[TowerTalk] [Bulk] Re: LED replacement for incandescent light

Wed Jan 14 22:49:29 EST 2015

If lamps are in parallel so any one is sufficient and they are repaired 
then the MTBF goes up a huge amount.  The probability of a surviving 
lamp failing while the burned out one is being replaced is then the 
concern.  For two 1 year MTBF lamps in parallel and a one day repair 
time the math works out to about 183 years MTBF for both failed at the 
same time.  This math is based on steady state failure rates so ignores 
infant mortality and wear out failures, but is illustrative of how 
reliable parallel redundancy can be when prompt repairs are possible.   
However, since filament lamps have finite lifetimes, I think best 
practice would be to burn them in to weed out infant mortality and 
replace both lamps when one burns out.

Ar redundant system familiar to many computer users is the RAID array, 
where the high MTBF is based on a failed drive being replaced promptly.

Grant KZ1W
ref: "System Reliability Engineering", Gerald Sandler

On 1/14/2015 6:02 PM, Patrick Greenlee wrote:
> A constant current source in series would make every in-line series 
> lamp a separate single point of failure which would make the MTBF 1/n 
> times the MTBF of one lamp where n is the number of lamps. Not a high 
> reliability approach.
>
> Patrick   NJ5G
>
>
> On 1/14/2015 1:59 PM, Jim Lux wrote:
>> On 1/14/15 11:52 AM, Jack Brindle wrote:
>>> LED bulbs have power supplies which convert 120/240VAC down to 
>>> thecyDC level needed by the LEDs. These components are the major 
>>> failure point (for CFLs as well). These are high current power 
>>> supplies that generate quite a bit of heat and thus require at least 
>>> some of that heat sink capacity as well.
>>>
>>
>> True for replacement bulbs for replacing standard Edison base 
>> incandescent, like the ones you get at home depot.
>>
>> Not necessarily true for a specialized application.  If you were 
>> replacing ALL the bulbs in a tower, there's nothing stopping you from 
>> having a big constant current source at the base, like they do with 
>> streetlights.
>>
>> It's sort of like replacing incandescents with strobes..
>>
>>
>>
>>> So what kind of climbing harness is required when changing the 
>>> external aircraft bulb at altitude??? :-)
>>>
>>> - Jack B, W6FB
>>>
>>>> On Jan 14, 2015, at 10:55 AM, Hans Hammarquist via TowerTalk 
>>>> <towertalk at contesting.com> wrote:
>>>>
>>>> Replacing a bulb on an aircraft is 'slightly" easier than climbing 
>>>> 1500 feet.
>>>>
>>>>
>>>> Regarding temperature; the LED do not suffer as for example the 
>>>> florescent lights. If I remember it right LE-s work better at lower 
>>>> temperatures, the light output goes down as the temperature 
>>>> increases. You notice that LED bulbs are equipped with rather large 
>>>> heat sinks, needed to keep the LED diodes to work properly.
>>>>
>>>>
>>>> Hans - N2JFS
>>>>
>>>>
>>>>
>>>> -----Original Message-----
>>>> From: Roger (K8RI) on TT <K8RI-on-TowerTalk at tm.net>
>>>> To: towertalk <towertalk at contesting.com>
>>>> Sent: Tue, Jan 13, 2015 5:16 pm
>>>> Subject: Re: [TowerTalk] Fwd:  Now THIS is a tower climb!
>>>>
>>>>
>>>> There already are, very bright LED strobes in use on aircraft.  All 
>>>> the
>>>> exterior lights on mine were solid state, except for the landing 
>>>> light.
>>>> There are LEDs that could have replaced that, but I never saw any that
>>>> had been approved.
>>>> I don't know at how low a temperature they will still function, but I
>>>> flew in temperatures a lot colder than most towers would see.
>>>>
>>>> I would think the new LED strobes would be ideal for towers and
>>>> replacements would be few and far between.
>>>>
>>>> 73
>>>>
>>>> Roger (K8RI)
>>>>
>>>> On 1/13/2015 12:25 PM, Hans Hammarquist via TowerTalk wrote:
>>>>> I think the problem is to introduce a "new", long-life, light 
>>>>> bulb. Any,
>>>> modern LED bulb would do lifetime wise. I believe, though, there 
>>>> are several
>>>> light bulbs in the assembly that automatically replace the bulbs as 
>>>> they burn
>>>> out. That is used in lighthouses to insure there is a light on all 
>>>> the time. To
>>>> design an assembly that could automatically replace burnt-out LED 
>>>> bulbs might
>>>> not be that simple. You know, everything there has to be approved by
>>>> authorities.
>>>>>
>>>>>
>>>>> Hans - N2JFS
>>>>>
>>>>>
>>>>>
>>>>> -----Original Message-----
>>>>> From: Richard Solomon <dickw1ksz at gmail.com>
>>>>> To: Tower Talk <towertalk at contesting.com>
>>>>> Sent: Mon, Jan 12, 2015 6:39 pm
>>>>> Subject: Re: [TowerTalk] Now THIS is a tower climb!
>>>>>
>>>>>
>>>>> Repairs ??
>>>>>
>>>>> Looks like he's changing a light bulb !!
>>>>>
>>>>> Now, invent a really long life bulb and you will sell at least a 
>>>>> hundred !!
>>>>>
>>>>> 73, Dick, W1KSZ
>>>>>
>>>>> On Mon, Jan 12, 2015 at 4:33 PM, Mike via TowerTalk <
>>>>> towertalk at contesting.com> wrote:
>>>>>
>>>>>> This is video of a technician climbing 1768 feet to the top of a
>>>>>> transmissions tower for repairs.
>>>>>>
>>>>>> It also shows him free climbing and some dialog to go along with  
>>>>>> it.
>>>>>>
>>>>>> Its a helmet cam so if anyone gets dizzy or has anything that can 
>>>>>> give  out
>>>>>> watching this stuff while sitting in your chair....be 
>>>>>> warned!...DO NOT
>>>>>> WATCH IT!!
>>>>>>
>>>>>>
>>>>>>
>>>>>> https://www.youtube.com/watch?v=INbKYq0G9nU
>>>>>>
>>>>>> Mike W2GR
>>>>>> _______________________________________________
>>>
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>>
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