What are the main components of LED luminaires?

Brightness, lamp life and efficiency of LED luminaires

Introduction

A typical LED luminaire has four main components: an LED Emitter, the device's heat sink, driver and dimming control, and dimmer optics.

The transmitter consists of the matrix, a heat sink, a lens, and an external housing. The chip is the actual LED chip in the transmitter.

The color of light is determined by the energy gap in this semiconductor. The heat sink that is part of the transmitter keeps the chip away from heat and leads it to the device ground (larger the device heat sink ).

The electronics in the power supply are designed to limit the drive current to the specifications of the LED. In this regard, LEDs are very sensitive; too much current can shorten their useful life from 50,000 hrs. to nothing in an instant.

This is why manufacturers warn that the light should not be used above a certain temperature. Control of the drive current is critical to the brightness and lifespan of the LED.

An LED is a current driven device, which means that the intensity of light depends on the amount of electric current flowing through it. Device designers try to design their lights with as high a drive current as possible, but there is a three-level relationship between brightness, lamp life, and the luminaire's ability to dissipate heat.

LEDs are brighter when the current is high, but lose their effectiveness if their operating temperature is allowed to rise.

The scale the appliance designer can find will also depend on the limitations imposed by emitter spacing and the efficiency of heat management.

This is why almost all LED devices have large sinks and heat sinks.

The deadly effect of overheating has prompted some manufacturers to provide overheat protection by automatically increasing the speed of the cooling fan and at some point automatically reducing the power or shutting off the assembly if the light approaches the line red, to draw the user's attention to the heat problem.

This can usually be remedied by providing shade or better ventilation.

There are different ways for manufacturers to organize gradation. One method is to vary the drive current using pulse amplitude modulation (PAM). PAM is a current control method that uses very fast on / off switching to limit the current. By varying the timing of the switching, the current can be reduced to dim the LED.

A dimmable luminaire with PAM will shut off abruptly before it reaches full dim. The other way to reduce LEDs is to use pulse width modulation (PWM) downstream of the driver. The PWM modulates the intensity by varying the duty cycle at high frequency. This allows for almost zero smooth gradation.

For LED lamps marketed for cinema and television, the frequency of the electronic power supplies and the PWM dimmer over 20,000 Hz and does not pose a flicker risk at normal frame frequencies. Nila actually tested at up to 7,000 frames per second without capturing any flicker.

However, cheaper LEDs designed for consumer markets or clubs may use power supplies that operate at 1kHz or even lower, which poses a definite risk of flickering, especially when the LED is photographed at a frame rate. of view higher than normal. Testing is recommended.

The optical components of LEDs, lenses and reflectors, extract light from the chip and shape the projection of that light into a focused beam. A total internal reflection (TIR) lens is a small, molded lens used to capture light that is emitted at 180 from the array and shapes it into a manageable beam of light. Advances in optics accounted for the lion's share of the improvement in LED light production in the early years of their development.

More recently, improved chip technology and chemistry and better thermal management by the chip itself have greatly contributed to improved performance.

As mentioned earlier, some LED lights use interchangeable optics. A thin sheet of glass covers the chip to protect it. The optics should be kept clean, however, do not use solvents or window cleaners as they may have undesirable effects on the assembly. Manufacturers recommend using a soft cloth with isopropyl alcohol to clean the protective glass. Use water with mild soap for the optics.

Power factor

Power factor can be a concern when using very large numbers of LEDs. Color Kinetics and NILA devices are fully power factor corrected. Many of the devices described in this chapter may or may not have power factor correction. If they don't, you can expect to see a power factor of around 0.70.

In a large installation, this could create a significant non-linear load impact. Check the manufacturer's specifications.

LED lifespan

The LEDs are very rarely faulty or go out suddenly (except severe overheating). Normally, they slowly fade over time at a relatively constant rate.

Their useful life is defined in terms of light retention - the number of hours the emitter will operate on average before the light output drops below a given percentage of the initial light output. .

For example, the transmitter manufacturer will specify that an LED will produce at least 70% (denoted L70) of its initial output for 50,000 hrs. , when driven at a particular current and at a particular junction temperature. This is also sometimes indicated as L75 or L50 (75% and 50% respectively).

The L value that the manufacturer uses to produce their advertised lamp life figure makes a big difference. In practice, a light that emits less than 70% of its initial output would be considered fairly useless in our business. Depending on how the light designer configures the electronics and heat dissipation, and which LED chooses the estimated lamp life can vary a bit.

Manufacturers of lamps used in our industry advertise the lamp life of 20,000 to 100,000 hours. If you ran a 50,000 hours of LED 8 hours a day, every day including weekends and holidays, the light would lose ten% of the original output in about 6 years. At this rate, it would take a little over 17 years to achieve 70% efficiency.

Of course, once the LEDs are worn out, you just have to replace the whole fixture. Another factor that is easily overlooked in all of this is that in theory the circuit components used in control electronics have a longer average time to failure than the LEDs themselves and can end up being the weak link.

 

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