Do LEDs refresh like fluorescents?
- Thread starter stdreb27
- Start date
scsinet
Active Member
I saw your PM as well, I'll just respond here...
LEDs only conduct (emit light) in one direction. In the case of an LED being fed by 60hz AC, they will flicker some.
In a 60hz application, the direction of the current changes direction 60 times per second, so the current is only flowing in any one of the two directions for (30) 1/30th of second periods every second. (I hope that makes sense, couldn't think of a better way to write it).
So an LED driven by AC is on every other 1/30th of a second, for 1/30th of a second. Or, to put it another way, it's on half the time and off half the time. Most people don't notice unless they are looking closely - but that's when an LED is used as an indicator... you only need to glance to see if an indicator is lit or not.
WHen you light something up with an LED - use it to cast light - such as with a moonlamp or an LED aquarium lighting system - it's easily perceptible.
Incidentally, incandescent lamps are the same way, but the nature of the filament means it is not perceptible. LEDS respond much faster, like fluorescent tubes, so you see it.
Most of the time, LEDs are driven by a wall adapter linear power supply, which usually incorporates rectification to send out DC, in which case an LED will not flicker. Or, they are powered by a switching power supply which, is almost always rectified to DC. Some switching supplies designed to run lighting are not rectified, such as the ones that drive those undercounter halogen lights, etc. Those, like electronic fluorescent ballasts, put out very high frequency AC, in the order of 45Khz or so, so the flicker is so fast that it is not perceptible, but very fast moving objects can "strobe" in the light, such as fan blade turning, as most of us have seen.
LEDs only conduct (emit light) in one direction. In the case of an LED being fed by 60hz AC, they will flicker some.
In a 60hz application, the direction of the current changes direction 60 times per second, so the current is only flowing in any one of the two directions for (30) 1/30th of second periods every second. (I hope that makes sense, couldn't think of a better way to write it).
So an LED driven by AC is on every other 1/30th of a second, for 1/30th of a second. Or, to put it another way, it's on half the time and off half the time. Most people don't notice unless they are looking closely - but that's when an LED is used as an indicator... you only need to glance to see if an indicator is lit or not.
WHen you light something up with an LED - use it to cast light - such as with a moonlamp or an LED aquarium lighting system - it's easily perceptible.
Incidentally, incandescent lamps are the same way, but the nature of the filament means it is not perceptible. LEDS respond much faster, like fluorescent tubes, so you see it.
Most of the time, LEDs are driven by a wall adapter linear power supply, which usually incorporates rectification to send out DC, in which case an LED will not flicker. Or, they are powered by a switching power supply which, is almost always rectified to DC. Some switching supplies designed to run lighting are not rectified, such as the ones that drive those undercounter halogen lights, etc. Those, like electronic fluorescent ballasts, put out very high frequency AC, in the order of 45Khz or so, so the flicker is so fast that it is not perceptible, but very fast moving objects can "strobe" in the light, such as fan blade turning, as most of us have seen.
stdreb27
Active Member
Originally Posted by SCSInet
http:///forum/post/2962055
I saw your PM as well, I'll just respond here...
LEDs only conduct (emit light) in one direction. In the case of an LED being fed by 60hz AC, they will flicker some.
In a 60hz application, the direction of the current changes direction 60 times per second, so the current is only flowing in any one of the two directions for (30) 1/30th of second periods every second. (I hope that makes sense, couldn't think of a better way to write it).
So an LED driven by AC is on every other 1/30th of a second, for 1/30th of a second. Or, to put it another way, it's on half the time and off half the time. Most people don't notice unless they are looking closely - but that's when an LED is used as an indicator... you only need to glance to see if an indicator is lit or not.
WHen you light something up with an LED - use it to cast light - such as with a moonlamp or an LED aquarium lighting system - it's easily perceptible.
Incidentally, incandescent lamps are the same way, but the nature of the filament means it is not perceptible. LEDS respond much faster, like fluorescent tubes, so you see it.
Most of the time, LEDs are driven by a wall adapter linear power supply, which usually incorporates rectification to send out DC, in which case an LED will not flicker. Or, they are powered by a switching power supply which, is almost always rectified to DC. Some switching supplies designed to run lighting are not rectified, such as the ones that drive those undercounter halogen lights, etc. Those, like electronic fluorescent ballasts, put out very high frequency AC, in the order of 45Khz or so, so the flicker is so fast that it is not perceptible, but very fast moving objects can "strobe" in the light, such as fan blade turning, as most of us have seen.
That is how I thought it worked. But wasn't sure. And I was just about to ask about DC current too.
http:///forum/post/2962055
I saw your PM as well, I'll just respond here...
LEDs only conduct (emit light) in one direction. In the case of an LED being fed by 60hz AC, they will flicker some.
In a 60hz application, the direction of the current changes direction 60 times per second, so the current is only flowing in any one of the two directions for (30) 1/30th of second periods every second. (I hope that makes sense, couldn't think of a better way to write it).
So an LED driven by AC is on every other 1/30th of a second, for 1/30th of a second. Or, to put it another way, it's on half the time and off half the time. Most people don't notice unless they are looking closely - but that's when an LED is used as an indicator... you only need to glance to see if an indicator is lit or not.
WHen you light something up with an LED - use it to cast light - such as with a moonlamp or an LED aquarium lighting system - it's easily perceptible.
Incidentally, incandescent lamps are the same way, but the nature of the filament means it is not perceptible. LEDS respond much faster, like fluorescent tubes, so you see it.
Most of the time, LEDs are driven by a wall adapter linear power supply, which usually incorporates rectification to send out DC, in which case an LED will not flicker. Or, they are powered by a switching power supply which, is almost always rectified to DC. Some switching supplies designed to run lighting are not rectified, such as the ones that drive those undercounter halogen lights, etc. Those, like electronic fluorescent ballasts, put out very high frequency AC, in the order of 45Khz or so, so the flicker is so fast that it is not perceptible, but very fast moving objects can "strobe" in the light, such as fan blade turning, as most of us have seen.
That is how I thought it worked. But wasn't sure. And I was just about to ask about DC current too.