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Old 19th September 2020, 08:35 AM
Richard Richard is offline
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Join Date: Dec 2005
Location: Notts
Posts: 5,073
Default LED Indicator Resistor Calculator

LEDs are a current device and are often supplied by an over-voltage supply which is current-limited by a series resistor.

The most important value we use to set the brightness and not over-run the LED is the amount of current we want the LED to pass.

There are newer LED versions on the market such Super Bright and Ultra Bright but of the ones I've tried these just allow greater current, and hence brightness, and behave quite similarly to Standard Bright at lower currents.

For an indicator, a Standard Bright Diffused is more evenly lit at low levels. A Super Bright can be run low and tends to emit a point souce light at lowest levels which can look good depending on what you want. I avoid Clear LEDs for this job as they can dazzle and really only look good at higher light levels.

Of the popular colours Green and Blue appear brighter than Red at lower current levels.

The simplest thing I can say is you'll find a setting of 3mA - 5mA will be good for a panel indicator using a 3mm or 5mm Standard Diffused Green or Blue LED. For a Red indicator you may need double that current for a similar visual level.

The general Max for these LEDs is around 20mA so start there if you like and wind it down but the eye adjusts for low light levels so don't be surprised how low you end up setting it.

There's a formula for working out the current manually but this calculator is vastly quicker and lets you input options and adjustments instantly,


https://ledcalculator.net/#p=50&v=2&c=4&n=1&o=w


I've left the default setting at the one I've just installed which is a Standard Green 5mm power indicator run off the amp's 50V rail. Have fun
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