Logically, using a smaller diameter light curing tip should increase the irradiance of an LCU. In reality when measured, an LCU unit with a smaller tip diameter will generate a nearly 5x decreased irradiance reading on a radiometer.
What am I missing?
Dear Ahmed Abyad ,
to my opinion, the total amount Io of light picked up by an optical fiber (or light guiding rod) is proportional to the fiber cross section, which is proportional to the square of the radius und thus proportional to the square of its diameter Do: Io ~ Do². So for any other fiber/tip diameter D the total amount of light I behaves like: I/Io = D²/Do², when all other parameters (geometrical and optical) remain unchanged. For D < Do we also have D² < Do² and from that: D²/Do² < 1. Thus I = Io*D²/Do² < Io.
When D is decreased, why should it be logical to have an increase of radiometer reading, as you stated above?
Dear Gerhard Martens
The radiometer reading should increase because irradiance is inversely proportional to the surface area the light source is projected on to.
Your answer though clarifies the issue, the fiber optic rod picks up less light to begin with causing the decrease in irradiance.
Thank you for the answer
Dear Ahmed Abyad ,
thanks for feed back.
Under the constraint, that all light emerging from the tip is picked up by the radiometer, the radiometer reading is proportional to this amount of light. For a preset amount of light there is no dependence on the light emerging area.
The irradiance is the amount of light picked up by the radiometer divided by the net area of the radiometer, but not divided by the area of light source or fiber tip cross section.
- Badges
- Science topic