In addition, when choosing LED lights, some people have the following misunderstandings!
Myth 1: the expectation of actual service life is too high.
LED manufacturers expect LED life to reach 100000 hours MTBF
(mean time between failures, a standard used by traditional lamp manufacturers to measure the life of light sources). But, like all basic light sources, LEDs
The luminous flux lumen also decays over time. Therefore, although the LED light-emitting time can be very long, MTBF is not the only consideration to determine the service life.
The attenuation of LED lumens is affected by many environmental conditions such as ambient temperature, humidity and ventilation. Lumen attenuation is also affected by control, thermal management, current levels, and many other electrical design considerations (the above quote from CK).
Many salesmen may provide some vague information to customers for some reason when selling led, which may cause misleading. For example, the service life of LED is about 100000 hours, which refers to the manufacturer's expectation
Service life of LED. As the light source of illumination, the brightness of the lamp has a process of gradual attenuation and darkening (such as fluorescent lamp)
, energy-saving lamp), this process is referred to as light attenuation. On application level LEDs, when the light attenuation exceeds 50%, people's eyes can obviously feel the change of brightness. At this time, we think the product brightness is not suitable for lighting. Many manufacturers and engineers often find that the brightness of the LED is obviously not as bright as that when it was just installed, or even almost none, after using the low-cost led for about three months to half a year. It is precisely because the reason of LED light decay is not taken into account. To sum up, when purchasing LEDs, we should pay attention to its light attenuation speed, not its use time.
Myth 2: regard the actual luminous angle as an effective angle.
The luminous angle of LED is divided into effective angle and actual luminous angle. The angle between the direction in which the luminous intensity value is half of the axial intensity value and the luminous axis (normal direction) is the effective angle. Twice the half value angle is the viewing angle (or half power angle), which is the actual luminous angle. The angle beyond half of the axial strength is not included in the effective angle in practical application because the light is too weak. (the following figure is a side view of piranha particles, and the included angle between solid line and dotted line is not included in the effective angle)
Therefore, when purchasing products, we should pay attention to the actual luminous angle of products. When calculating the number of products used in the project, the actual luminous angle shall prevail, and the effective luminous angle can be used as a reference value.
Myth 3: the higher the power, the higher the brightness.
The brightness of LED is measured by luminous intensity. Luminous intensity refers to the luminous intensity in the direction of normal line (for cylindrical luminous tube, it refers to its axis), that is, the luminous flux emitted by unit solid angle, and the unit is candela,
cd)。 Due to the low luminous intensity of general LEDs, the luminous intensity is usually measured in millicandela (MCD). Generally speaking, the light source will emit its luminous flux in different directions with different intensities. The visible light radiation intensity emitted by the unit solid angle in a specific direction is called light intensity, which is referred to as axial brightness for short.
The concept of electric power is introduced from the amount of work done by force in equal time. If the current does work quickly, the electric power is large; If the current works slowly, the electric power will be small, or in the same time, the more work the current does, the greater the electric power. On the LED, it is not that the greater the power, the higher the brightness of the product. Taking the three lamp red LED of Yimei electronics as an example, when the axial brightness is 1200mcd, the current is 40mA and the power is 0.48w; Under the same brightness, the current of three white LEDs is 18ma and the power is only 0.24w; It can be seen that the power of the two lights is different under the same brightness. So when we buy led, we should pay attention to its axial brightness, not power.
Myth 4: about the purchase of white LED modules.
1. High brightness (blue-green) white LED is very sensitive to static electricity, which is determined by the characteristics of LED itself. Exceeding the maximum forward DC current and maximum reverse voltage it can allow may cause damage or breakdown of the LED. For example, for the three lamp LED module, each lamp will have an anti-static resistance, plus the resistance for current limiting, there are four in total. The anti-static resistor can effectively suppress the damage caused by static electricity to LED.
The current limiting resistor mainly limits the current of the whole module. This design can effectively improve the overload resistance of LED and enhance the stability of products. At the same time, whether the four resistance marks are complete is also a sign that can simply identify whether the quality of the module is stable or not.
