Infrared Radiation (IRR) in Physiotherapy


Infrared irradiation (IRR) is electromagnetic energy invisible to the human eye, having a wavelength between 760nm to 1mm. In the electromagnetic spectrum, the infrared own the place between visible light and microwaves.

electromagnetic spectrum

It used for the relief of pain and stiffness and to enhance healing of soft tissue lesions and skin condition, by producing the superficial thermal effect in the tissues.

Production of IRR

Any hot body emits infrared ray; the sun, gas fires, coal fires, electric fires, hot water pipes, etc. for therapeutic purpose, IRR produced by two types of generators- the nonluminous and luminous generators.

Source of IRR Production

Non-luminous generators provide infrared rays only, while luminous generators emit visible and a few ultra-violet rays as well as infrared.

The spectral values of-

  • IRA vary from 760nm-1400nm.
  • IRB vary from 1400nm-3000nm
  • IRC vary from 3000nm-1mm

Types of Infrared Generators

There are two types of infrared generators-

  1. Luminous generators
  2. Nonluminous generators

1) Luminous generators-

Luminous generator for IRR

  • Rays emitted from the luminous generators
  • It is produced by one or more incandescent (Radiant) lamps.
  • An incandescent lamp consists of a wire filament enclosed in a glass bulb,  which may be evacuated or may contain an inert gas at low pressure.
  • A part of the inside of the glass bulb is often silvered to provide a reflector.
  • The filament is a coil of fine wire and is usually made of tungsten: as this material tolerates related heating and cooling.
  • The passage of an electric current through the filament produces heat, infrared red, ultraviolet, and visible radiation.
  • The ultraviolet produced is absorbed by the glass of the lamp, and therefore it’s not emitted.
  • These lamps generally available  with a power level of between 250-1500W
  • The lamp available at this time generally emits IRR, with wavelengths of between 780nm -1500nm with peak intensity at 1000nm.
  • Penetration→ the dermis and subcutaneous tissue to a depth of 5-10mm.
  • The luminous generator is sometimes called radiant heat.

2) Non-luminous generators

non luminous generator for IRR

  • These generators consist of a coiled resistance wire.
  • Which is looped around or fixed in a ceramics insulated material and produces far infrared electromagnetic rays (1500-12000nm)
  • Infrared radiation(IR) will be emitted, by both the wire and heated material surrounding it.
  • These generators produce only infrared radiation and no other visible radiation.
  • These are generally available with power levels of between 750-1000W.
  • The infrared emitter is placed at the focal point of a parabolic reflector, to reflect the radiation into an approximately uniform beam.
  • The reflector has on its front a wire mesh.
  • These generators produce radiation which peaks at a wavelength of around 4μm(4000nm) and penetrates the epidermis (2mm).

Though both the lamps require a warm-up period, non-luminous lamps take longer than luminous lamp to reach a peak level of heat emission, because of the thermal inertia of the considerable mass of metal and insulating material that has to be heated.

The small lamps may take 5 minutes, but larger ones may take up to 15 minutes to reach maximum emission.

Physical Effects of IRR

IRR obey the law of electromagnetic radiation such as:

  • Reflection
  • Refraction
  • Transmitted
  • Absorption

Like any other radiation, IR falling on the surface of the skin is partially reflected and partially absorbed through penetration.

For therapeutic infrared, the amount of reflection is negligible.

Lambert’s cosine law– close to 95% of the radiation applied perpendicular to the skin are absorbed,  through transmission into body tissue and only a small amount is reflected.

The transmitted energy is rapidly absorbed, so only a small amount of radiation penetrates the subcutaneous tissue and most of the energy is absorbed in the skin.

Physiological Effects of IRR

  • Cutaneous vasodilation
  • Increase sweating due to increase activity of sweat glands.
  • Sensation of warmth due to stimulation of thermal heat receptor
  • Increase in metabolism-  According to Vant Hoff’s law, the chemical changes are accelerated due to heat, the heat produced by infrared radiation increases the metabolism due to which there is increased demand in the tissue for oxygen and foodstuffs which is maintained by an increase arterial flow.
  • Nerve stimulation– Due to the effects of heating the thermal heat receptors in the skin are stimulated.

Therapeutic Effects and Uses of IRR

  • Pain relief
  • Reduction of muscle spasm
  • Joint stiffness
  • Edema relief
  • Skin lesion (psoriatic arthritis with psoriasis)
  • Dermal ulcers (pressure ulcers)

Techniques of Application

Choice of apparatus-

  • Choose the modality i.e. luminous or nonluminous.
    • For chronic inflammatory conditions where tissue heating is required, a luminous infrared lamp is selected.
    • For acute inflammation or recent injury  the sedative effect of the rays obtained from the non-luminous generators
  • Apparatus should be in working order
  • Pre-heated at least 5 minutes before heating.
  • Not the voltage of emitter.
  • Usually lamps with emitters from 250-1000 Walt are used.

Preparation of Patient-

  • The position of the patient should be comfortable and adequate.
  • Avoid undue movement of the patient.
  • The part to be treated should be exposed and the rest of the body should be covered.
  • Protect the eyes of the patient.
  • Test the skin sensation of the patient.
  • Remove all metal objects like rings, safety pin, etc.

Arrangement of lamp and patient-

  • Arrange the lamp so that the rays strike the skin at right angles.
  • The distance of the lamp from the patient should be measured, approximately 75-90cm for non-luminous and 45-60cm for a luminous lamp.
  • Set the timer.
  • For an acute condition, duration should be 10 to 15 minutes and for chronic conditions it should be 30 minutes.

Termination of treatment-

  • Following the cessation of treatment, the skin should feel mild to moderate warm to touch and there should be mild erythema.
  • A record should be kept for each treatment.

Dangers of IRR

  • Burn
  • Electric shock
  • Gangrene
  • Headache
  • Faintness
  • Injury to the edge.

Contraindication to IRR Treatment

  • Areas with defective cutaneous thermal sensation.
  • Areas with defective arterial blood supply.
  • Subjects with advanced cardiovascular disease.
  • Hemorrhage
  • Scar tissue or tissue devitalized by deep x-rays treatment or other ionizing radiations
  • Malignancy
  • Acute skin disease, e.g. dermatitis, eczema.
  • Superficial infections.


  • Electrotherapy Therapy Simplified – Basant Kumar Nanda