SJLD Dec 4, 2009:

symbols Φ are all meant to be diameter symbols not phis, and obviously referring to linear dimensions, not angles.
The diameter symbol is what I meant when I wrongly called it "theta".
http://schools-wikipedia.org/wp/d/Diameter.htm

FX Fraipont (X) Dec 4, 2009:

plenty of φ, for LED spot lights "MA347101 LED DIFFUSE ILLUMINATOR
The product features excellence of low power consumption, low heat, long service life, small size and adjustable brightness. It has 48 LED bulbs with four switches to control 8 LED areas for choosing different illumination angles.

◇ Power Supply: AC 100V-240V, 50/60Hz
◇ Maximum Power Consumption: 5W
◇ Output: DC 24V
◇ Brightness Range: 0-100%
◇ Dimensions: the top mount Φ(outer)78mm×Φ(inner)60mm; The top caliber of light flux Φ40mm; The bottom mount Φ(outer)123mm×Φ(inner)92mm"
http://www.viewsolutionsinc.com/products/LED Light.htm

SJLD Dec 4, 2009:

OK I got my Greek mixed up but anyway, beam spread would be fine if 110 was an angle (110 degrees) - but how likely is that for an LED?

FX Fraipont (X) Dec 4, 2009:

ϕ is not θ... otherwise it would be θ ...
This is beginning to look like a Magritte equation...

"A vehicle headlight, having multiple LEDs provided on a carrier and organized into a group arrangement having an asymmetric design arrived at by starting with an overall symmetric design and providing therein at least one area with non-functional or missing LEDs; and at least one optical element functioning as a common collection lens, wherein the vertical angle of beam spread φ is less than 5° and the horizontal angle of beam spread φ is in the range of less than 20° relative to the central optical axis of the optical element."
http://www.freepatentsonline.com/7534020.html

beam spread φ, anyone?

SJLD Dec 4, 2009:

I think maybe the symbol is meant to be a theta, signifying diameter - so the diameter of the field of the LED light is 110 mm at a distance of 400 mm???

FX Fraipont (X) Dec 4, 2009:

ϕ angle zénithal? ϕ est l'angle non orienté formé par les vecteurs z et OP, appelé angle zénithal ou colatitude Ce serait plausible : "field size" = un angle X 400 mm...

http://fr.wikipedia.org/wiki/Coordonnées_sphériques