Beam Angles

Kitchen Panda

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I'm having a hard time interpreting beam shots. It seems to me that beam angle would be a good thing to know, and would give a numerical distinction between "throwy" and "floody" lights. Just to clarify the question in my mind, I tried some lights, estimated the diameter of the "hot spot" and calculated beam angles.

LightDistance InchesSpot Diameter InchesBeam Angle Degrees
Ikea Jamso LED desk light293257.8
#222 Penlight 2AA301222.6
Photon Micro Light 5 mm LED301120.8
Illuminati CA1-AL319.517.4
Battery Junction Keychain30917.1
Quark AA80.631712.0
Pelican L1 5 mm LED3059.5
Led Lenser 3AAA304.58.6
TK70365325.0
Mag LED 3D (tight)364233.6
2 for $6 Canadian Tire 2D incandescent884.52.9
Craftsman Laser Distance Measure3680.130.019



It's hard to estimate the hot spot size since I was eyeballing it; I should have picked the 10% of peak brightness contour, or something like that, to make it a scientific measure.

So, I would expect anything with a hot spot beam angle of much less than 10 degrees would be called a "throwy" light, and wider beam angles would be "flood". (The Maxabeam Web site shows what a 1 degree beam angle would look like.) The desk lamp is handy...it's hot spot is only a little more than one steradian, and it has almost no spill, so now I have a reference for what a steradian looks like.

The incandescent lights I have are very poor, but represent a lot of really crummy flashlights. The beam angle is probably not quite as tight as I report it because the little orange spot these make is hardly even circular. The #222 penlight is the oldest flashlight I own; it must be 40+ years old, and has consumed innumerable batteries and bulbs over that time.

The keychain button cell LEDs have no reflectors; it's just the LED dome concentrating the light. The Craftsman laser was what I was using to measure distance and then I thought "It's a light, isn't it?" Not very many lumens, but very throwy. What's 3 millwatts of red light in lumens?

The Mag-Lite was turned down to its narrowest beam; set on flood, the "donut" was taller than the wall I was aiming at 30 feet away. The TK70 hot spot was very broad and could be larger than what I measured.

I wish more beam shots were taken against a grid.

Bill
 

StarHalo

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I've just gone by lux numbers all these years; anything 5000 or below will generally have a broad, floody beam that makes for a good EDC/around the house light. 10,000 and above is the land of throwers.
 

Bolster

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Hi there. I mostly hang out in the headlamp forum. For us headlampers, advertisers will start to call something "flood" as narrow as 30 degrees, but a true flood IMHO is 60-120 degrees. 60 is close to the SF Minimus. The floody Zebralights are around 80. Spark's SD52 is 115...now that's a flood!

I also have the issue of finding where to measure to, and from. I generally look for the point at which the light falloff approximates 50%.

I agree that the hot spot's the thing to measure. I spot-checked your math and came up with the same numbers you did.
 
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kaichu dento

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It seems to me that beam angle would be a good thing to know, and would give a numerical distinction between "throwy" and "floody" lights.
I'm glad to see this thread as I've been wishing for quite some time that we could know not only the angle leaving the light of the hotspot, but the spill as well.
I have two favorite lights when it comes to spill angle and they are my E1e and E2e, the former being absolutely perfect thanks to the diffusion film that spreads the edges and softens them at the same time.

For hotspot and the Quark MiNi AA has the perfect hotspot and if I could I would develop a reflector that would match the hotspot of the MiNi AA with the spill of the E-series incandescents.

This would not be the best for some needing more throw, but it would be one of the most user friendly daily-usage beam patterns possible, lighting virtually everything within view, including peripheral vision. If someone beats me to it, let me know!
 

StarHalo

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For hotspot and the Quark MiNi AA has the perfect hotspot and if I could I would develop a reflector that would match the hotspot of the MiNi AA with the spill of the E-series incandescents.

The Xeno E03 XM-L has the same size hotspot as the Quark Mini AA, but with a much broader spill beam; makes for an awesome indoor/backyard use beam, and at the same price..
 

kaichu dento

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The Xeno E03 XM-L has the same size hotspot as the Quark Mini AA, but with a much broader spill beam; makes for an awesome indoor/backyard use beam, and at the same price..
Just sold two E03's, one of which was the XM-L version and I guess you've been doing this for long enough that you understand that just because you like one aspect of a lights design, doesn't necessarily make you want to keep it.

I'm happy with my compromise lights for the most part and look forward to emitter outputs rising to the point that I can have my dream beam pattern combining the spill of the E1e/E2e and hotspot of the MiNi.
 

Kitchen Panda

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Hi there. I mostly hang out in the headlamp forum. For us headlampers, advertisers will start to call something "flood" as narrow as 30 degrees, but a true flood IMHO is 60-120 degrees. 60 is close to the SF Minimus. The floody Zebralights are around 80. Spark's SD52 is 115...now that's a flood!

I also have the issue of finding where to measure to, and from. I generally look for the point at which the light falloff approximates 50%.

I agree that the hot spot's the thing to measure. I spot-checked your math and came up with the same numbers you did.

There's a UK Web site selling MR16 and similar bulbs with an interactive illustration of beam angle. The MR16 literature calls 24 degrees a "flood" but it's still a pretty concentrated beam by flashlight standards. I can see how a 120 degree flood is useful in a headlamp since a spot beam means you're constantly moving your head every time you move your hands; not too bad if you're pounding a tent stake or changing a tire, but undesirable if you're caving!

I was surprised that even a 2 for $6 flashlight has a very narrow beam angle, though I suppose it makes sense - to get any range out of the low-power bulb, you've got to squeeze it down. The spot it makes is kind of peanut-shaped, though.

Thanks for checking the math - I also found some on-line calculators so I could check my spreadsheet formula. While I was hacking around I found that candelas * beam angle squared divided by 4180 = lumens, for small angles (less than 60 degrees) - handy for mental arithmetic since I have a hard time doing arc tangent in my head. So, for a 2 degree beam angle, a "million candlepower" spotlight has to put 956 lumens inside the hotspot. I suspect the hottest part of the hot spot is a lot less than the overall beam angle.

Bill
 
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