- #1

OpenLaszlo

- 6

- 0

I'd to do a quick calculation to see what sort of power I would need to raise the temperature of a small sphere (1cm diameter, made of plastic or glass) with an absorption coefficient of about .5. I was thinking about using a bright LED flashlight (1200-2000 lumens) to do this. However, I'm having trouble computing how much energy I would be depositing on the sphere (I assume just the front surface). Essentially, I'd like to convert a certain exposure time (maybe 15s or so of illumination) into the units of Joules so I can roughly estimate the temperature change via Q=m*c_p*delta T.

I realize that the first step should be to convert lumens to candelas, which could be done if I can measure the beam angle of the flashlight. Once I have my number in candelas, however, I'm not really sure where to go. I've found a converter online at http://www.unitconversion.org/unit_converter/luminance.html which converts candela/m^2 to Watts/cm^2 per steradian (at 555nm). I'm unsure as to how they arrived at this conversion factor and was hoping someone might be able to lend a little insight.

Thanks!