Understanding Relevance Of LED lamp

LED lamp is regarded for its energy efficiency, long life span, high Colour Rendering Index (CRI) and wide Correlated Color Temperature (CCT) range. Unlike incandescent bulbs, LEDs produce heat but do not dissipate, it makes them as cooler lamp. LED lamps are most inexpensive lamps considering their energy payback period over the useful life period. These lamps are more sustainable as nearly 90% of material used for manufacturing it is recyclable. This article discusses these facts in detail to make LED lighting as an attempt for energy saving in India.

Efficiency of LED lamp

  Each lamp has its own physics of working to produce light from heat generated. The energy efficiency of CFL and LED are shown in Fig-3. The graph is based on power rating of lamp i.e., energy level. The graphs shows us that at lower energy level (low power rating), LED lamp is more efficient than CFL counterpart.

  The graph from Figure 2 helps us to confirm that for lower power rating (below 8 W) LED is more efficient than its equivalent CFL. e.g. - If we would compare a 5 W CFL with LED lamp, then LED shows that light output is 5*65=325 lm and CFL lamp output is 5*45=225 lm. The LED lamp here is 1.5 times more efficient.

Figure 1: LED Lamp...

Figure 2: Lumens (Light Output) Vs Power Input (Watt)...

LED Lamp saves energy during dimming

  It is a well known fact that when we require lesser light output, then lamp may be operated at lower power level. It can save energy. This may not hold true for all lamps in a linear relationship. Refer to Fig-2. It shows that when 60 W GLS lamp operates at 30 W [50% Dimmed], then its light output actually reduces to 20% of its rated lumens. Hence, we won’t get any saving. The quality of light output is deteriorated from yellow/orange to orange/red colour rendering. The other lamp CFL also gets less efficient when dimmed because they become cold and result in less light output. But in case of LED lamp, dimming will result less operating temperature (hot), so their efficiency increase. This provides us more light output for same power input compared to other lamps.

  It includes that LED lamp may be more efficient at dimmed condition than at full load.

LED lamps are less hot

  It is known that LED lamp converts only 10% of the electrical energy input into light energy. It means that now still 90% of energy is turned into heat. But the power consumptionof LED lamp is much lesser than that of incandescent lamp/CFL, so the amount of heat developed is also less. For a well designed LED lamp will have heat sink to take the heat generated to outside. Incandescent lamps convert only 1.5% of electrical energy into light energy output. The absolute amount of heat in LED lamp is 90% of 6W while for incandescent lamp it is 98.5% of 60W. [6W LED lamp light output = 60W Incandescent lamp].

Figure 3: Performance of lamp during dimming...

Non-uniform light output

  We are aware that a LED lamp is more efficient at low power level. It means that instead of using 6W LED single lamp, we can use 3 lamps of each 2W or two lamps of each 3W rating. In this fashion of LED lamp distribution in a given room will provide is a comparatively uniform illumination in given room surface.

  So, the disadvantage of non-uniform light / concentrated light output of LED lamp may be overcome. It is essential because in India the domestic market is asking for a 60W replacement solution. A preferred lamp for rural India will be of LED lamp of 120 to 160 lumen output for 2W rating or 210 lumen output for 3W LED lamp. By using more lamps simultaneously will be much more convenient. In European countries a house has now average of lamps is 42 today as compared to only 3 lamps in 1950.

Cheaper for useful life period

  At present, customer may view that LED lamp is expensive because he consider lamp as a product rather than a utility device. When we purchase a lamp, we are not only buying a piece of hardware, but requirement of light. i.e., combination of hardware and energy.

  The LED lamp has lumen efficiency of 12% more than that of the incandescent lamp of 1.5% and CFL has 5-6%. Another factor is that the average life time period of the incandescent lamp is 1000 Hrs while LED lamp has 25,000 Hrs.
Consider that a 6W LED lamp replaces a 60W Incandescent lamp for a given installation. The energy calculations for 6 hrs daily use are:-

A) Incandescent lamp:

1. Power rating (P) = 60W
2. Daily Energy used = 60*6=360 Wh
3. Annual Energy consumption 
= 360*365
=131400 Wh
=131.4 kWh
4. Annual Energy Bill @ Rs-5 per kWh = 131.4*5 = Rs 657/-

B) LED lamp:

1. Power rating (P) = 6W
2. Daily Energy used = 6*6 = 36 Wh
3. Annual Energy consumption
= 36*365
= 13140 Wh
= 13.14 KWh
4. Annual Energy bill Rs-5 per KWh = 13.14*5 = Rs 65.7/-
Therefore saving in annual energy bill 
= Rs (657-65.7)
= Rs 591.3/-
5. Percentage saving in annual energy bill = (591.3/657)*100
= 90%

  This saving shows that 6W, LED lamp cost is earned back in a year approximately.

Conclusion

  From the above discussion we can deduce that though the initial replacement cost of LED lamp is high but its payback period is only one year. So, for entire next 18-23 years, customers will have benefit of energy saving through bills.

  This will result in reduction of connected load for a given installation, thereby reduction in Maximum Demand on Power system network and Average power requirement. It is necessary at this stage that the lamp manufacturing companies to provide an LED lamp fitting to replace the India’s mostly used 60W incandescent lamp particularly for rural regions.

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Source: http://lightingindia.in/blog/post/id/13954/understanding-relevance-of-led-lamp