[HH] How much do LEDs dim over time?

[Jerry Feldman]

While I don't have empirical evidence, a friend of mine replaced all the
lights in his office (was 100% fluorescent) and his kitchen at home. He
was bragging on how much lower his power bill was, and that the LED
light was much better for his employees to see with. I'll give him a
call and see if the lighting in his office is still pretty good.

On 02/01/2013 06:10 PM, Tom Metro wrote:
> How much do LEDs dim over time? A hacker (Bogdan Raducanu, an EE
> student) set out to measure it. (Link via @dangerousproto,
> https://twitter.com/dangerousproto)
>
> http://www.electrobob.com/led-logger/
>
>   One important aspect that comes to mind is about the lifetime of [LED
>   strips], are they better than bulbs, overall? Obviously there's no
>   specification you can trust anywhere. So, how do I know if cheap
>   strips are good enough or it is worth spending the money on more
>   expensive ones? Measure some data for the cheap ones and see if they
>   are good enough.
>
>   I setup a very simple device, for first measurement attempt: a metal
>   project box houses 15 cm of unused strip that shines light on a
>   TLS2550 sensor, everything being isolated from ambient light.
>
>   This sensor is really great: it has I2C interface, high dynamic range
>   and approximates the human eye response, giving the result directly in
>   lux (after some math). I've used a microcontroller and an EEPROM
>   memory with a couple of years of space, storing data every 6 hours.
>   ... The used board is Arduino compatible, but it was not used with the
>   Arduino environment, just your regular C.
>
>   The light has been on continuously for 1400 hours, two months. ... So
>   far, the LED strip has dropped about 18% in brightness compared to the
>   beginning. Current has stayed the same, meaning that they are actually
>   reducing their efficiency.
>
>   I decided to try to predict the life of the LEDs. Since they don't
>   burn but rather fade, I think that the point where they dropped to 70%
>   of initial intensity is a good mark of their end of life in
>   applications where they are used for lighting and not decoration.
>
>   Using an exponential projection I found that it will take just 2200
>   hours until the LEDs drop to 70% of their initial intensity. This is
>   rather disappointing, even for cheap LEDs.
>
> See link for the graph.
>
> The author goes on to do some comparisons of the light output and power
> efficiency of the cheap LED strips he is using with fluorescent and
> incandescent lights, and do a cost comparison, given the projected life
> span of the LEDs.
>
>
> It's long since been well known that fluorescent backlights on LCD
> displays significantly diminish in brightness over time, but I wasn't
> aware that LEDs had the same problem, to that extent, even if less
> pronounced. I thought consistent light output (and power savings) was
> one of the big reasons for switching to LED backlights.
>
> So that means our household bulbs that have been upgraded to LEDs with
> supposed 100,000 hour/20-year lifespans will likely need to be replaced
> far sooner due to diminished output?
>
>
> The author also has a good posting collecting the common power supply
> circuits for driving LEDs with a decent explanation of the theory behind
> each:
> http://www.electrobob.com/linear-led-power-supplies/
>
>  -Tom
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>


-- 
Jerry Feldman <gaf at blu.org>
Boston Linux and Unix
PGP key id:3BC1EB90 
PGP Key fingerprint: 49E2 C52A FC5A A31F 8D66  C0AF 7CEA 30FC 3BC1 EB90


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