L: Defines the percentage of lumens compared to the initial lumens. It means that the luminous flux of the luminaire that has been working for a period of time and the initial luminous flux of the luminaire are used for the ratio operation. L70 indicates that the luminous flux has attenuated to 70% of the original luminous flux, L80 indicates that the luminous flux has attenuated to 80% of the original, and L90 indicates that the luminous flux has attenuated to 90% of the original.
B: The value represents the failure data at the L data. B10 means that 10% of the LEDs cannot meet the requirements.
Therefore, the L/B value represents the actual life in a certain hour. This metric is commonly used to estimate the longevity of light sources and is important for planning maintenance schedules and replacements in lighting systems.
For example, 50000h (L90/B10), that is, the time it takes for 10% of the luminous flux output of the product to drop below 90% of the initial value is 50000 hours. Conversely, it means that LED products have the reliability that 90% of the products still have a light decay of less than 10% after working for 50,000 hours.
L70B50 represents the time it takes for a light source to reach 70% of its initial lumen output, with a maintenance factor of 0.5. In simpler terms, it indicates the point at which the light source has depreciated to 70% of its original brightness, considering a maintenance factor of 0.5.
With the upgrading of lighting technology and the maturity of broadcasting technology, customers choose more lamps that meet the L90B10 standard based on their advantages such as high brightness, long life, energy saving, high quality, and compliance with safety standards.
But because determining the “L/B” value using standard methods is time-consuming and expensive, other methods have also been proposed: on the US Department of Energy’s Lighting Facts label, one of the lumen depreciation, product warranty, or life estimated by accelerated testing can be used. Item or items to replace the original “life” item.
LM79
LM79 specifies the test methods for the total luminous flux, electric power, light intensity distribution, color parameters, color uniformity, and other parameters of the product. This standard includes LED SSL products as well as integral LED lamps (required to be driven only by AC or DC). This standard does not cover SSL products (LED chips, LED packages, LED modules, etc.) that require external drive circuits or external heat sinks. Generally speaking, the test can be divided into integrating sphere test and goniophotometer test:
Integrating sphere test: voltage, current, power, color temperature, color rendering index, spectral distribution.
Goniophotometer test: voltage, current, power, total luminous flux, light intensity distribution, color uniformity
For the LM79, the integrating sphere test does not measure the luminous flux, otherwise, very complicated steps such as auxiliary lights are required.
LM80
LM80 refers to the measurement of light sources, and “light source” refers to packages, arrays, and modules only. The main points are as follows:
a. The aging process is separated from the testing process. During the aging process, the temperature of the Tc point must be strictly controlled at 55 degrees, 85 degrees, or the temperature agreed by the supplier. After aging to the specified test interval, return to the test environment for photometric testing.
b. It is required to test the luminous flux and color parameters, and the specific test methods are not strictly regulated. The following are the original words in the standard: Photometric measurements shall be in conformance with the appropriate laboratory method for the LED light source under test
c. There are high requirements for environmental control, temperature control of Tc, and power supply equipment.
d. There are detailed requirements for tracking and recording samples and the aging process.
LM82
LM82 is the follow-up standard of LM79, which specifies the electrical and optical tests of LED light engines and integral LED lamps at different temperatures after elevated temperatures. The main points are as follows:
a. The sample to be tested needs to give the temperature monitoring point Tb and the temperature monitoring point Td of the power supply (not mandatory).
b. Initial test—according to Section 9 of LM79, test the power, luminous flux, and color parameters at an ambient temperature of 25±1°C, and monitor the Tb value at this time, which is recorded as Tbi.
c. Calibration test—adjust the ambient temperature to make Tb reach the ambient temperature of the initial test (25±1°C), then test the power, luminous flux, and color parameters, and monitor and record the Tb value at this time, which is recorded as Tb0.
d. Temperature rise test—adjust the ambient temperature to make Tb reach Tb0+25°C, then test the power, luminous flux, and color parameters, and monitor and record the Tb value at this time, which is recorded as Tb1.
e. The second temperature rise test—adjust the ambient temperature to make Tb reach Tb0+50°C, then test the power, luminous flux, and color parameters, and monitor and record the Tb value at this time, which is recorded as Tb2.
f. According to the processing method specified in the standard for the data measured above, obtain the photometric characteristics after increasing the temperature.
g. It is mentioned in the standard that it is recommended to use a temperature-controlled integrating sphere for temperature control. Other methods must require that the temperature of the Tb point can be well controlled without affecting the photometric test.
TM21
TM-21: mainly combine the LM80 report and ISTMT report to estimate the life of the whole lamp.TM21 provides a processing method for the data measured by LM80, mainly including the following contents:
a. The data fitting method in the form of the exponential function is given.
b. The correction method for the fitting lifetime (70% light decay lifetime) is given.
c. The detailed expression method of life is given.
d. The interpolation method for calculating the life at a given point temperature is given.
ISTMT(In-Situ Temperature Measurement Test)
ISTMT stands for In Situ Temperature Measurement Test, which is the measurement of the temperature of the LED source box in the LED system (luminaire or lamp). Simply put, as far as the internal LED temperature of the luminaire is concerned, measurements must be made at the temperature measurement point (TMP) indicated by the LED package manufacturer.
