Power density represents the actual Laser/LED incident power in watts on the tissue and the spot size area (output power divided by irradiated area), while energy density represents the therapeutic dose incident on target tissue and represents the product of output power and exposure time, divided by irradiated area.
There is a confusion in using radiometric terms in both professional and commercial literature. "Power density " is simply irradiance W/sq.m (or Illuminance lux/sq.m)
"energy density" is a wrong and confusing term. In fact it is defined as "Radiation Exposure (H) and measured in W-sec. Be aware that these two quantities are not necessarily linearly related (Bunsen Roscoe) by their biological effect.
Dear Benzion... Is interesting your exposure about these terms. I never have read in these terms yet, but I found it very elucidated. Thank you
Hi Rodolfo. Glad to be helpfull. BTW in the past I served as one of the editors of CIE international Vocabulary of radiometric terms. There is a great mess among life scientists and even optical and lighting engineers about using correct standard terms. A propos, energy density is simply lux (lm/sq.m) and not lux/sq.m as I wrote
Dear Benzion, if we have a LED light that is diverging, because it has more LEDs, hiw do I know the area irradiated? Or I should chose this in my clinical study? Because I see in all calculations (I need to provide beam spot size at target, radiant exposure, radiant energy and total radiant energy) I should know the size of area irradiated. I own a power meter and the light. For me as a clinician it is difficult to cope with these parameters. Thank you.
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