NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: led lights
From: Ken James
Date: 2003 Nov 26, 17:13 -0600
From: Ken James
Date: 2003 Nov 26, 17:13 -0600
> The obvious question that comes to mind first is: "If the brain does not have > enough time to tell that the light is off, why does it have enough time to tell > it's on?" Quite right...the answer is the threshold of quanta. As long as you can cross it, then any added (within these paremeters) is just wasted. So the answer is that once you get the system to see the light as "on", you can shut it off for a very brief time and it will not notice the 'missing' light...as long as the parameters are correct. In other words, the argument could be reversed to explain why a > flickering LED should look darker than a continuous one, With the correct paremeters, flickering CAN make it look dimmer. But I don't want a dimmer light. BUT, if you turn it on for at least 100ms and then off for not more than 100ms (optimum), it will look almost as bright as if it were on the entire time...provided the other paremetrs of min peak intensity ect are also met. Then you can fool around with the different values to get different effects. . At any rate, I am not > convinced that the exploitation of this phenomenon makes any physical sense. Well, it has been used for quite some time...if you flick your eyes at leds, you will see that many are indeed pulsed. In fact ON semi conductor as well as several others mention it in their engineering application notes as a way to conserve battery power... > > 1) The trick works only as long as there is only one light source, or as long as > all light sources are driven by the same driver. Yes, to a large extent. Otherwise the intensity of > light would be averaged before it reaches the eye. This would seem to limit the > applicability. It is true it is not as noticable in illumination applications...I designed this driver mostly for visibility apps. However, it is also superior electrically in many respects, so although it is not my fiirst choice for large cabin lights (a DC-DC converter of very efficient design coupled with a control IC is my first choice for illumination with larger lights), for smaller bunks lights and task lights, it works very well, and for nav lights it is ideal. > 2) As you say yourself, the test person may well have the _impression_ that the > light is brighter, but that does by no means imply that he sees better. True...but there is some gain in these apps, just not as much. inventing the perpetuum mobile. The human eye is not liniar. So it is possible to take advantage of this a bit and not violate any physics! So, what is the advantage > of having a cabin light "LOOK" brighter? You won't be able to read better in > this kind of light. One advantage of the driver (besides 'brightness enhancement', which as I've already said is not the best app for this type of driver in illumination uses) is 'loss-less' dimming so you can have a task light only as bright as needed and not waste any power not needed at that time, and it also is a very efficient regulator, as the other thing I do with this driver as a regulating function is to trade off peak intensity for average intensity, within the previous parameters, so that the light stays almost at the same intensity from 10 vdc to 14.5vdc. It does this without wastiing any power, as it just adjusts pulse width as a function of voltage input. I might mention that all the lights will shut off the leds when the voltage is too high so as to protect them, and there is a tremendous amount of overvoltage and transient protection built into the circuit...it can easily handel anything it may be likely to encounter except a direct lightning hit. -Ken