Can anyone explain the link between the light intensity units?

[Jpjapers]

In the intensity drop down when using a corona light you can set what units you want to use.
Are these correct conversions when changing the units?

[mferster]

Not really because the conversion doesn't take into account the angle/spread of the light into its conversion equation.

Here's some reading

https://www.compuphase.com/electronics/candela_lumen.htm

[Jpjapers]

Not really because the conversion doesn't take into account the angle/spread of the light into its conversion equation.

Here's some reading

https://www.compuphase.com/electronics/candela_lumen.htm

Thanks, This is why i wish we had a corona light meter like the mental ray one. Being able to measure lux at floor level and then replicate it in Max would be so useful!
It would be nice to find the time to build some properly set up lights that just work as they should eventually.

[houska]

In the intensity drop down when using a corona light you can set what units you want to use.
Are these correct conversions when changing the units?

Actually, yes, these conversions are correct, but they only take into account the limited data that can be inferred without doing any super-complicated and lengthy calculations.

In particular, if I recall correctly, they calculate with the light object's surface volume, they presume lambertian light emission distribution and they assume that the light has a wavelength of 555nm, where the light sensitivity of human light sensitive cells is the highest.

[houska]

And if you'd like me to be more specific, the formulas are following:

[Lumens] = [watts/(sr*m²)] * radioToPhoto * π * SurfaceArea
[Candelas] = [watts/(sr*m²)] * radioToPhoto * SurfaceArea
[Lux] = [watts/(sr*m²)] * radioToPhoto * π

Radio to photo is a conversion factor between radiometric and photometric units (this is where the 555 nm are taken into account)

[Jpjapers]

This is a very interesting answer, thanks for sharing!
So is there a physically correct way to set up a light for accurate emission based on the datasheet of a light fitting? Would you need to make a corona light that is the size of a bulb filament?

[houska]

So is there a physically correct way to set up a light for accurate emission based on the datasheet of a light fitting? Would you need to make a corona light that is the size of a bulb filament?

I'd say your best bet is probably using a light with .ies profile. Modelling a bulb filament doesn't make much sense unless you're planning to do shots very close up.

[Jpjapers]

<SNIP>

I'd say your best bet is probably using a light with .ies profile. Modelling a bulb filament doesn't make much sense unless you're planning to do shots very close up.

Ahh I thought as much. Thanks for the insight!