Schroeder et al indicate up to 65% of Near IR are capable of reaching through the epidermis and up to 2 microns deep into the dermis. Beyond 2 microns the skin is impenetrable to all types of Infrared. Transmission must not be confused with absorption in terms of heat effectiveness. Because of the very high temperatures of shortwave infrared, the high transmission rate can cause damage through greater penetration of the skin and a lower rate of absorption.

Skin absorbs heat principally because of its 80% water content (Robinson 2014), making Medium/Far and Far Infrared the most biologically significant band for heat absorption and this translates to “more effective heating” by heaters peaking in these bands.

Agresti, A. and Finlay, B.  (2008)  Statistical Options for the Social Sciences, 4th edition.  (Upper Saddle River, NJ: Prentice Hall).

BetterEvaluation is part of the Global Evaluation Initiative, a global network of organizations and experts supporting country governments to strengthen monitoring, evaluation, and the use of evidence in their countries. The GEI focuses support on efforts that are country-owned and aligned with local needs, goals and perspectives.

Stratified random sampling is a probabilistic sampling method, in which the first step is to split the population into strata, i.e. sections or segments.

In Grady et al (2008) the study examines the views of research participants in a hypothetical HIV vaccine study.  In particular, it examines views regarding individual compensation for participation and post-trial benefits to the community in which the trial took place. Here, the total population is stratified according to region – peri-urban, rural, and deep rural.

Infrared wavelengthrange in micrometers

No infrared is capable of reaching the muscle layers. In the subcutaneous tissue heat transfer is via conduction or diffusion, convection of heated fluids, blood etc, not by direct radiant heating and therefore more naturally favours processes that encourage absorption.

“Infrared Heating” is commonly understood to be Shortwave or Middlewave Infrared, here we have a basic infrared wave analysis.  Tungsten Halogen or Quartz lamps that emit red light are popular in outdoor heating and large public spaces. Construction industry professionals and others are aware there are different categories of infrared, but unaware that the differences are important when matching a heater type to the correct function.

The shorter the emitter wavelength, the larger proportion of energy is emitted in those shorter wavelengths (i.e. they peak earlier).

Grady, C. et al.  (2008)  “Research Benefits for Hypothetical HIV Vaccine Trials: The Views of Ugandans in the Rakai District.” IRB: Ethics and Human Research 30 (2): 1-7

The infrared waves in longer wavelengths assist considerably with absorption and low reflection – two essential properties of heating material. Conversely, Infrared-A is neither absorbed well and is highly reflected.

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What isinfraredused for

Infrared B and C (medium & far infrared) are the only infrared waves that transmit into the skin’s surface micro-region and are more highly absorbed into water and the blood than Infrared A making more effective onward conduction into the body fluids and conduction through the tissue and blood.

Infrared – A is classified as the ‘hottest’ infrared with temperatures up to 2,700C and wavelengths of 0.7 – 1.4 microns and is also called “Short-wave” or “Near” Infrared.

Transmission: When infrared is converted to heat in the transmitting region, this depends on the thickness of the target and how much infrared transmits. Transmission is not absorption, it is heat passing through and this is very important to understand – especially for Comfort Heating. High transmission implies low absorption and vice versa (high absorption = low transmission).

Heaters emitting IR-A , Short wave, will still heat and still emit Far infrared, but at lower densities than heaters optimised for Far Infrared output and consequently will be less efficient, whilst consuming more energy.

Natures in-built defence mechanism against high temperatures allows the skin to reflect a large percentage of shortwave energy and prevents its effective absorption. However Shortwave is still very transmissive (i.e. it penetrates deep into the skin). Academic research (citations below) recommends skin and eye protection from very hot short wavelengths. Shortwave is therefore not suitable for Comfort Heating.

The infrared wave analysis will explain why far infrared is the future for heating specific internal environments. For example; homes, offices and restaurants. However, exclude large space areas such as; factories, garages, warehouses, workshops where short & medium wave is more effective.

The graph shows the spectral output of lamps emitting within each of these 3 wavelengths. All the lamps have an output of different wavelengths and in different intensities.

Infrared wavelengthin meters

The graph illustrates that a large proportion of IR-A (Shortwave) will be reflected and not cause heating. This is a defence mechanism of the skin, to protect it from damaging ‘hot’ shortwave energy waves.

Far Infrared is biologically more significant in comfort heating than shorter (hotter) heat wavelengths because the skin has an 80% water content. Water absorbs heat wavelengths from 3 microns and above (Far Infrared). Far Infrared is better absorbed by the skin than other wavelengths; it is less “transmissive” and is not reflected – this is not so for shorter wavelengths.

Infrared – B is infrared with temperatures of 500 – 800C and wavelengths of 1.4 – 3 microns and are also called ‘Middlewave’ or ‘Medium’ Infrared.

