My comparison of the brightness of different kinds of light-bulb.

Two days ago I tweeted a contribution to the upcoming 10:10 forum on LED lighting:

@1010 We have two LED bulbs billed as 60W replacements by Homebase which are much brighter than 100W

When this provoked some interest I added that I had kept meaning to test this impression by using the light meter of my camera.  10:10 replied that they would be interested in the results. So, waiting only for darkness to descend, I went ahead with my simple experiment. Which confirmed my assertion, thus:

Method:

Setup

Lumix G2 camera set on Aperture Priority mode.  Sensitivity at ASA 1600  Aperture fixed at f3.6

Night time. No other light sources present.

The only change made between each reading was the  bulb itself.

The two mini fluorescent examples were allowed to warm up to full intensity before taking their readings.

Results:

• 60 Watt Incandescent:      1/60th second exposure required*
• 100 Watt Incandescent:    1/100th second exposure required*
• 15 Watt mini-fluorescent:   1/100th second exposure required*
• 12 Watt LED:   1/160th second exposure required*
• 30 Watt mini-fluorescent:   1/200th second exposure required*

*The amount of light produced by the bulb is presumably in inverse proportion to the length of the exposure required – i.e. the shorter the exposure the brighter the bulb.

Conclusion:

These results suggest that while the 30W mini-fluorescent is the brightest bulb tested, the 12 Watt LED bulb bought from Homebase produces nearly three times as much light as the 60 Watt incandescent bulb for which it was billed as a replacement, and is more than half as bright again as the 100 Watt example, just as I claimed in my tweet.

Discussion:

One factor inhibiting people from changing over to LED lighting in their homes (apart from the cost – which is falling dramatically) is the belief that you can’t really get an adequate replacement for a standard 100Watt light bulb. Homebase, at least, appears to be contributing to this misconception by underselling the particular LED bulb which I used in this comparison.

I had no means of testing the accuracy of the wattage marked on the different bulbs, but if these are roughly correct then this experiment also supports the commonly repeated claim that LED bulbs use approximately 1/10th the electricity for the same light output.

I can feel further blogs coming on re:

• The emerging practicality of large-scale changeover to much more efficient means of domestic lighting
• The enduring validity of amateur experimentation, even in cutting-edge areas.