An example of the T in the IPAT equation is the luminous efficacy of a lighting device. The visible light output of a light bulb is measured in units of lumens, and theoretically a watt can generate 683 lumens (assuming an ideal monochromatic light source that emits all incoming energy at a specific wavelength in the visible spectrum).

a.) If a 100 watt incandescent bulb generates 1800 lumens, what percentage of maximum efficiency is achieved?

b) Search online for standard LED bulbs by two manufacturers (meaning GE, Phillips, ..., not something being developed at MIT). By how much does the energy efficiency vary between the manufacturers for the same types of bulbs and by how much does it vary between different types of bulbs produced by the same manufacturer? Provide details of the bulbs you compared.

c.) Consider the savings from switching from the 100 W incandescent to the most efficient LED bulb you found in b). Calculate the savings in dollars, per year of operation, per bulb, relative to a 100 watt incandescent bulb, assuming that both bulbs provide 1800 lumens and are used 6 hours per day? Assume that electricity costs $0.20 per kilowatt hour.