Dear Reader:

We believe generally that the typical focus during an LED buyer’s due diligence is on what can be expected during the initial performance of a new lighting system – hoping that once installed, everyone will look up and ooh and aah – but with not enough importance placed on anticipated performance over the length-of-life of that system.

That said, looking for the ‘Rated Life’ metric in a product line’s specifications will pay huge dividends.

Energy Star requires that a fixture be tested at three different temperatures over a period of 6,000 hours. This provides the buyer with an understanding of how long a fixture can be expected to functionally live – as defined as outputs that are no lower than 70% of its original lumen output.

This method, known as TM-21, provides mathematical calculations that simulate the full length of life for each temperature tested.

Why 70% as the tipping po...