Explanation of Energy Terms
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.