What's this ambient/diffused LED light "thing"?

What\'s this ambient/diffused LED light \"thing\"?

Every once in a while on the board I read of a referece to the issue of LED flashlights and ambient/diffused light, and it sounds like it something the poster doesn't like. Could someone give me a quick explanation of the phenomenon they're speaking of? Are they considering it a downside to LED's, a quirk, feature, side-effect? Thanks!!

Re: What\'s this ambient/diffused LED light \"thing\"?

According to dictionary.com:

dif·fuse
To pour out and cause to spread freely.
To spread about or scatter; disseminate.
To make less brilliant; soften.

I believe that diffuse is pretty much a synonym for the amount of side-spill an LED or light-assembly produces. For example the Inova X1 produces a near perfect circle of light, so it's beam is not diffused at all, but the Inova X5, on the other hand produces a wide beam with a 'hotspot' and lots of spread-out dimmer light (sidespill).

X1 Beamshot (Non-diffused beam):
Here-X1

X5 beamshot (Diffused beam):
Here-X5

Edit: Most people like a bit of sidespill/diffused light. When using a beam that has almost no sidespill, and trying to use it to walk somewhere, you have to constantly 'sweep' the ground with the light to see where you are going. With a nicely diffused beam, you can see both what is ahead of you (with the beam's brighter 'hotspot') and where you are going (with the less bright but very usefull sidespill).

Hope this helps,
-Brad

Re: What\'s this ambient/diffused LED light \"thing\"?

I may be barking up the wrong tree with this reply, but if so I'm sure someone else here will correct me.

The thing about (most) LED lights is that (without reflectors/optics, etc) they tend to provide an even "floodlight" effect when illuminating an area. This is sort of like having a garden hose set to spray. The practical result is that a much larger area gets covered, but any one spot gets less water (or light). So you may have a powerful light putting out 60 lumens total, but it is diffused enough to seem dimmer at any one point and so the light itself sometimes seems quite a bit dimmer overall.

This effect can be very desirable when you are doing close in work like setting up a campsite or trying to read a book because you CAN see an entire area all at the same time.

However this effect is far less desirable in SAR (Search and Rescue) or tactical type operations where you tend to want a more focused beam that concentrates that full 60 lumens in a tighter spotlight with more "throw" so you can aim the beam at specific objects further away and see them clearly, or jolt an agressive oponent.

Many of the new LED light designs tend to modify the beam (with reflectors, optics, etc) into something closer to tradational incandescent lights. A hotter center with some "throw" and a good "side spill" to illuminate an area. The balance between the two isn't alway well thought out though /ubbthreads/images/graemlins/ooo.gif.

Re: What\'s this ambient/diffused LED light \"thing\"?

The quick'n'dirty explanation is that LED light does not do well when used with ambient lighting; such as street lights. Its almost as if the LED light is actually ABSORBED by the incan/tungsten/etc. Like many folks who haven't seen it, I too thought the notion was silly; until I experienced it first hand in a dimly-lit back yard with bad guys in the area. My pretty new SF L4 with McGizmo two-speed tail cap simply would NOT penetrate the shadows beyond the spill of the incan street light back there, rendering it virtually useless. Fortunately, I had an issue Stinger in the car.

I have since seen the phenomena in numerous other settings. The are several other cops on this board who will tell you the same thing; for a "war light", incan is the way to go.

If you do not make a habit of going in harm's way, you will probably never be bothered by this. Just know that it is real, and can be a factor if you need to see beyond the pool of light cast by street lights, etc. A good hot incan is the ticket for that.

Re: What\'s this ambient/diffused LED light \"thing\"

There's nothing really mysterious at all regarding this issue with LED flashlights. The fact is that, until quite recently, LED lights were not available that focused their beams anywhere as tightly as the typical incandescent flashlight. For example, this throw chart shows that the Surefire L4 (22.64) has a considerably weaker hotspot than a Mini-Mag or cheapo Eveready 2-D incandescent (both 29.73). Almost all of the LED models that make 35+ on that chart have come out in the last year.

Some people have speculated that the spectrum difference between LEDs and incandescents makes the latter better in some contexts, which is probably true to some extent. (The human eye is more sensitive to yellowish light compared to bluish.) But unless you are comparing two flashlights that are roughly similar in hotspot brightness as measured by a light meter, then it's pretty much pointless to worry about tint. In the end, much higher lux values will stomp over other differences.

Re: What\'s this ambient/diffused LED light \"thing\"

Most LEDs in lights are not designed for 180-360 degree lighting but rather something more along the line of 20-45 degrees. A diffuser redirects the light and scatters more of it so the degree of light covered approaches an area light instead of a flooding spotlight.

Re: What\'s this ambient/diffused LED light \"thing\"

i would like to see what the OP was refering to in the context that it was used ??

but to continue the discussion, i will add some observations.
ya average HIGH-POWER Dome led, has about a 60*-120* as high as 180* output,

with a reflector on a normal dome light, only the stuff traveling to the reflector (about 20* and over) gets turned into whatever spotting, the reflector can accomplish. the rest of the light, the light that did NOT hit the reflector, spills out into a lower level round, of about 20*.
you often cannot SEE that in the beam pictures, there is a SPOT and a low level flood, when using a reflector on a DOMED led.
Reflectors with high-dome leds, seem to be the most efficient in what heads FOREWARD out of the light (lumens). they make a good spot, and can have a great flood around them. (best of both worlds, for walking light)

its easy to think of, when you realize the parts, you have a bulb that is 120* , and a reflective cone around it, there is a ammount of the light, that doesnt have to hit that reflective cone to get out.

