I appreciate that. Some standard assumptions are not standard to others. We use 3/4” or if I have to 5/8” garden hoses even though some of the old faucets we have here aren’t capable of full potential. Besides, when running garden irrigation off the demand 220v pump some of the standard assumptions don’t apply.
I’m mostly a stats guy, a favorite line a friend uses is a boy and his dog have 3 legs each. A simple view might be that they are both male and the dog is missing two legs . . it’s a wrong view.
My ax to grind on this is the discourtesy in the discussion. If NZ Shooter’s example was a wrong assumption relative to the flashlight science, THAT should have been the discussion - which is NOT achieved by using a simple argument. It’s a lot more appropriate to explain when the assumption behind the example can be valid, and then why that assumption doesn’t apply to the flashlight example. Too few seemed to be arguing the wrong thing because they don’t know the flashlight science and that is when we should stay out of that discussion or approach it with a lot more courtesy than many who should be walking are running and gunning.
@GottaZoom: When you put your finger on the hose to make the jet smaller, less water flows. No matter what preconditions you assume, thats the case. Unless you have a pump that is set to a fixed amount of water and therefore increases the pressure. But what would that pump do if you closed the hose? Make your pipes burst?
"A boy and his dog have 3 legs each." Whats that meant to tell us? I can interpret so many senseless stuff into that sentence, so whats the point?
Hammertime! No, flow is a combination of pressure and capacity. Reducing capacity increases pressure but that is only a flow reduction when the capacity drops far enough that the existing system pressure cannot rise enough to maintain flow. At that point increased pump pressure would be needed to maintain flow or the volume then drops.
That’s the point . . is a stat and so it will be interpreted wrongly. Doesn’t stop people from thinking they know something when they hear a stat, though. Think of it as a variation on the blind men and the elephant story. Or thinking that finding an answer on the internet is learning the answer. A sensible person will recognize they need more info to form a more complete picture, and then courteously ask questions so they might learn something.
I think everyone is tired of reading the useless runaway arguements from the past week. Lets all agree to keep it flashlights with a show of respect to NZ . innuendos and remarks should be where they belong, history. Those that showed up after some of recent fireworks looking for easy targets now that some of the dust has cleared with off the cuff slick remarcks, STFU..please
I was quite busy lately (I moved) and so I missed all the fun... (and fortunately the nasty parts, too.)
I still feel like adding some remarks... (an optics related thread without me? No way ^_^ )
Be careful with analogies: Do a water hose and a flashlight really have that much in common? Try obstructing part of the beam - does the light come out at higher speed or throw farther? (There's some fun though: Cut out a disc of cardboard about 2/3-3/4 of the flashlight's aperture's diameter and use some removable glue to fix it in the center of the front lens, compare with&without ^_^ )
Use proper terminology: A big part of this discussion was caused by misunderstanding each other. That's the reason why terminology was invented - to make sure everyone is talking about the same. ("Brightness" btw is not that well defined... Earlier it was defined as luminance, nowadays it's recommended to use it for subjective, non-quantitative perception. I think it's safe to say that this fresnel mod gives a brighter spot. It might even be valid to say that the little experiment I supposed above might give a brighter spot, though I'd find that quite confusing to say ^_^ )
I’ll try to help here. Feel free to step in GottaZoom. Simply stated, the issue arises when the hose id is larger than the supply. When that is the case pressure in the hose is LESS than pressure in the supply pipe. Therefore the pressure in the hose can rise when you put your finger over it until it hits the same pressure as the supply. Up until that point flow stays the same due to the pressure rise in the hose. It is after this point that the flow actually falls.
My science tells me the increase water velocity will make up for the decrease in flow area, i.e. flow rate stays the same. Common sense tells me when you adjust the faucet it takes longer to fill up containers. So I went out to the garage and open the faucet about half-way. Counted how long a small bucket filled up water coming out of the hose unhindered(took about 10 seconds). Emptied the same bucket and filled it up again but this time I partially blocked the end of the hose (about 75% blocked) and it took about 10 seconds also for the bucket to fill. I guess my results means I’m going to side with GottaZoom and NZShooter on the flow debate.
i’m glad you can chime in on the subject Drjones… maybe now we can put this all corrective term of brightness behind and move on the original purpose of this little experiment… which is just an IDEA.
an idea that maybe can be use to further more testing and creation to brighter lights without spending a lot of money in the future
In electrical circuits, one can emulate a constant current source by having a high voltage power supply in series with a high resistor. For example a 300 volt source in series with a 300 ohm resistor will give 1 amp to a 1 ohm load. It will also give 1 amp to a 2 ohm, or 3 ohm load. In other words, it would appear to be a constant current source.
This water and hose example appears to be a constant flow source because the relatively high resistance of the length of garden hose. Within certain changes in the restrictions at the end it can appear as a constant flow source.
In the above electrical circuit, placing a higher resistance load it becomes apparent the the supply is NOT a constant current source. (a 600 ohm load will only draw 1/3 amp)
Our pump doesn’t care whether faucets are open or closed. It runs by timer because it is for irrigation and always has a form of pressure relief, regardless of whether the 2 garden hose faucets are open or closed. Thus it never has fixed pressure level, (unless I gate off the irrigation and close all of the faucets, in which case a pressure relief valve will open and hold pressure to protect the pump). Our system is more of a constant flow system, actually somewhat similar to the professors assumption (though we can tune for varying power, pressure, and thus output). Pumps generally won’t pump pressures greater than the system if it was built well. Generally a relief system is designed in (especially when built by someone smarter than me) to protect the pump and system. The primary risks in our system are a waste of energy and pump life.
Funny thing is you helped come to that conclusion by not opening the faucet all the way. Depending on other factors it might be different. It’s that complexity that keeps me asking questions.
While we practically cannot speed up light, most of us aren’t measuring speed. We’re observing volume in full or in part. Blocking the beam by redirection to change the locally observed volume is exactly the point of the thread. Sometimes an analogy is useful, if not exact.
Quality isn’t the best because it’s a soft (flexible) lens and I just moved it with my hands. I left ambient light on to reduce brightness adjustments in my camera (compact camera, no manual settings)
However you see that it is indeed similar to a zoom light as there’s a position where LED and reflector are projected onto the wall. Near that position however there’s a position where that image is blurred into a quite good and quite bright spot.
Fresnel lenses are quite lossy, quite dome of the light is scattered at the edges. A real lens of same size would give a better performance, pot probably some more artifacts, too. Main contribution to throw is lens size and quality.
A high quality aspheric lens with same area and with a (bare) LED in it’s focus will have the best throw, but a smaller spot.
yeah, that was the base of my experiment, now i’m trying to move into adding combination of different lenses to see if i can manipulate lights into thrower or floodier ( for bike light)
i want to buil something like light device but in smaller scale
maybe you can give me some input on these experiement, i found a success hooking my Trustfire WF 502B into telescope and it able to throw as far as 300’+, but the hotspot starting to dissappear and turn into a doughnut … but it still reach
now… if i can somewhat miniaturize this device using combination of telescope optics ( which i have plenty of) that will be great