The power density measurements in the above picture are produced by pointing the TES power meter at the second lamp from the bottom of the sauna. In this case, the power meter is mostly measuring the output from the lowest 3 lamps, so adding or removing the top 2 lamps does not affect the readings much due to the directional nature of the power meter. For comparison the picture below shows power density measurements for a single General Electric heat lamp. The readings are 33.57 mW/cm2 at 24 inch distance, 57.07 mW/cm2 at 18 inches, and 100.4 mW/cm2 at 12 inches.
Total Energy and Dosage:
Energy is a measurement expressed as Joules (J), and is equal to power density in Watts (W) over a specific amount of time. Dosage, also sometimes called fluence, represents the area of the body over which the energy is applied.
Total Energy (Joules) = Watts x Time( seconds)
Dosage = Joules/cm2
For example, looking at the Spectra sauna power density of 144.6 mW/cm2 at 12 inch distance, the dosage over 60 seconds can be calculated as follows, where 1 milliWatt = .001 Watts
Dosage = 144.6 mW/cm2 x 60 x .001 = 8.68 J/cm2
Biphasic Dose Response: Fact, Human Error, or Marketing Hype?
In the marketing literature for near infrared devices including LED light panels and laser devices, many times you will find claims about needing to get “just the right dose” of near infrared light and “avoid too much exposure”. This is usually called the biphasic dose response. Michael Hamblin, PhD is one of the leading researchers on near infrared light and has written several hundred articles on the subject. Here is what he has to say about dosage and the biphasic dose response.
“What we don’t really know is can you overdose the body on the total number of joules, or is it only when it’s
concentrated. It’s not common in humans, I have to say. Most of the studies showing a convincing biphasic dose response have been done in cells or animals. Ten minutes in a Novothor will give you 120000 joules of energy. An hour of sunbathing, and you will get a million joules of optical energy, because the area is in the hundreds of square centimeters.” – Michael Hamblin
“The sun is the source of heat and energy for the earth. The solar output on the earth is called the power density. The power density of the sun’s radiation on the surface of the earth is approximately 1.4 kW/m2. This value varies slightly throughout the year but by no more than 0.1 percent. One reason for this variation is the changing earth-sun distance. This distance varies by about six percent throughout the year, causing the power density to range from about 1.308 kW/m2 to 1.398 kW/m2.”
Let us convert the high end number 1.398 kW/m2 to mW/cm2, where 1 Watt = .001 kW, and W/m2 x .1 = mW/cm2.
Power density of the sun at sea level = 1.398 kW/m2 = 1398 W/m2 = 139.8 mW/cm2
Power density of the Spectra sauna at 12 inch distance = 144.6 mW/cm2
Are you afraid of the sun? Is the biphasic dose response a case of fact, human error, or marketing hype? Does it only apply to laser and LED devices? The reader is welcome to come to their own conclusions.