How is laser output measured?

Energy and Power

Energy is measured in Joules, A joule is the amount of energy exerted by a force of one newton to move an object one meter.

Power is measured in Watts and is the rate of energy delievered

ie. 1 Joule in 1 second = 1 Watt

Average Power and Peak Power

Peak Power is the maximum power during a pulse

Average Power is the amount of energy per second = pulse energy x repetition rate.

Spot Size and Treatment Area

The diameter of the laser beam used on the patient’s skin. Measured in millimetres

In most cases it is better to talk in terms of a treatment area as a 5mm spot size covers only 0.2cm² (A=?r²).  IPLs mostly use rectangular guides ie. 1cm x 5cm = 5cm² treatment area ie. 25 times bigger than a 5mm spot size.

Fluence or Energy Density

Fluence = Energy/ Area   J/cm²

If the spot size is increased the fluence is deceased.

If 15J is delievered in a spot size of 5mm (treatment area of 0.2cm²) the fluence is:-

15/0.2 = 75 J/cm²