NOTE: Converting between geometry-based measurement units is difficult and should only be attempted when it is impossible to measure in the actual desired units. You must be aware of what each measurement geometry implicitly assumes before conversion. Any results with this converter must be considered approximate.
STEP 1: Enter the ORIGINAL measurement taken in W/m2 or W/cm2 with your light meter and sensor here. This number can be entered in decimal format (i.e. "0.000341") or in scientific notation (i.e. "3.41e-04"). Select what units - W/m2 or W/cm2 the measurement was taken in.
STEP 2: Enter the MEASUREMENT DISTANCE at which the reading in Step 1 was taken, in this box. This number can be entered in decimal format (i.e. "0.000341") or in scientific notation (i.e. "3.41e-04"). Select whether the distance is in meters or in feet. If you are measuring in units less than meters or feet (i.e. millimeters or inches) you will have to convert these numbers up to meters or feet first.
STEP 3: Enter the SHADOW DEGREES (solid angle) in the numerical stepper here. This is the solid-angle of light that is occluded or blocked by the lamp base.This angle can be any number between 0 (perfectly isotropic source) to 120 degrees. This can be a difficult property of a light source to measure, which is a contributing factor for why any conversions done with this calculator are to be considered approximate and should only be used as a last resort when measuring watts in an integrating sphere is not possible. In many cases, the default of 30 degrees is sufficient for the expected accuracy of this conversion process.
OUTPUT: This is the APPROXIMATE TOTAL WATT OUTPUT of the lamp. Again, this calculator makes several assumptions which directly affect the accuracy of the conversion. Since this is a measurement geometry conversion - this cannot be helped. This calculator assumes that the light source is a point-source and is isotropic (output is the same in all directions) in nature with the exception of the losses due to the lamp base which are again, assumed, to be about 30 degrees solid-angle. The lamp is also assumed to have a clear envelope. Variances from these assumptions will lead to additional error in the conversion process and could invalidate any results (i.e. in the case of trying to convert an illuminance reading from an area source).