Physical Lights

Photographer Physical Lights add several Photometric and Artistic units that you would find in other softwares. Lights intensities is a broad subject that requires a bit of reading to grasps all intricacies of the physics behind visible wavelengths and the perceived brightness of light.

Here is a quick summary of the different available units in Photographer:

• Power (Watts): Cycles default Energy of a light source, it is a radiometric unit that does not take into consideration how the human eye perceives light.
  It is NOT the wattage information you find on lightbulbs packaging.
  The Luminous Efficacy is hardcoded to 683 lm/W. More information about Luminous Efficacy right below.

• Advanced Power (Watts): Similar to Power, but with exposed Luminous Efficacy. Luminous Efficacy defines the visible amount of light in lumen, generated by 1 Watt of energy.
  The default of 683 lm/W is an industry-standard representing the efficacy of an ideal monochromatic light source.

• Lumen: Luminous flux, photometric unit assuming a maximum possible luminous efficacy of 683 lm/W.
  It should be Normalized by Color Luminance in order to take into account the Luminous Efficiency Function that describes the perceived brightness based on the wavelength of a light source.
  Best for Point lights as this unit does not take into account the angle of the light. Lightbulb packages values can be used as reference.

• Candela: Luminous intensity (luminous power per unit solid angle), photometric unit assuming a maximum possible luminous efficacy of 683 lm/W.
  It should be normalized by Color Luminance.

Best for Spot lights to maintain brighness when changing the Cone Angle.

For Area Lights:

• Candela per Square Meter (Nits): Luminance unit which allows to maintain brighness of an area light when changing its size.
  Best for TVs and Monitors that use Nits to describe their pixel brightness.

• Lumen per Square Meter: While not a scientifically documented unit, this is often used for LED strip lights. It corresponds to the Emission intensity of the Area light surface and should not be mistaken for Illuminance in Lux.