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)

Comments

  1. UnknownSeptember 26, 2017 at 5:17 AM

    Superbly written article, if only all bloggers offered the same content as you, the internet would be a far better place..
    Pendant Lights

    ReplyDelete
  2. Baker AxtonDecember 19, 2017 at 9:35 PM

    This is the first time I came to this blog and I found some relevant stuff here. Basically I keen to know new parameters of writing every-time and sometime it become really very hard to find such kind of platform.หลอด ไฟ

    ReplyDelete
  3. Asim ShaikhJanuary 19, 2018 at 3:19 PM


    Your blog provided us with valuable information to work with. Each & every tips of your post are awesome. Thanks a lot for sharing. Keep blogging,
     Lampen

    ReplyDelete
    Replies
    1. Owen RansenJanuary 11, 2019 at 11:04 PM

      Glad to be of help. Also writing an explanation to myself helps me understand...

      Delete
  4. Billy.July 16, 2018 at 8:23 AM

    Remarkable and steady article.


    Accountants Hove

    ReplyDelete
  5. Hector62January 11, 2019 at 3:22 PM

    Excellent information. I leive in Colombia South America. How can I buy your book?

    ReplyDelete
    Replies
    1. Owen RansenJanuary 11, 2019 at 11:07 PM

      You can get it on Amazon or at LuLu.com , search for Ransen...

      Delete
  6. Henry WhiteJanuary 25, 2024 at 10:01 PM


    Super blog, really informative. Thank you

    gawler self storage
    gawler self storage truck hire

    ReplyDelete

Post a Comment

Popular posts from this blog

How to understand photometric polar diagrams

Image
If you are working in the lighting industry sooner or later you will come across photometric diagrams and you must know how to interpret them. This blog entry page is quick introduction on how to look at a photometric diagram and get important information from it. Often photometric diagrams use the C-Gamma system. Gamma=0 points downwards towards the floor or road. Gamma=180 points upwards to the ceiling or sky. Here is a C-Gamma diagram with some of the luminous intensity “rays of light” left in: The "rays" make the diagram more confusing than it needs to be and photometric diagrams always leave out those “rays” to give you a simpler diagram as shown below: The point to remember is that the distance from the center of the diagram to one of the points on the “outline” corresponds to a luminous intensity value, often in candelas, in the given direction. These diagrams
Read more

There are two sorts of Duv (Delta u v and Delta u' v') in lighting - what is the difference?

Image
Unfortunately there are two sorts of Duv, and they are both to do with the color of light sources, which makes it really confusing. Here they are: Duv on a CIE 1960 u-v chromaticity diagram: This measures how far away the color is away from the Plankian locus of black body radiation. It's assumed that this locus is natural light in at various times of day. So the closer the u-v coordinates of the light is to that locus the more "natural" and "high quality" the light is. D u'v' spatial chromatic nonuniformity: The other "Duv" is the spatial chromatic nonuniformity of a given light source. In English this means that Delta u' v' is a measure of how far the color of a light source varies at different angles. For example a LED light might be more blue in the horizontal gamma=90° direction than it is the the vertical gamma=0° direction. Here's an invented example: The colors have been exaggerated but you can see that at gamm
Read more

How to calculate Beam Angle, Field Angle and Nema class

Image
In floodlight VH (large area) photometries the field angle is the opening in degrees at 10% of the maximum intensity. The beam angle is the opening in degrees width at 50% of the maximum intensity. So the field angle is wider than the beam angle, it requires less intensity. As a mnemonic remember that a field (of corn for example) is much bigger than a beam of wood (in a barn on the same farm). Well. Hey. That is how I remember it! Here is an example (from OxyTech's PhotoView program):  Here's a graphical explanation of where those numbers come from (screenshots taken from OxyTech's photometric program PhotoView): In the above image the calculation for beam and field angles for H (=horizontal) has been made explicit (blue arrowed lines). See if you can roughly confirm the beam and field angles for V (in red) from the photometric polar diagram.
Read more