Light distribution and candel to lumens conversion

[RusDyr]

Hi all.
Q1: Does anyone know which Ledil or Cutter optic for Cree XP-E/XP-G meet this requirements?



Q2: How to translate candelas requirements (there are it's "no less than 400cd and no more that 1200cd") to lumens? I don't understand at all which LEDs I should/could choose. :tired:

Appreciate you help!

 

[uk_caver]

For Q1, You probably want to start off with beam angle figures and plough through the datasheets.
From the chart you posted, looks like the 50%-of-maximum illumination level is around 15 degrees each way horizontally, and maybe 7.5 degrees vertically.

That's give a horizontal FWHM (full-width-half-maximum) angle of 30 degrees horizontally, 15 degrees vertically.

You're alreadly limited to looking at elliptical beam optics, which should narrow your search nicely, and if you're looking at XP-E/XP-G, you have the advantage of two different die sizes, so an optic that might give too narrow a beam with an XP-E might be close enough with an XP-G.

For Q2, some datasheets give figures for candelas-per-lumen for the beam centre.

For instance, with the Fraen FCP-E1-XPE1-0R elliptical optic, with an XP-G the FWHM figures are 13x44 degrees (possibly a bit wide for you?) and the on-axis intensity rating is 4.1candelas/lumen, so to get an 800cd peak central intensity, you'd ned to run the XP-G at ~200lm.

As to how a given optic performs for you requirements other than by having roughly the right FWHM figures, that's something I wouldn't like to guess

 

[HarryN]

There are many firms that offer optics, including Ledil, and also many other LEDs on the market in addition to Cree.

Most likely you can find a similar pattern by looking at Cree, Lumileds, and Osram offerings, and their related optics.

As UK_Caver noted, obviously the beam is elliptical, so that helps narrow it down. Step 2 is digging through data sheets.

Frankly, Step 3 is buying some and bench testing them. Ledil offers a kit of lenses for testing just for this reason.

If your beam pattern really "must" be like this, then you can always have an optic made.

 

[RusDyr]

Thanks!

I have read requirements throught more than twice, but found only this one:

7. INTENSITY OF LIGHT

7.1. The luminous intensity of the light emitted by each lamp shall not be less
than 400 cd in the axis of reference.

7.2. Outside the reference axis and within the angular fields defined in the arrangement
diagram in Annex 7 to this Regulation, the intensity of the light emitted by each
lamp must:

7.2.1. In each direction corresponding to the points in the table of standard light
distribution reproduced in Annex 3 to this Regulation, be not less than the minimum
specified in paragraph 7.1. above, multiplied by the percentage specified in the said
table of the direction in question, and

7.2.2. not exceed 1,200 cd in any direction the lamp is visible.

May be you'll be more lucky - it's from European regulation "UN ECE №87 UNIFORM PROVISIONS CONCERNING THE APPROVAL OF DAYTIME RUNNING LAMPS FOR POWER-DRIVEN VEHICLES"

uk_caver, how do you find out "candelas/lumen"? By estimate or anywhere from specification? I have tried to find it in Ledil optics specification but unsuccesfully. :(

 

[uk_caver]

uk_caver, how do you find out "candelas/lumen"? By estimate or anywhere from specification? I have tried to find it in Ledil optics specification but unsuccesfully. :(

http://www.cutter.com.au/proddetail.php?prod=cut960
click on link 'datasheet'
look on page 3/8 "Optical Characteristics – On-Axis Intensity (candela/lumen)"

From the figures there, you could probably get a *rough* idea of likely candela/lumen figures for optics from elsewhere with similar beamshapes.

Carclo also seem to give Cd/lm figures in some of their datasheets.