A question about photometry and the photometric light

[odederell]

Hello all,

My name is Oded Erell and I'm a 3d rendering & Visualization Instructor.

 

I've aske the same question in the Autodesk area forum, and it's being ignored there,

So I think maybe it's more suited to this forum.

 

I have a question about pohotometric lighting units and the photometric light in 3ds max:

 

If I understand the definition of the Lux unit correctly,

an illuminance of 300 lux on a 1 square meter surface,

should be produced by a lamp focusing 300 lumens (idealy) exactly onto the surface.

 

And in an exactly 1 sterdian of a 1m radius sphere sector,

The different units should unite,

That is if a perfect lamp is at the center of the unit sphere,

and as a beem spread of exactly 1 sterdian,

it will light exactly 1 square meter of surface.

So if I am not mistaken about the definition of the photometric units,

In that ideal case,

the amount of CD would be equal to the amount of Lumens output and also equal to the amount of Lux illumination resulting on the surface.

 

I made a check using the photometric light in 3ds max,

And I got a different value in lumens.

In an approximately perfect sterdian and 1 meter distance lighting 1 square meter.

The photometric light converts 227 Lumens to 300 cd and to 300 lux.

I expected it to be 300 Lumens.

(rendering results are consistant, there is no actual change in the light intensity)

 

Am I misunderstanding the photometric units conversion?

Is there another explanation?

Any Ideas?

 

I've added a screen capture of the test.

 

Thanks for any reply,

Cheers,

Oded

 

[Ismael]

http://www.shoptronica.com/images/Calculo%20Candela-Lux-Lumen.htm

[odederell]

Thanks Ismael!

 

Problem not solved, but understood.

When we click a different input types of photometric units in the light's interface,

It will not show the correct numbers, but it will render correctly.

If you than type in the correct number, lighting wont change.

So unfortunately the photometric light can't be used as a calculator.