My Smarter Essex

Lighting efficiency study

This article is part of a series of follow-up questions on the My Smarter Essex presentations.

Over the years illumination in houses has become more efficient. This has been achieved in three ways:

  1. The light emission medium generates more lumens (light) per watt (unit of power).
  2. The light emission spectrum better matches that of the eye receptors.
  3. The luminaire (the overall fixture) has become more efficient at directing light to its desired place.

We can ignore (2) as most lighting technologies are now pretty well aligned to eye performance. For this exercise, we will also assume that luminaire design has negligible loss due to lenses and/or reflectors and optimal shape, thus neglecting (3).

This gives us a comparison on price, expected life, amount of light and amount of power for the three main current lighting technologies:

  • Light-emitting diode (LED)
  • Compact Fluorescent Lamps (CFL)
  • Traditional incandescent lamps

From we get the following (figures correct as of Summer 2016):





Light bulb projected lifespan

20,000 hours

10,000 hours

1,200 hours

Watts per bulb (equiv. 60 watts)




Cost per bulb




KWh of electricity used over 50,000 hours




Cost of electricity (@ £0.10 per KWh)




Bulbs needed for 50k hours of use




Equivalent 50k hours bulb expense




Total cost for 50k hours




Total cost for 25 bulbs (over 50k hours)




Savings to household (25 bulbs) by switching from incandescent




We've not shown halogen, which is a type of incandescent lamp but slightly more efficient in terms of lumens per watt and much longer-lasting.

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