Energy-Efficient Lighting

High performance incandescent lighting

Lighting accounts for 15% of the total electrical consumption in the US, of which incandescent light bulbs (ILB) still account for 30% of the market. While traditional ILB are inefficient - reaching a luminous efficiency of just about 2% as most of the energy is radiated as infrared, they are still often preferred over alternatives because of their low retail price and high color rendering index (CRI). A promising way to improve the efficiency of ILB is to tailor the emitted spectrum using interference filters that reflect the infrared energy back to the filament while transmitting the visible light. This approach has the potential to overcome current LEDs in terms of luminous efficiency while conserving the excellent color rendering index of ILB.

At DRL, we are using a planar tungsten incandescent emitter sandwiched between two interference filters optimized to reflected infrared and transmit visible light for a wide range of angles. The device currently shows up to 50% energy savings and a threefold increase in the visible light output compared to a bare filament consuming an equal amount of power. Although significant energy efficiency improvement has been demonstrated, we are currently investigating (numerically and experimentally) several challenges such as minimizing filament evaporation and filter temperature while maximizing the geometrical view factor and luminous efficiency. We hope that this work will lead to an energy efficient incandescent light source that is also commercially viable.

This work is funded by the Solid State Solar Thermal Energy Conversion Center and is done in collaboration with Professor Marin Soljacic from the Photonics & Modern Electro-Magnetics Group at MIT.