We ran experiments to compare the emission signal strengths of the NIRsport and Octomon. Since these systems run in the Near IR, we experimented with some non-standard test equipment.
It was a fun experiment.
The NIRsport uses LED wavelengths of 760 nm and 850 nm. A typical spectral spread shows that only a few percent of total power is emitted more than 50 nm away from the spectral peak (Fig. 1). Since the upper end of visible light to the eye is 700 nm, the eye can see some of the light from the 760 nm LED, thus the system looks red when it is turned on. By far, most of the power is in the infrared and invisible to the eye.
A camera has red, green, and blue sensors. Usually the red sensor will also detect IR, unless there is a good-quality IR filter in front of the lens. So poor quality cameras may be better to detect near IR, and then IR sources may show up brighter in the camera image. Using an iPhone camera, the Octamon lights are much brighter than a red object (Figure 2), although the lights and camera look similarly colored red to the human eye. Thus, a phone camera detects some infrared.
Using the camera phone, the NIRsport emitter looks much brighter than the Octamon emitters, suggesting NIRsport puts out more IR power than the Octamon (Fig. 3).
More light power (the power is mostly in IR) may provoke more heating at the LED emitter, since there is some energy absorption when crossing the boundary from fiber to air. A thermal image (8000-14000 nm) shows that the NIRsport emitter generates more heat than the Octomon emitters (Fig. 4), suggesting that NIRsport is emitting more IR power.
Hmmm, makes you wonder if the Hitachi emitters start getting hot after 10 minutes?
Cross-checking with the actual NIRS equipment is better since they use real IR detectors. To check signal strength: put a finger in front of the Octamon detector, point a NIRsport or Octamon emitter through the finger to see which generates a higher response on the same detector. Possibly will find out that quality of contact is the most important factor.