This LED calculator will help you calculate the currents and resistor values you will need to brightness-match LEDs of different colors.
For example, you might be building a panel with multiple color indicators and you want their perceived brightness to be the same, or you are wiring up an RGB LED for white light.
Results are calculated based on the specified LED parameters in relation to the target (max) current or intensity (brightness).
Since the current vs. intensity curve of the LEDs are not known and manufacturers differ, these values should be treated as indicative and not final.
Best results are achieved when targetting currents at or near the rated current and using LEDs with similar optical characteristics Results may still require fine tuning to get perfect. .
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Source Voltage V
Target
Target Intensity mcd
Resistor Series
Current (max) Intensity
E12 E24 E48 E96 Exact
Name
Intensity mcd
at Current mA
Voltage (VF) V
Resistor Ω
Current mA
Intensity mcd
Error
In this calculator I am, somewhat unscientifically, using intensity (referring to luminous intensity) and (perceived) brightness interchangably.
It is designed primarily for LEDs being viewed directly (not used for illumination) and in this case it makes little sense to speak of brightness and intensity separately.
Some notes on terminology, LEDs and units:
Photometry is the science of measurement of light in terms of how it is perceived by the average human eye.
Such measurements are called photometric as opposed to radiometric, which instead represents actual, physical, energies.
Brightness is the perception elicited by the luminance of a visual target, meaning it is a photometric measurement.
This is a measure of what is perceived by an average human, regardless of other factors.
Luminance is the photometric measure of the luminous intensity per unit area of light in a given direction.
This means it can represent the light reflected off a surface, but also light in transit across an area.
Luminous intensity - the wavelength weighted (ie. photometric) power emitted by a light source in a particular direction.
This says nothing about the total amount of light, only how much is travelling in one specific direction.
Candela is the SI unit used to specify luminous intensity.
It is thus photometric, and measured in a particular direction.
LEDs are, by industry standard, specified in candela (cd), commonly millicandela (mcd) for small LEDs.
Since candela is photometric, no such rating is provided for invisible light LEDs such as infra-red, ultra-violet or beyond.
The direction chosen for the luminous intensity measurement is usually where it is the highest, the peak intensity.
This direction is typically the dead-center of the intended direction for light emission.
The viewing angle specification tells you the number of degrees between the directions where luminous intensity is at 50% of the specification.
This means that any given LED light source will have a higher candela rating, if provided with a lens to produce a narrower viewing angle.
A wider viewing angle will subsequently result in a lower candela rating, even though the total amount of light emitted remains the same.
As such, luminous intensity is not a great measurement for illumination purposes, where the total amount of light provided is of high concern.
When dealing with illuminating LEDs, LED modules or LED fixtures, the SI unit lumen, a measurement of luminous flux, is typically used instead.
For invisible light LEDs or LEDs designed for non-viewing purposes, the SI unit watt, a measurement of radiant power/flux/energy, is typically used.