Are all LEDs created equal?

The following context explains differences between LED lights of various types and qualities. The objective is to educate the reader to enable him or her to make a wiser decision prior to purchasing any product containing LED technology. Other educational content related to LED lighting can be found on this website, or at http://www.LunarAccents.com. Unfortunately, many of those who at least somewhat familiar with basic LED technology, lack the ability to recognize primary differences between LED lights. Many buyers looking to purchase an LED product, tend to search out a product featuring the largest overall quantity of LED lights. This common mistake stems from the believe that more LED lights equals more light output. However, not all LEDs are created equal! Anyone purchasing an LED product for any reason, should start by considering the luminous output required for their specific lighting application. Luminous output measured in lumens, describes the total visible light output from the device, in all directions. Do not confuse this with luminous intensity, which describes only the intensity within a given distance and range of angular degrees. A standard 100 watt incandescent light light will produce approximately 1300 lumens. How much light does your specific application require? Keep in mind that the capabilities of some LEDs exceed those of others. An array of forty 5mm LEDs may produce about 80 lumens, as opposed to an array of forty high power LED lights that might produce as much as 4000 lumens. You will find a dramatic cost difference between the array of 5mm LEDs and high power LEDs. Even though both arrays contain an equal number of total LED lights, the capabilities of the high power LEDs far exceed those of the less powerful 5mm devices. You have a rough idea as to the total luminous output your lighting application requires. The next step involves calculating for efficiency. Two types of efficiency commonly associated with LED lighting include "power efficiency" and "cost efficacy". Power efficiency compares the total light output measured in lumens, to the overall power dissipation measured in watts. The overall power dissipation includes all wasted energy dissipated in the form of heat. To
calculate for power efficiency, you must know two variables, including the luminous output in lumens and total power dissipation in watts, or operating voltage and total amperage. If you only have the voltage and amperage, multiply them by each other to obtain the total power dissipation of the device. The next step is to divide the luminous output by total power dissipation. If an LED device provides 100 lumens and dissipates 5 watts, divide 100 into 5 for your answer. The efficiency of this device equals "20 lumens per watt". The process to calculate cost efficiency is very similar to that utilized to calculate energy efficiency. Simply divide the total luminous output of your LED product by the total cost. Your answer in "lumens per dollar" provides an indication of the light output you will receive per each dollar paid for this specific LED device. For example, an LED array producing 100 lumens at a total cost of $20.00, offers a cost efficiency of "5 lumens per dollar". So far we have discussed the concepts of LED efficiencies, but there are other reasons why all LED lights are not created equal. Several of them include color consistency, extent of life, and consistency of luminous output. These factors are determined by the following three primary factors: LED quality, LED binning, LED integration by the designer. The following context will discuss each of the three factors in greater detail. High quality LEDs should always appear of the exact same color to the naked human eye. The LED lights should also appear uniform in luminous intensity. Color variations and variation in luminous output may become apparent with LED lights of lower quality. To test for consistencies, connect the LED product or LED array to an adjustable power supply. Start by setting the output voltage on the power supply to the required operating voltage for the LED device. Slowly decreased the voltage until the LEDs begin to dim out. This is the operating range where inconsistencies in color and luminous output will become most apparent. LEDs of higher quality should appear uniform, and exhibit the same color and output characteristics. However, low
quality or cheap LEDs may not. Some may exhibit variations in color as well as luminous output. In some cases the LED manufacturer's "binning" process can be blamed for apparent inconsistencies in color and luminous output. Subsequent to LED lamp production, the manufacture will subject each LED to a testing process in order to identify and sort individual LEDs based on specific characteristics. Among these characteristics include the voltage, optical wavelength, and luminous output. The binning process becomes the most critical aspect associated with uniformity among various LED lots or batches.
Unfortunately, some LED manufactures do not pay enough attention to the quality of their binning procedures. As an end result, variations in LED characteristics may become apparent during operation. Low quality LEDs may feature a reduced life span. Many designers and LED manufacturers refer to and describe LED life in terms of lumen maintenance. Lumen maintenance indicates the relative light output after a specified period of accumulative operation. LED lights of uppermost quality may feature a lumen maintenance of 70% at fifty thousand hours. However, cheaper LEDs may only offer 40% at fifty thousand hours. Aside from overall LED quality, another factor affecting lumen maintenance includes good thermal management. However, good thermal management becomes a factor of the system designer, more so than of the LED manufacture. The system designer must consider LED die temperatures during operation, and attempt to incorporate a means of cooling such as circuit board copper or an external heat sink.