Conventional Fixtures S4 beam spread table

[TheTheaterGeek]

Is there something like this in ft/in?

https://html1-f.scribdassets.com/5c3v0t6qyolsxsf/images/1-66cdea0fd8.jpg

Just a table of beam spread data?

 

[Harley Morgan]

Here is a sheet I wrote up in excel a couple years back. Written in excel 2007. It includes just about every conventional fixture type I could think of at the time. This also contains photometric data, where available. It doesn't include any of the new LED lekos.

You can enter horizontal / vertical distance, or if you know the actual throw distance, that can be entered as well.

https://onedrive.live.com/redir?resid=653093200F7D5E60!3977&authkey=!AKnJ_mfwJjr2enk&ithint=file,xlsx

 

[sk8rsdad]

It's not a table but this handy calculator from ETC is pretty useful.
http://www.etcconnect.com/minisite/sourcefour/metrics.html

 

[derekleffew]

Here is a sheet I wrote up in excel a couple years back. ...

From the Calculations tab:

Multiplying Factor = (Degrees) x (.018)

Rather than

Beam diameter = distance * (2 * tan (beam angle in degrees / 2))

Somewhere on here I've written questioning what I call the "0.018 constant", both its original source and veracity.

Here's a similar spreadsheet:
http://www.derekleffew.com/Conv_Photometrics_v7.xls.zip?attredirects=0

 

[sk8rsdad]

The 0.018 is a rounding of the conversion of degrees to radians.

As we all know, a radian is the angle formed by an arc whose length is the same as the radius. Since the circumference of a circle is 2 pi times the radius, a semicircle is pi radians.

Since the angle of a semicircle also equals 180 degrees, 1 degree is equal to pi/180 radians.

pi/180 is approximately equal to 0.018

QED

 

[Les]

As we all know, a radian is the angle formed by an arc whose length is the same as the radius. Since the circumference of a circle is 2 pi times the radius, a semicircle is pi radians.

Yeah... Everybody knows that... ;-)


Thinking I probably shoulda listened better in geometry class.



Sent from my iPhone using Tapatalk

 

[woolycd]

The beam spread table uses a constant for any given beam angle [Beam Spread = 2 x Throw Distance x cos(φ/2)]. The dimension units show up on both sides of the equation so they divide (cancel) out. You use the same table for feet; just replace all references to meters with feet and it works. If your throw is outside the range of the table, use half the distance and multiply the spread by 2. It's more interesting to set up a spreadsheet for beams that are not normal (perpendicular) to the surface.

 

[derekleffew]

The 0.018 is a rounding of the conversion of degrees to radians.
...
pi/180 is approximately equal to 0.018

[not] QED

No matter how many digits I use for pi, I always come up with 0.017, following the 5/4 rounding rule. Am I missing something?

 

[sk8rsdad]

Am I missing something?

Why, yes! Yes you are. However, pendantry is definitely (or should I misuse defiantly as others are wont to do) not it.

 

[TheTheaterGeek]

The 0.018 is a rounding of the conversion of degrees to radians.
As we all know, a radian is the angle formed by an arc whose length is the same as the radius. Since the circumference of a circle is 2 pi times the radius, a semicircle is pi radians.

But of course........



Haha.

https://onedrive.live.com/redir?resid=653093200F7D5E60!3977&authkey=!AKnJ_mfwJjr2enk&ithint=file,xlsx

Thank you so much guys, this has helped a lot. I wish that ETC thing was in like an smartphone app.

I welcome more explanation on the math of the subject though. I am learning i think, though, i never thought i would see cos ever again. Had to look it up.

 

[TheTheaterGeek]

[Beam Spread = 2 x Throw Distance x cos(φ/2)].

What is this "φ" ?

 

[woolycd]

"φ" [phi] is a random Greek character I use to designate the an angle. In this case, the beam angle. I should know better than to not define all variables in an equation.

 

[TheTheaterGeek]

"φ" [phi] is a random Greek character I use to designate the an angle. In this case, the beam angle. I should know better than to not define all variables in an equation.

No its alright. I got it.

 

[woolycd]

Looks like I made another rooky mistake. The equation should be:

Beam Spread = 2 x Throw Distance x tan(φ/2)

You'll see the results look more like the ETC Beam Spread Table now. I don't get much chance to do any trig in my current job.