Understanding VH lighting photometric diagrams

VH lighting diagrams are cartesian (compare with polar diagrams). They are normally used for floodlights. They show a "hemisphere of intensities", it is assumed that no light is projected out backwards. In the real world "out backwards" would be towards the sky or the spectators of a football match.

The V and H angles are explained graphically here:


And here is an example:


In the icon top left the flat side of the hemisphere is the one which emits light.
The diagram above will be easier to understand if you also look at this annotated photometric solid:




Just to explain a bit more, imagine this luminaire is at the end of a playing field, above the goal, and imagine it is pointing into the center of the field:




As the V angle increases you are pointing further and further away from the goal, and closer to the center of the field. You could imagine that
  • V=-30° points directly at the goal
  • V=0 points at the center of the field
  • V=+30° points at the opposite goal. 
V is the Vertical angle. H is the horizontal angle and points to the left and right of the line between the two goals.

(In practice of course it is rare to have a floodlight above the goal, but it helps us to imagine what V and H mean.)

And here is one more graphical explanation of VH diagrams


(For an explanation of what intensity, luminance, and illuminance means, this book...

http://www.ransen.com/photometric/Candelas-Lumens-And-Lux.htm
 
  ...will help you)

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