John_A_Pham@cup.portal.com (06/05/90)
Can someone tell me what is the average time for a LED to fully lit and vice-versa? I remember it is around 3Khz or was it 300Khz? John
rpw3@rigden.wpd.sgi.com (Rob Warnock) (06/05/90)
In article <30513@cup.portal.com> John_A_Pham@cup.portal.com writes: +--------------- | Can someone tell me what is the average time for a LED to fully lit | and vice-versa? I remember it is around 3Khz or was it 300Khz? +--------------- It depends on the LED, but more on the driving ciruits. I have driven the red LEDs in H-P low-cost plastic fiber-optic cables at 10 MHz and above. The 1300nm LEDs in FDDI controllers run at 125 megabaud (100 Mb/s of 4/5 coding). Even dirt cheap LEDs can be run at several megahertz. Of course, good luck trying to build a dirt cheap *detector*... ;-} -Rob ----- Rob Warnock, MS-9U/510 rpw3@sgi.com rpw3@pei.com Silicon Graphics, Inc. (415)335-1673 Protocol Engines, Inc. 2011 N. Shoreline Blvd. Mountain View, CA 94039-7311
John_A_Pham@cup.portal.com (06/06/90)
In article <61580@sgi.sgi.com> rpw3@rigden.wpd.sgi.com (rob warnock) writes: --In article <30513@cup.portal.com> John_A_Pham@cup.portal.com writes: --+--------------- --| Can someone tell me what is the average time for a LED to fully lit --| and vice-versa? I remember it is around 3Khz or was it 300Khz? --+--------------- -- --It depends on the LED, but more on the driving ciruits. I have driven --the red LEDs in H-P low-cost plastic fiber-optic cables at 10 MHz and --above. The 1300nm LEDs in FDDI controllers run at 125 megabaud (100 Mb/s --of 4/5 coding). Even dirt cheap LEDs can be run at several megahertz. -- --Of course, good luck trying to build a dirt cheap *detector*... ;-} Ooops, I should make that clearer. I want the refresh rate for LED that a human eyes can tell between an OFF and ON cycle. Heck, for 1mhz or faster, LED will just fully lit to the human eyes John
dt@yenta.alb.nm.us (David B. Thomas) (06/06/90)
John_A_Pham@cup.portal.com writes: >1mhz or faster, LED will just fully lit to the human eyes whew! no kidding. Fluorescent tubes turn on and off at 60 Hz (with 60 Hz power applied, as in the us), and I can just barely keep up with them, myself! David Thomas dt@yenta.alb.nm.us
berryh@udel.edu (John Berryhill) (06/06/90)
In article <30550@cup.portal.com> John_A_Pham@cup.portal.com writes: > > Ooops, I should make that clearer. I want the refresh rate for LED >that a human eyes can tell between an OFF and ON cycle. Heck, for >1mhz or faster, LED will just fully lit to the human eyes Although the persistence of visual images depends upon intensity and color, 15 Hz is generally the point where you can't quite tell whether an LED is on steadily or flashing. -- John Berryhill 143 King William, Newark DE 19711
grege@gold.GVG.TEK.COM (Greg Ebert) (06/06/90)
>--+--------------- >--| Can someone tell me what is the average time for a LED to fully lit >--| and vice-versa? I remember it is around 3Khz or was it 300Khz? >--+--------------- >-- > > Ooops, I should make that clearer. I want the refresh rate for LED >that a human eyes can tell between an OFF and ON cycle. Heck, for >1mhz or faster, LED will just fully lit to the human eyes I used 100Hz, but you can go down to 50Hz. Watch the duty cycle vs. current - at lower duty cycles you need to increase the current to obtain the same luminous output. I built a multiplexed 10-digit display, thus each digit has a 10% duty cycle. I got decent brightness at 2.5ma/segment at DC, so I ran 25ma/segment during multiplex operation. By the way, when I say '100Hz' refresh rate with 10 digits, I am switching at 10*100Hz = 1Kz.
jbm@eos.UUCP (Jeffrey Mulligan) (06/08/90)
berryh@udel.edu (John Berryhill) writes: >In article <30550@cup.portal.com> John_A_Pham@cup.portal.com writes: >> >> Ooops, I should make that clearer. I want the refresh rate for LED >>that a human eyes can tell between an OFF and ON cycle. Heck, for >>1mhz or faster, LED will just fully lit to the human eyes >Although the persistence of visual images depends upon intensity and >color, 15 Hz is generally the point where you can't quite tell whether >an LED is on steadily or flashing. I would say more like 50 or 60 Hz. This is why TV uses interlace: although a 30 Hz frame rate is acceptable for sampling motion, 30 Hz flicker is unacceptable, so by displaying the even lines and then the odd lines large areas have an effective flicker rate of 60 Hz. BTW a previous post on this topic incorrectly stated that flourescent lights flicker at 60 Hz; the flicker rate is 120 Hz since the lights glow during both + and - phases. -- Jeff Mulligan (jbm@eos.arc.nasa.gov) NASA/Ames Research Ctr., Mail Stop 262-2, Moffet Field CA, 94035 (415) 604-3745