Page 56 - Lasers and IPLs in Medical/Aesthetic Applications v1.2
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Chapter 1 – Fundamentals of Medical/Aesthetic Lasers and IPLs v1.2
Power & Power Density
● Power is the rate at which energy is delivered. In other words, it is the energy delivered over the pulse duration and is measured in watts (expressed as a capital ‘W’). One watt is one joule per second:
● So, a light bulb rated at 60 watts will emit 60 joules of light energy every second. Likewise, a 1 kilowatt (or 1 kW) electric fire will emit 1000 watts of radiative energy every second – in this case the energy will be seen as light (usually orange/red in colour) and felt as heat (which is infra-red energy) - Watch this interesting video.
● Power is probably the most important laser/IPL parameter after wavelength. This is simply because it is the power which determines the tissue reaction. If the power is too high or too low then the desired reaction will most likely not occur in the desired way.
● How the power is delivered is also very important. A high energy beam of light delivered over a long time may result in too much thermal damage in tissue. But, the same high energy beam delivered in a very short time may induce the perfect response, as in tattoo removal.
● Similarly, a low energy beam delivered over a long time period may stimulate a low level tissue response, as with LED systems and skin rejuvenation.
● So, the correct choice of power is critical in achieving the desired response in tissue.
 1 watt = 1 joule / 1 second
  Power – Lasers and IPLs
The power output from lasers and IPLs can vary enormously. In particular, we need to be aware of the difference between ‘peak power’ and ‘average power’.
Many lasers and IPLs emit a train of short duration pulses. Each pulse has a certain energy and the peak power is simply this energy divided by the pulse duration, ‘t’. Therefore, a train of pulses may have a peak power of 100 watts – that is, each individual pulse generates 100 watts of power.
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Chapter 1 LEVEL A Fundamentals of Lasers/IPLs
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