Power
Power and energy are closely related. Power is the rate at which energy is delivered, not an amount of energy itself.
Formula:
Power = Energy / Time 1 Watt = 1 Joule / Second
Terapeutic Energy = Power (Watts) or Joules/sec x Time (sec).
Power Density
Power density or Irradiance refers to the amount of power delivered per unit area.
Power density indicates the degree of concentration of the laser output
It is expressed in Watts per square centimeter (W/cm2), or miliWatts per square centimeter (mW/cm2)
Some studies have concluded that the power density may be of even greater signifcance than the dose.
Example: A laser’s output is 4 Watts, and it is illuminating a circle of 3 centimeter diameter.
First fnd the area of the circle, 3.14 x 1.5 x 1.5 = 7 cm2.
Then divide the power by the area, 4W / 7cm2 = 0.6 W/cm2.
Formula: Irradiance (PD) = W/cm2
Energy Density(ED) / (Fluence)
The energy density expresses the total amount of energy delivered per unit area, in Joules per square centimeter (J/cm2).
Te energy is measured in Joules, and is calculated by multiplying the power output of the laser times the amount of time elapsed during the laser treatment.
Example: A 4 Watt continuous wave laser would deliver 240 Joules in one minute. (4 Watts x 60 seconds = 240 Joules) Ten simply divide the total energy by the area to arrive at the energy density in Joules per centimeter squared.
Formula: Fluence (ED) = Power x Exposure Time, measured in Joules/cm2 (Watts x Seconds)
key:The amount of energy delivered, determines the magnitude of the laser interaction within the tissues and the individual cells
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donna@gigaalaser.com
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