Absorption: When infrared is absorbed it is converted into lasting heat in the target object. High absorption with low transmission properties means the direct radiant heat itself may not penetrate very deeply into the target material, but it can be transmitted onwards by conduction within the material (by the blood and other tissues in the case of skin). As the skin is 80% water, for Comfort heating and gentle drying purposes, we want an emitter lamp/ heater optimised to output in the wavelengths best absorbed by water (Robinson, 2014), which reflects the least, and for which transmission is possible by conduction or other means.

Prolonged IR-A exposure can cause eye damage. Goggles and time limits are recommended by Dr Janet Voke in Radiation effects on the eye, Part 1 – Infrared radiation effects on ocular tissue, Optometry Today, May 1999.

Microwavewavelengthrange

Hotter heaters do not mean more comfortable, but it does mean the use of more energy. Quartz heaters may be “hotter” at 3 microns than Far Infrared heaters, but the intensity of the heat is more suitable to industrial drying applications, sending heat long distances, and combating the effects of the outdoors – therefore not Comfort Heating. Far infrared creates Comfort Heating whilst consuming less energy.

These wavelength groupings are important to understand as they cover very different temperatures. They range from light-emitting (appears as a red glow) to non-light emitting (no glare or dark). The wavelengths have very specific properties in terms of heat absorption, transmission and reflection by the materials they touch.

Our Heat My Space infrared wave analysis compares short and medium waves with far infrared, to demonstrate why far infrared creates what is known as ‘Comfort Heating’ – that is – the comfortable heating of people or animals where skin contact is desirable.

This graph demonstrates that transmission into the skin is a function of wavelength. Infrared A/Short wave due to its lower absorption is the most highly transmissive into the skin.

Far Infrared emits the most biologically significant Comfort Heating wavelengths because skin content is 80% water which only absorbs heat wavelengths from 3 microns and lower (Far Infrared). Far Infrared is, therefore, better absorbed by the skin, less transmissive and less reflected. Academic research (citations below) recommends skin and eye protection from very hot short wavelengths.

Infrared wavelength chartnasa

As Infrared A is more transmissive in both the skin and eyes it overcomes the natural high reflectivity of the skin which is a defence mechanism. Installers and Operators of shortwave infrared must bear in mind the high temperatures of Infrared A and consider the exposure time and distance from the heater. Schroeder and others indicate Infrared A as being as harmful as UV light in terms of its ageing effects (Schroeder P, Calles C, Krutmann J. Prevention of infrared-A radiation mediated detrimental effects in human skin. Skin Therapy Letters. 2009 Jun; 14(5):4-5.)

Infraredfrequency range

“Preferred wavelengths for Comfort Heating“. Dr Gerard McGranaghan. Peter Schroeder, Judith Haendeler, Jean Krutmann, The role of near-infrared radiation in photo ageing of the skin, Experimental Gerontology, Volume 43, Issue 7, July 2008, Pages 629-632, ISSN 0531- 5565, Soyun Cho, Mi Hee Shin, Yeon Kyung Kim, Jo-Eun Seo, Young-Mee Lee, Chi-Hyun Park and Jin Ho Chung, Effects of Infrared Radiation and Heat on Human Skin Ageing in vivo, Journal of Investigative Dermatology Symposium Proceedings (2009) 14, 15–19; Schroeder P, Calles C, Krutmann J. Prevention of infrared-A radiation mediated detrimental effects in human skin. Skin Therapy Letters. 2009 Jun; 14(5):4-5. Dr Janet Voke, Radiation effects on the eye, Part 1 – Infrared radiation effects on ocular tissue, Optometry Today, May 1999.

Near-infraredwavelength

The graph shows, of the three infrared bands, water begins to absorb effectively at 3 microns (regardless of depth) and then again at 6 microns (for thin layers). Importantly this for the most part the Far Infrared region.

Module 11 of a course book by the International Development Research Center (IDRC), outlines the process involved in applying different sampling techniques in research.

For example, if interested in school achievement we may want to first split schools into rural, urban, and suburban as school achievement on average may be quite distinct between these regions. The second step is to take a simple random sample within each stratum. This way a randomised probabilistic sample is selected within each stratum. Each strata should be mutually exclusive (i.e. every element in the population can be assigned to only one stratum), and no population element can be excluded in the construction of strata.

Infrared wavelengthrange in nm

Stratified random sampling is used instead of simple random sampling when the categories of the strata are thought to be too distinct and too important to the research interest, and/or when investigators wish to oversample a particularly small group of interest. (Investigators oversample in the smaller strata in order to increase their sample size, which is necessary to conduct proper statistical analyses.) In practice, stratified random sampling along with other more complex sampling techniques are employed in large-scale surveys, especially governmental censes, to reduce some of the logistical costs associated with collecting information from a sample.

The skin has evolved to accommodate infrared in many ways to maximise (or reject) its various properties and the skin’s reaction depends on wavelength. The graph demonstrates the biologically significant reflection of Infrared-A/Short Wave by the skin. Reflection of the infrared heat is high in the short wavelengths and then decreases after 1.4 microns.

Infrared – C is infrared with temperatures of less than 500C and is the final and broadest waveband of 3 microns – 1mm and is also called ‘Longwave’ or Far Infrared.