|
|
|
| Authored by: myNym on Wednesday, October 17 2012 @ 03:19 AM EDT |
I had an LED calculator. With its display set to all 8s
"8.888888888 88" (representing 8.888888888 x 10^88) it drew
over half an amp. Killed 9V batteries fast.
The typical LED of the day was designed to emit full
brightness at 20mA, DC. LEDs are more efficient today, and
2mA rated LEDs can be found.
Current limiting was used to hold the current at the LED's
rated current. If you wanted to dim the LED, you pulsed it.
I was an Electronic Engineer in early 80s. I designed
circuits that used LEDs back then. The need to pulse LEDs
to control the "brightness"* was known widely.
* I put brightness in quotes, as it is only the perceived
brightness that changes. The LED operates at full
brightness during each of the pulses. As long as the LED is
pulsed fast enough, humans will not see the flicker. That
is why a 20KHz florescent light ballast is more pleasing to
the eye, especially when in the presence of motion. Try
waving your hand rapidly in front of your face while
illuminated by only a 60Hz ballast sourced florescent light.
You'll see the hand flicker. The effect won't be as
dramatic as when using a strobe light, as the florescence
doesn't fully decay to dark between pulses, and the
pulses are sinusoidal, not square waves.
[ Reply to This | Parent | # ]
|
|
|
|
|
