Ransen's Lighting And Color Blog

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. ...

There are in fact 6 types from I to VS/V Q. If the luminaire is not rotationally symmetric (V) or quadrilaterally symmetric (VS/VQ) t hen the following meth od i s used to find out which of I t o IV is the luminaire classification. Classification of Type I to Type IV is based on the extents of isocandle diagrams traced on the surface beneath the luminaire. In fact it just considers only the 50% of maximum isocandle path.  Look at the diagram below: Note that I said isocandle and not isolux . So we project the intensities (not the illumination) onto the road surface to make the diagram. The road and sidewalk together are divided into a grid of 16 rectangles based on the multiples of the mounting height (often abbreviated to MH ). A luminaire will have a distribution (Short, Medium, Long or Very Long) and a type (Type I to Type IV).  Here are the steps for finding out these distribution and type. Loc...