Dave Plowman wrote:

In article ,
The Natural Philosopher wrote:

Average lightbulb is around 1-2%.efficient. Halogen being at the upper
end, and cheapo dim long lifers at the other.


However the eye perceives brightness logarithmically. To be twice as
brght probably means 4-10 times the power. That makes efficiencty
variations of even 2:1 pretty insignifiocant.


I recently changed the bulbs in my car headlights. Same size. The
difference in light output was *dramatic*.


Wattage probably varied then. I got failed on an MOT for having 'wrong
bulb' in rear lights. I hadn't - just two different brands.



I couldn't give a toss about the theory, but the practice means a great
deal.