Understanding polar curves of luminous intensity

Confounded by polar displays of light intensity for Type C photometry? Try this!

[Monty-Goodman]

After 12 years, it still helping. Thanks for this video!!!!

[Amber-W]

I've spent few hours trying to understand how to read Photometic Diagram but still do not understand what written in the website, then I try youtube and found your video which helps me to understand in few minutes.

Thank you very much

[spektrograf]

Thank you so much for this video. I've been studying Cuttle's text on lighting design and hit the section on spatial illumination distribution which made little sense to me until I watched your video. Now the chapter just snapped into focus. Thank you!! 👍

Thank you for your intuitive and informative explanation.

[iesdallas]

Your link is a MOST helpful example of Lighting Analysts' enduring commitment to serve / help / enable our lighting community.  -   Paul Coppage,

[lightinganalysts]

The term Horizontal was selected (i believe, it's been used in the industry for decades) as the base of the cone is projected onto a horizontal plane to be viewed in two dimensions (the red line).

[TrentMRobertson]

It would be nice to have a quick explanation on the polar graph on the different numbers and what they represent. Also, what illuminance level the colored lines represent. I think the shape is intuitive, but how that translates to a real building with real equipment is what I find confusing.

[Melanie-gpmk]

Could you please explain the relationship between the angles and the shape of the vertical plane of light? I see that as you go from 0 + 180 degrees to 30 + 210 degrees and so forth the shape gets wider, but I do not understand how these angles are determined. Basically, when looking at the shape of the light, how can I determine what the angle is?

[Lumenez]

It's honestly very easy to grasp. If you just try to imagine for example a 2x4 with a frosted lens on a type C goniophotometer you would get more rounded distribution, where as if you have a linear prismatic lens on a vapor tight for example it would look more jagged. It is really just about looking at the light distribution in real life and imagining it on a 3D plot. As for polar plots, they give you 0-180 and 90-270 so just understanding where the axis are and how the fixture is mounted in reference to that is a big help

[Bushwack]

Why do I not see a "horizontal" cone? To me, a cone that's horizontal would have its base plane perpedicular to a traditional XY plane, with it's point pointing either in the plus or minus X direction. I.E., if you were holding a little wooden cone "horizonatally" in your hand, you'd have the point facing to the left or right. In this video I see no such visual metaphor.

[lightinganalysts]

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