Comparison between LED Lights and Conventional Lamps
Nowadays, replacing conventional lamps with LED lights fixtures have been a trend all over the world. How to compare the LED light fixtures with conventional light fixtures to assess a lamp’s property? In this article, we will make comparison based on basic concepts like energy efficiency, lamp effectiveness, luminous depreciation.
The assessment of the energy efficiency of lighting systems begins with the effectiveness of the light source, but does not end there. Other factors, such as ballast or drivers, optical losses and thermal factors also determine the final energy efficiency of any lighting system.
For traditional lamps, the efficiency expressed in lumens per watt (Lm / W) is measured under steady state conditions at 25 ° C ambient temperature. The Efficiency of LED Lighting can’t be measured in this way. LED luminaires generate heat when used continuously, which can significantly decrease their light output and effectiveness. For this reason, LED luminaires are associated with heat sinks to conduct heat out of the device; However, there are no “standard heat sinks” for LED luminaires, which complicates their performance measurement and comparison with other light sources.
Output and light output data shown on the LED plugs are usually very short term (25 milliseconds or less) measurements taken at a calculated junction temperature (TJ) of 25 °C, generated by using a short current pulse. The short current impulse avoids significant warming of the LED and therefore results in higher measured light output and efficiency than for continuous operation.
To better estimate actual performance, some LED Lighting manufacturers provide additional data to adjust light output values in TJ = 25 °C during anticipated operating temperatures. These data indicate the output of LED light at TJ = 75 °C is approximately 10% to 15% less than the light output rated at TJ = 25 °C. This estimate should be used only as a general indication, and not a substitute for detailed evaluation of individual LED products.
Lamp effectiveness is a more accurate way to measure the performance of both LED luminaires and traditional luminaires. The metric used for comparison is called luminaire efficiency, expressed in lumens per watt (lm / W).
The efficiency of the luminaire is typically less than the efficiency of the source due to optical losses and in some cases, these are factors affecting thermal performance of the light source (eg for LEDs and fluorescent lamps).
Unlike conventional light sources that reduce in output and eventually fail, LED products do not normally suddenly fail. Instead, the light output reduces over time.
The service life for traditional light sources is based on lamp failure, with a medium lumen output, measured at a lamp life percentage, typically 40% for fluorescent lamps and metal halide lamps. LEDs can continue to operate for a long time after their light output has dropped below useful levels.
Currently, linear high performance fluorescent lamps offer average lumens that are as high as 95% to 97% of their initial values. Depreciation of lumens for LED lighting is still not well understood; With a useful life defined as L70, a linear depreciation curve would involve lumen mean values of about 85% of the initial production. To achieve comparable efficiency in the luminaire.
In this case, LED luminaires should have an initial effectiveness superior to their fluorescent or other counterparts.
As mentioned above, lumen output for a fluorescent lamp or metal halide is measured at 40% of rated life. For better performance T8 fluorescent lamps, lamp life can range from 30,000 to 46,000 hours, which means that the output of the lumen (and say luminaire Efficiency) would occur after about 12,000 to 18,000 hours.
The main manufacturers of LED Lighting have in the design (L70) to value the 50,000 hours; The actual operation time to achieve the average efficiency luminaire will vary with the quality of LED products.