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Terminology of SMD LED and DIP LED


There have kinds of terminology for the SMD LED and DIP LED when we read the datasheet of those 5mm IR LED or some common Light Emitting Diode. Today we going to make some explanation for that.

Luminous intensity: LV(cd) 1cd=1000mcd

Represents the brightness seen from a certain direction. The unit is "cd".
When comparing the luminous intensity, you must pay attention to the azimuth angle. Luminous intensity defines the amount of light per unit solid angle.
This is a lens composed of an LED package that can gather light to output in a certain direction (using the lens to gather light). Even if the light output is small, the light can also be used to increase the luminous intensity.
When comparing technical data, it must be judged based on both the azimuth angle and the luminous intensity.

Normally "mcd" represents the common emtting color such as red LED, green LED, blue LED, Yellow LED, Amber LED, Orange LED, purple LED ect visable color.


And for White SMD LED or white Through-hole LED, we usually use the "lm"

The total amount of light emitted from the light source. The unit is lm (lumens).

5mm white LED

We can also see some wavelength from the datasheet, there will have some unit like λP or λD, what does they means? Is it there have two kinds of wavelength from the same LED?

λP [nm]: Peak wavelength

The wavelength with the highest spectral output value from the LED light, the unit is "nm (nanometer)".
Although the LED lamp will be designed according to the peak wavelength, the dominant wavelength will still be used when comparing the actual wavelength.

λD [nm]: Dominant wavelength

Generally speaking, LEDs will express colors by wavelength. The wavelength is marked by visual color, but this is not the peak of the emission wavelength.
The unit is "nm (nanometer)".

630nm and 520nm LED

There are information about the visable colored LED. For white LED, we will use different word: Chromaticity coordinates x, y:

In a 2-dimensional rectangular coordinate system, to display the stimulus value of the LED luminous color, the x y coordinate system is generally used.

There number inside of the picture like 2000, 3000, 4000, 6000, 10000 represent the color temperature, which defines the color appearance of a white LED. CCT is defined in degrees Kelvin; a warm light is around 2700K, moving to neutral white at around 4000K, and to cool white, at 5000K or more.

CIE 1931 xyY color space


The luminous range of the LED. The unit is "degree".
When the LED package is tilted to observe the change in light output, from the output peak value to the recognizable angle characteristic value, and the angle of half the brightness of the output peak value is multiplied by 2 (the front side is symmetrical), it is called the right angle.

5mm IR LED with different angle

Forward voltage:

When a forward current is applied, the voltage generated between the positive and negative electrodes. The unit is "V (Volt)".

Reverse current IR [A]:

The leakage current generated when voltage is applied in reverse between the positive and negative electrodes. The unit is "A (ampere)".

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