With Side emitters, almost everything that hits the reflector, goes to the spot that the reflector is aligned for, there is very little Other light, that heads out the front that does not hit the reflector, because the top of the led is DESIGNED for 360* output.
so there is far less of the perefreal lighting , and mostly just a spot.
side emitters are not so efficient, yet there is far less perefreal light, and its mostly all just spot.
and because the side emitters output is a TIGHT 360 point, it makes a tight beam, depending on the reflector (of course).

With OPTICS, ALL of the light heads through the optics, even in a dome, so that is LOADS different, with optics most of the light becomes the spot, and there is Little of this "spill"
BUT
with most optics they are not very spotty, they are VERY well blended , and dont have nasty flashlight rings and donuts and blackholes.
They have optics in all kinds of angles and styles, from floods, lines , and spots as high as 6* , but some of the ratings for the degrees, is based on "from center" meaning a 20* could be 20x2 going each way from the center.
the 6* one is not much spottier than the 10* lux standard thing, i think there is limitations to this type of refraction, and still having smoothness.
optics have a reduce efficiency, and some of the light spills out the sides , and is lost in the light (doesnt go foreward) this can be reduced by reflectivity behind the optics, and should have been fixed by silvercoating the back of the optics.

sooo, basically unless you have the high-loss side emitter, you dont get a SPOT ONLY tight spot, that ONLY lands in ONE area. and untill it only lands in one area, your IRIS of your eye will be effected by the ambient or perefreal light.

and finally, there is a reflector with a 2* spot, it looks a lot like the thing on a surgeons head its a Spot reflector, its 2 inches and VERY flat. it will make a spot so tight that it blows away the spots in about anything.
i have yet to see it be applied in many thing, yet it would fit in a single lux mag.
there is 2 sizes of it, and its available on a non-english (US) site.
it makes a harsh but kinda nasty spot, of a side emmiter, or a dome.

then there is the super rediculously long reflectors that have harsh spots also, and very little light just spills out from the dome.

hope any of that helps, that is the way i see it, some of it you cant see in the pics, except for the pics where the person specifically showed it, by adjusting the camera.

anything else is just the fact that with 3W of luxeon, your not going to compete with 9-40watts of incadescent, but you might have a battery that still lights something after 2 hours
IMO you should have 1/2 the power of leds to gain the same output as high-efficiency ("zenon" or halogen) overdriven short lived bulbs, to have similar output. they are efficient, but not so efficient as to think that an underdriven 1W is going to compete with a 24W battery vaccume /ubbthreads/images/graemlins/smile.gif

Re: What\'s this ambient/diffused LED light \"thing\"

I'm the original poster. My question was really just out of a lack of knowledge of the phenomenen that you all have seemed to explain very well. I had seen numerous references to the above mentioned absorption/diffusion/"ambient light issue" of LED light in different threads on this forum and thought I would try to find out what exactly the people are talking about, or how it may effect a decision between an LED light and an incan light. My first high end LED was the L4, a week or so ago. I have often noticed that in dimly lit areas or brightly lit rooms that the L4's massive total amount of light can be less obviously "there", making the L4 seem like it might be a weaker light than we know it is. However, in a dark room or outdoors, that massive amount of overall light shows up big time as a big wall of light making the L4 a very useful light that needs almost no sweeping around or movement of the beam. That's a great and useful light in my opinion, but I can see how the yellower light of an incan can show up more, stand out more maybe you'd say, in the presence of other light in the room or outdoors area.

Re: What\'s this ambient/diffused LED light \"thing\"

Yup, the L4 is notorious around here as a "non-thrower," but it's still quite popular for close-range and medium-range tasks. And since it has an E-series Surefire body, you can spend a modest amount of additional money to add an E2e incandescent head or a KL1 LED head.

The newer KL1 is a much better thrower than the KL4 (the head that comes with the L4), but the KL1's sidespill and total light output are much less. It would give your L4 a lot more "reach" but at the expense of a narrow beam that might have to be swept from side to side in some situations.

Re: What\'s this ambient/diffused LED light \"thing\"

Here's my practical scenario illustration, albeit similar to Steve C's good example:

While out for a night walk, we approach an area where an irresponsible neighbor has been known (based upon prior Close Encounters) to allow his pit-bull to roam free. My path-illuminating SF KL1 and KL3 or Inova T2/T3 LEDs will NOT cut through the "ambient" light (from a corner street light) to several ominously-dark landscaped areas beyond that street light's puddle.

However, being a typical Knuckle-Dragging Paranoid Violence-Prone Anti-Common-Good Ugly American Neanderthal, I still need to know: is that dog out there... waiting for me, once again? I WANT to know this so I'm not taken by surprise by another Pearl Harbor sneak attack from close range by any 4-legged (or 2-legged) territorial/predatory critter. BT/DT.

My incans (Pelican M6 or SL Scorpion or Stinger, or MAG-charger) enable me to illuminate those black shadows 50-75 yards out there -- and find any surprises awaiting. The LED's -- while they generate pretty Beam Shots on an interior wall -- don't.

Same principle applies to dimly-lit parking lots -- a favorite grazing area for Socially-Disadvantaged Maladjusted Multiple-Tattooed Street Cretins soliciting involuntary contributions for financing their trendy Nocturnal Chemical-Recreation Funds. Incans + Colt 1911 .45s work well there. LEDs + Peace & Love medallions don't.