Light
is Energy
It
is easy to disbelieve that light is usable energy. We live among
so many devices that use radiant energy, that they have become
invisible. Radios receive radio frequency waves and translate
it into music (sound waves). Tvs receive high frequency waves,
either by air or through a cable. We cook our food with microwaves.
The list goes on. Not to mention the most important source, our
Sun.
 |
The
wavelength of light is measured in nm (nanometers). Visible
light extends from deep violet (~ 390 nm) to deep red (~ 750nm).
Smaller
wavelength light contains more energy than longer wavelength
light. |
How
big is a nanometer?
From
the name, we can imagine that it is very small. Most metric measurements
are divided into steps of 1000. A meter, is slightly smaller than
a yard. There are 100 centimeters (cm) in a meter (2.5 cm to an
inch). There are 1000 millimeters (mm), 1,000,000 micrometers
(um) and 1,000,000,000 (a billion) nanometers (nm) to a meter.
So the measurements of wavelength used to describe visible light
are quite small.
What
are the energy measurements for LED light
The
amount of energy deposited on a surface is measured as Watts.
It is made more comparable by specifying the Watts in a unit of
area.
For LED light, the common units of phototherapy are mWatt/cm2.
(There are 1000 mWatts in a Watt).
The
effect of energy deposited on a surface also depends on the amount
of time, is known as power, measured in Joules. The measurement
of power at a surface is a Joule, defined as a Watt deposited
in one second for a defined area.
In
phototherapy the effective range is 1 – 30 Joules/cm2.
Spectral
Power vs. Total Power - which is important?
 |
While
most manufacturers offer their specifications in total
power output, Dermillume devices are tested for
spectral power output.
Total
power output includes the large amount of waste heat that
is created by energizing the LEDs. Usually ¾ of total
power is wasted as heat.
It
is the spectral power (the light) that makes changes in
the skin. |
Loss
of Energy over Distance
Many manufacturers
list the energy emitted at the face of the device, rather than
at the surface of the skin. It is important to know that the energy
declines as the inverse square of the distance (1/d2),
which is an exponential lessening of strength.
This means
that at 4.5 inches from the surface, the spectral energy intensity
has decreased 130-fold!
Therefore,
The Dermillume Pro1500 requires 2612 mWatt/cm2 blue
light at the device surface to yield 20 mWatts/cm2
to the skin surface.
Other
Topics: [LED vs Laser][Precision
Light Therapy]
