-50 mW/cm² are often effective.
-
Deep tissue treatments: For deeper tissues (muscles, tendons, joints), a higher irradiance of 70-100 mW/cm² is recommended, as this allows sufficient energy to penetrate into the interior of the body.
Why extremely high radiation intensities should be used with caution
Higher radiation intensities can penetrate deeper into tissue and shorten treatment times, but there is a natural limit to how much energy cells can absorb. Think of your cells like tiny batteries: If they are charged too quickly or with too much power, it can be counterproductive.
Extremely high irradiance levels (over 100 mW/cm² ) can lead to overheating, tissue damage, or reduced therapeutic effects. Furthermore, excessive tissue heating can compromise the effectiveness of red light therapy, which can promote cell regeneration and reduce inflammation.
If higher radiation intensities are used, this should only be done with professional advice and at short intervals. Overdoing it is definitely not advisable.
Why the right balance is crucial
Instead of simply striving for the highest possible irradiance, it is more important to choose a device that operates within the optimal range for the specific application. Using a spectrometer ensures that the power is measured accurately and is consistent with natural biological processes.
Understanding the principles of radiation intensity will help you make better decisions and get the most out of your red light therapy. heilys ® devices have been developed with this knowledge to achieve exactly that.
