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Difference between revisions of "LED"
add section about reading datasheets
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Some LED's are also binned by [[Terminology#Vf|Vf]], or forward voltage. | Some LED's are also binned by [[Terminology#Vf|Vf]], or forward voltage. | ||
==Datasheets== | |||
Manufacturers usually have a datasheet available for their different models of LED. These have a great deal of valuable information, including the binning and labeling information (sometimes in a separate document) which tells you how to read product number codes and codes for the different bins for output, tint, forward voltage, and CRI. Different tint bins are described with coordinates and a chart is usually included showing the tint bins graphically along the black body curve. The datasheet also includes physical dimensions of the LED and characteristics like viewing angle. Graphs tell how the output varies with temperature and current, as well as how the forward voltage increases for given currents. | |||
Here's an example: A manufacturer makes a LED available in bin X that gives 120 lumens at 350mA, but you want to know the output at 1500mA. In the datasheet find the relative output (or relative luminous flux) graph. At 350mA the line should indicate a relative output of 100%. To find the output at 1500mA, find 1500mA on the horizontal axis, go up to the line and then over to the relative output reading, which might be 320%. So just multiply 120 lumens times 3.2 to get an output of 384 lumens at 1500mA. | |||
Since some LED's are now binned at 85 degrees C instead of 25 degrees, the datasheet allows you to correct the output for temperature and make fairer comparisons between LED's. | |||
The datasheets usually do not tell you the bins that are actually available. Just because there are 80 different tint bins does not mean you can get the LED in all of those tints. And while a datasheet might show a maximum output bin, realistically that may not be available or sometimes even higher bins will be available. Manufacturers usually update the datasheets a few times during a product's lifetime. | |||