LEDs Test Terms and Definitions

1 LED
In addition to the semiconductor lasers, when the current motivates the semiconductor diodes can emit the optical radiation. Strictly speaking, the term LED should be only applied to emit the visible Diode; The diode which can emit near-Infrared radiation is called infrared light emitting diode (IRED, Infrared Emitting Diode); The emission peak wavelength is limited near the shortwave, the diode which has part of the ultraviolet radiation is called ultraviolet light emitting diode; However, customarily the above three kinds of semiconductor diodes are collectively called LEDs.

2 Optical axis
It refers to the maximum luminous intensity (or radiation intensity) centerline direction.

3 VF Forward voltage
It refers to the voltage drop between the poles when the positive current through the leds is the fixed value

4 IR Reverse current

It refers to the current through the light emitting diode when the reverse voltage added on both ends of the emitting diode is the fixed value.
5 VR Reverse voltage
It refers to the voltage drop between the poles when the reverse current through the LED device under test is the fixed value.6 C Capacitance
It refers to the capacitance on both ends of the LED under the regulation of the forward bias and frequency.7 Switching time
The minimum and maximum ratings involved in the following concepts are 10% and 90%, unless otherwise noted.7.1 td(on) Turn-on delay time

It refers to the time interval between the lowest rating of the input pulse front porch and the lowest rating of the output pulse front porch.

7.2 tr Rise time

It refers to the time interval between the lowest rating and the highest rating of the output pulse front porch.

7.3 ton Turn-on time

It refers to the time interval added in the device between the lowest rating of the input pulse front porch and the highest rating of the output pulse front porch.
ton= td(on)+tr7.4 td(off) Turn-off delay time

It refers to the time interval added in the device between the highest rating of the input pulse back porch and the highest rating of the output pulse back porch.

7.5 tf Fall time

It refers to the time interval between the highest rating and the lowest rating of the output pulse back porch.

7.6 toff Turn-off time
It refers to the time interval added in the device between the lowest rating of the input pulse back porch and the lowest rating of the output pulse back porch.
toff =td(off)+tf

8 Φv Luminous flux
It refers to the luminous flux emitted from the optical window of the device when the forward current through the light emitting diode is the fixed value.9 Φe Radiant power
It refers to the radiant power emitted from the optical window of the device when the forward current through the light emitting diode is the fixed value.10 ηe Radiant power efficiency
It refers to the ratio of the radiant power emitted by the device and the electrical power of the device (the positive current IF multiplies the forward voltage VF):
ηee/(IF•VF)
Note: In order to avoid being confused with other terms, it can be referred to as the radiation efficiency (Radiant efficiency).11 ηv Luminous flux efficiency
It refers to the ratio of the luminous flux Φv emitted by the device and the electric power of the device (the positive current IF multiplies the forward voltage VF):
ηvv/(IF•VF)
Note: In order to avoid being confused with other terms, it can be referred to as the luminous efficiency.
12 Luminous (or radiant) spatial distribution diagram and the related properties

12.1 Iv Luminous(or Radiant) intensity
The luminous (or radiant) flux emitted by the light source within the per unit solid angle can be expressed as Iv = d Φ/d Ω. The concept of the luminous (or radiant) intensity requires to assume the radiation source as a point radiation sources, or its size and light detector area is small enough compared with the distance from it to the light detector, in this case, the luminous (or radiant) intensity on the light detector surface follows the inverse distance square theorem: the E = I/d2. Here I is the intensity of the radiation sources, d is the distance from the radiation center to the detector center. This situation is called the far field conditions. However, in many applications, the distance of measuring LED is relatively short, the relative size of the source is too big, or the angle of the detector surface is too big, it is the so-called near field conditions ( A Near-field Goniospectroradiometer for LED Measurements ). At this time, the luminous (radiant) illuminance depends on the correct measurement conditions.

12.2 Averaged LED intensity
The ratio of the flux Φ irradiated on the photodetector from a certain distance with LED and the solid angle Ω formed by the detector . The solid angle can be calculated by using the proportion S of the detector to divide the square of the measuring distance.
I=Φ/Ω=Φ/(S/d2)
Standard conditions A and B recommended by CIE are used to measure the average LED intensity under the near field conditions, can be respectively expressed with symbols ILED Aand ILED B. Use symbols ILED Ae and ILED Av to respectively represent standard conditions A, the measuring average LED radiation intensity and average LED intensity .12.3 Luminous(or Radiant)diagram
Reflecting the light-emitting (or radiation) strength space distribution characteristics of the device:

Iv(or Ie)=f(θ)

Note 1: unless otherwise provisions, the light-emitting (or radiation) intensity distribution should be included within the plane of the mechanical axis Z.
Note 2: if light-emitting (or radiation) intensity distribution pattern has the symmetry characteristics of rotating with respect to Z axis, light-emitting (or radiation) intensity space distribution only provide a plane.
Note 3: if there is no symmetry characteristics of rotating with respect to Z axis, the light-emitting (or radiation) intensity distribution of all kinds of angle θ should have requirements, X, Y, Z direction have the detailed and defined specification requirements.

12.4 θ1/2 Half-intensity angle
In the light-emitting (or radiation) intensity distribution pattern, the angle is formed when the light-emitting (or radiation) intensity is larger than half the maximum intensity degree.

12.5 Δθ Misalignment angle
In the light-emitting (or radiation) intensity distribution pattern, the angle between the maximum light-emitting (or radiation) intensity intensity (optical axis) and the mechanical axle Z.

13 Spectral characteristic

13.1 Peak-emission wavelength λp
The largest wavelength of spectral radiant power

13.2 Spectral radiation bandwith Δλ
Spectral radiant power is equal or greater than half of the maximum wavelength interval.

13.3 Spectral power distribution P(λ)
In the ray radiation wavelengths range, the radiation power distribution of each wavelength.

LEDs Test Method: The Electrical Characteristics Testing Methods

LEDs Test Method: Light Characteristics Measuring Methods

LEDs Test Method: Luminous Flux and Luminous Efficiency

LEDs Test Method: Radiation Flux and Radiation Efficiency

LEDs Test Method: Peak Emission Wavelength, Spectral Radiation Bandwidth and Spectrum Power Distribution


LEDs Test Method: Photoelectric Characteristics Testing Method – Switching Time