Learned something new yesterday...

I have always used an app calculator for calculate resistor value for my leds. I set it to 20mA that is max value of the led and write in forward voltage and input voltage etc. and the value i get, i choose og the nearest.

Yesterday i needed to solder on an led that lights up when power is connected to the pcb. I wanted that led to be dimmed and thought i just could doble the resistor value and try. No vissible change in light.

I must go to 20K resistor before it was dimmed enough(!!). That is around 0.9mA. This is an Blue 3mm led.

What i learned?

Use an 220 ohm resistor as an random resistor and the led will be bright enough.

I often use resistors up in k-range for leds. I think I had one down to 5-6mA and was still pretty fierce.

"Bright" is what the human eye and brain perceive as bright in a given situation. Our eyes/brain are highly sensitive and adaptable, you only have to try to take good photographs in dim light to appreceiate that. And modern LEDs are ever more efficient. So you have to consider how an indicator led will appear in different conditions. What looks bright enough indoors on a dim day will be hard to see at all outdoors in bright sunlight. That's why the dashboard lights in your car automatically adapt.

blomcrestlight:
I often use resistors up in k-range for leds. I think I had one down to 5-6mA and was still pretty fierce.

I was a little chocked when i could use 20k resistor for dimming an blue 3.3v 20mA led enough. My math (calculator) told me that the lled jst got 90uA and the light was wery dimmed but noticable. Enough for a indication inside a box. :slight_smile:

PaulRB:
"Bright" is what the human eye and brain perceive as bright in a given situation. Our eyes/brain are highly sensitive and adaptable, you only have to try to take good photographs in dim light to appreceiate that. And modern LEDs are ever more efficient. So you have to consider how an indicator led will appear in different conditions. What looks bright enough indoors on a dim day will be hard to see at all outdoors in bright sunlight. That's why the dashboard lights in your car automatically adapt.

True :slight_smile:

Working with the various Arduinox and modules, while the "pilot" light on many of them my be initially useful to demonstrate you have the power correctly connected, thereafter the light becomes an irritating nuisance!

Black Pentel pen!

its a good way to burn off some power!

Paul__B:
Working with the various Arduinox and modules, while the "pilot" light on many of them my be initially useful to demonstrate you have the power correctly connected, thereafter the light becomes an irritating nuisance!

Black Pentel pen!

I have some HDMI gear near my main TV that seems to have a 10W Blue LED with no series resistor. (Hyperbole intended). You could not watch the TV with this blue spotlight pointing at you. Being too lazy to open it and fix it properly, I just stuck a piece of Gaff tape over it. It was so bright that even with the Gaff tape over the LED, I could still see it.

aluminum insulation tape works great... i have it over my computer power light which pulses when it's in sleep mode.

Human (and animal!) vision has a logarithmic response to brightness, subjectively "half as bright" is actually more like 10 times less bright, measured in photons. Sound perception is similar. This why we can function
both at night, indoors, and in bright sun, there being several orders of magnitude difference in light intensity
between each environment.

What we can sense fairly sensitively is changes in brightness on a boundary between two areas, such as two
different kinds of paper side-by-side may be discernable as different, though you'd never see it if they weren't
side-by-side. Vision is much more sensitive to differences than absolutes.

MarkT:
Vision is much more sensitive to differences than absolutes.

More correctly, it is sensitive to boundaries or edges.

If the areas are not adjacent, it is nowhere near as easy. Note all the standard illusions.

Hi,
The OP has found why these LED module are able to be used for 5V and 3.3V systems and still remain basically the same brightness, they make protoboard prototyping so much easier.
Available in COM GND and COM V+.


Tom.. :slight_smile:

102 is only 100 Ohms… it could be much higher value and still annoying bright.

wolframore:
102 is only 100 Ohms... it could be much higher value and still annoying bright.

is'nt 102= 1k?

1=1, 0=0, 2=00?

1000 = 1k?

Oops you’re right... 1k

100 = 10 (this one looks strange)
10R = 10
101 = 100

TomGeorge:
The OP has found why these LED module are able to be used for 5V and 3.3V systems and still remain basically the same brightness, they make protoboard prototyping so much easier.
Available in COM GND and COM V+.


Tom.. :slight_smile:

You didn't give a link for that module!

(Just bought one for fun!)

you mean like this? I think I got the idea from larryd's cool posts... I made it so it plugs into breadboard rail on one side. no wire needed.