Configuring LED pitching for optimal design of Luminairies

The lighting business in India is of the order of Rs 13,000 crores. The present installed electrical capacity in India is 250 GW (as on 30.06.2014) and the annual energy generation is 946 billion kWh/year. Lighting load which is accounting for nearly 18% of the total electrical energy (170 billion kWh/year) and 20% in peak (60 GW) during 1800-2100 hours is presently having virtually no digitally controllable component. There are around 280 million households in India in 2012 of which 190 million are in the rural area and 90 million are in the urban area. Nearly 40% of the rural households use kerosene/lighting systems as they are not connected by the electric grid. A small percentage of electrified households also use kerosene lamps. In the urban area nearly 90% of the households use electric power for lighting. Hence there are still 75 million rural households & 9 million urban households which are dependent on kerosene for lighting.

  The challenges facing the emerging technologies in the Indian context are multiple.

• Covering the total lighting needs of the country including total elimination of kerosene lanterns. 
• Change over from the inefficient lighting systems to energy efficient lighting solutions across the country. The change over requires undertaking energy audits which will provide insight into the viability of retrofits & renovation. 
• Facilitating the technology manufacturing base, adoption and absorption of emerging solutions. 
• Developing focus on balance of systems such as day light solutions, reflectors, luminaries, controls and automation. 

  Emerging technologies are those which are not fully in wide scale use and under the developmental process of improvement. The performance measuring metrics such as EMI-EMC compatibility, electrical quality, starting characteristics and equipment life are not fully developed for these.

  The broad areas of emerging technologies are photonics. Photonics are on the way to take the centre stage both as basic energy converters (solar photovoltaics) (SPV) as well as light sources (LEDs). Flexible electronics based on organic systems is the emerging area in photonics.

  Application wise, the most promising emerging technologies appropriate to the Indian needs are AC LED lamps for indoor, semi-outdoor and outdoor lighting and DC led systems powered by solar photovoltaic for portable lighting systems and off grid systems.

Configurations of LEDs for luminaries

  The LEDs are available as single LEDs and the luminaire configuration is built out of the individual LEDs.

  Table 1 gives typical details of power density and total power of luminaries built out of individual LEDs.

  It can be seen that there is a linear relationship between the power, no of luminaries and the area of cross section. The power is given by 0.14 W/cm2. The number of LEDs is given by 5.5 LEDs/100 cm2 after the initial 5 LEDs. However, these configurations are not the optimal configurations and many of these are based on the ease of placement of the LEDs. For optimal pitching of LEDs to obtain the maximum lumen efficiency, the higher LED density in closer proximity gives better lumen efficiency of the luminarie. Ideally, if all the LEDs are located in close pitch the lumen efficiency of the luminare would increase. However, consideration of heat dissipation would dominate the close pitching which would call for sparse pitching. Also the spread requirement of the application calls for sparse pitching.

Fig. 1: give the variation of power of the luminaire and no of LEDs with area

Fig. 2: give the variation of power of the luminaire and no of LEDs with area

Fig. 3: Circular 

Fig. 4: Circular 

Fig. 5: Circular 

Fig. 6: Circular 

Fig. 7: Circular 

Fig.8: Rectangular

Fig.9: Rectangular

Fig.10: Rectangular

Fig.11: Tube light design

Conclusions

In conclusion, it can be said that-

• Ideally dense pitching of LEDs would give the highest lumen efficiency of the luminaire. However, considerations of heat dissipation and light spread requirements of the particular application would call for sparse pitching. 
• Presently designed pitching of LEDs for various applications are far from optimal and the considerations are mostly the placement of these and the heat dispersion. The pitching is not being optimized from the angle of lumen efficiency of the whole system. R&D studies are called for to optimize the pitching for maximum lumen efficiency.

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M Siddhartha Bhatt is Additional Director and Divisional Head of the Energy Efficiency and Renewable Energy Division of cpri, Bangalore. Neha Adhikari is working as Engineering Officer in Energy Efficiency and Renewable Energy Division, CPRI Bangalore. K Pradeep is working as Engineering Assistant in Energy Conservation and Development Division, CPRI, Bangalore.

Source: http://lightingindia.in/blog/post/id/8612/configuring-led-pitching-for-optimal-design-of-luminairies