In carpentry, we’d say that the pro would make his mistakes look like they were meant to be that way.
Minor nitpick… [:D] LEDS can be dimmed just like bulbs.
I use LEDs almost exclusively on my special effects light boards and fire engine installs and do all kinds of dimming, flickering, etc.
For example, I have an old fashioned tower beacon that ramps up from off to full on and dims the same way. I use the same effect for a lighthouse, only I keep the LED dimmed between “flares.” Another mimics the old fashioned “bubblegum” police lights.
I use a programmable chip to do the different effects and use LEDs because of their longevity. They’ll outlast most of us. [;)]
Mike Tennent
Semi-true. An LED really can’t be dimmed in the same manner as a light bulb. Once you reach the forward voltage threshold, the LED will conduct and light. They really don’t get brighter with more voltage. You CAN control brightness a bit with current, but there’s only a relatively narrow range that this works without letting the magic LED illuminating smoke out.
What you CAN do is vary the duty cycle of the LED so it APPEARS to be dimmer or brighter. Some decoders can do a decent job of this, some can’t.
–Randy
Well…
May I suggest a short experiment?
Take 2 AA batteries (3 V DC), a common T1 LED, and a 1K potentiometer. Assemble in the usual manner so that the pot varies the resistance to the T1 LED.
What you have is a nice little adjustable dimmer for LEDs. You’ll have a smooth linear progression from off to full intensity, merely by adjusting the pot.
I tried it with a variety of LEDs I had on hand. Works like a charm (as I knew it would.) I’m not claiming it’ll work with any combination of LED, voltage, and pot. The voltage and the sensitivity of the pot will make a big difference.
But the above does demonstrate that you can indeed dim an LED in the same manner you can dim a bulb.
Mike Tennent
The light output of an LED is directly dependant on the current flowing through an LED.
More current = more light. Less current = less light.
LED’s have an “almost” fixed voltage drop, which varies a little depending on their temerature and the current flowing through them. If you want the complex equation to calculate the actual voltage drop across a diode I can get it for you. For all intents and purposes we call it 0.6 volts. The current flowing through one of our LED’s is calculated from the following equation:
Current = (supply voltage -0.6 volts) / dropping resistor value in Ohms
The resistor value is dependant on the maximum design value for the current flowing through the LED. This is typically around 0.020 or 0.030 amps (20 - 30 miliamps). This CAN be much higher or lower than that, depending on the LED.
Some LED’s are actually constructed internally with multiple LED’s in series. 2 LED’s would give you 1.2 volts of drop, 3 would give you 1.8 volts of drop, etc. The big advantage of this is that MOST of the power is consumed by the dropping resistor, and by stacking LED’s in series you can double or triple the light output and consume very little or no extra power.
DCC can serve and LED by being a current source, and not being a voltage source, so no dropping resistor may be required.
Mark in Utah