Why does an LED replacement for fluorescent tube start with a delay?

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I had the ballast in an old two tube T12 fluorescent fixture go bad.

The local big box had direct replacement LED tubes on sale, so I tried them
.  They wire directly to line current, no external ballast, but the tubes f
it in the old tombstone connectors.  

They work fine; they start at full brightness even when the room is cold, u
nlike the old fluorescents they replaced.  BUT there is a long delay betwee
n flipping the switch and seeing them start.  It's on the order of 1 - 2 se
conds, I haven't tried measuring yet.  

We've been discussing this on another forum.  Why would there be a delay?  
It's not unique to mine, either, others have noticed similar results.  

Re: Why does an LED replacement for fluorescent tube start with a delay?
On Monday, October 29, 2018 at 9:53:34 AM UTC-4, Tim R wrote:
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em.  They wire directly to line current, no external ballast, but the tubes
 fit in the old tombstone connectors.  
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 unlike the old fluorescents they replaced.  BUT there is a long delay betw
een flipping the switch and seeing them start.  It's on the order of 1 - 2  
seconds, I haven't tried measuring yet.  
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  It's not unique to mine, either, others have noticed similar results.

I picked up some 8' LED bulbs to retrofit the fixtures at my store, and the
y start immediately.  

https://www.amazon.com/CNSUNWAY-LIGHTING-Dual-End-Replacement-Fluorescent/d
p/B06VX4562H/ref=sr_1_3?ie=UTF8&qid15%40821784&sr=8-3&keywords=8%
27+led+flourescent+tube+replacement

 But, they do have an input range between 100 and like 270VAC.  There is so
me sort of circuitry inside that keeps the current consistent as LEDs act a
 lot like zeners when it comes to over-volting them.

Do you have a link to the lamps you bought?

Re: Why does an LED replacement for fluorescent tube start with a delay?
On Monday, October 29, 2018 at 10:07:39 AM UTC-4, John-Del wrote:
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them.  They wire directly to line current, no external ballast, but the tub
es fit in the old tombstone connectors.  
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d, unlike the old fluorescents they replaced.  BUT there is a long delay be
tween flipping the switch and seeing them start.  It's on the order of 1 -  
2 seconds, I haven't tried measuring yet.  
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y?  It's not unique to mine, either, others have noticed similar results.
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hey start immediately.  
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/dp/B06VX4562H/ref=sr_1_3?ie=UTF8&qid15%40821784&sr=8-3&keywords=
8%27+led+flourescent+tube+replacement
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some sort of circuitry inside that keeps the current consistent as LEDs act
 a lot like zeners when it comes to over-volting them.
Quoted text here. Click to load it

That's interesting.  Yours are dual end powered (have to wire to both tombs
tones.)  

Mine are single end 4 foot tubes.  They require a nonshunted tombstone, whi
ch I was lucky enough to already have, but changing them out isn't hard.  T
he power wires go to only one end, and there was plenty of wire there to no
t have to splice.  


Re: Why does an LED replacement for fluorescent tube start with a delay?
On Monday, October 29, 2018 at 6:53:34 AM UTC-7, Tim R wrote:
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em.  They wire directly to line current, no external ballast, but the tubes
 fit in the old tombstone connectors.  

Did you disconnect the ballast inside the fixture, that connects to those o
ld tombstone
connectors?  

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 unlike the old fluorescents they replaced.  BUT there is a long delay betw
een flipping the switch and seeing them start.  It's on the order of 1 - 2  
seconds, I haven't tried measuring yet.  

Either the ballast inside the fixture has a start-cycle, OR there's some ki
nd of switch-off
that operates to prevent a power surge from frying the LEDs.   That protect
ion circuit
can be triggered by the power-on transient, and take a while to reset itsel
f.

Re: Why does an LED replacement for fluorescent tube start with a delay?
On Tuesday, October 30, 2018 at 6:25:47 PM UTC-4, whit3rd wrote:
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them.  They wire directly to line current, no external ballast, but the tub
es fit in the old tombstone connectors.  
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 old tombstone
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Yes.  There were LED tubes available that worked on a ballast, and I consid
ered doing that because it would allow a retreat to fluorescent if I didn't
 like them, or if they became unavailable.  But my ballast was bad, and rep
lacements were expensive.  So I removed it and wired 120VAC directly to the
 tombstones.  

Re: Why does an LED replacement for fluorescent tube start with a delay?
 Tim R wrote:
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** Fluoro tubes are mostly used in commercial lighting and then in quite large numbers. A big inrush surge occurs when switching banks or a whole room full of tubes on - trips breakers, bad news.

  The time delay built into many in LED version is there so the inverter circuitry can ramp up slowly, avoiding the usual brief but large current surge that accompanies the use of magnetic or most electronic ballasts.

 In typical commercial applications, the tubes are switched on only *once* a day, so there is no issue as there might be in domestic use - all the LED bulbs I have seen come instantly on.
  
Some even fade out after switch off, just like an incandescent.  


....  Phil  




Re: Why does an LED replacement for fluorescent tube start with a delay?
Anyway, for LED you don't need aballast.

It is a resonant circuit designed for HPOT generation.

Kill it off and connct the LED directly to the mains '(w/o diodes).

You will have immediate lightning ; it is the ballast which introduces a  
delay.



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Re: Why does an LED replacement for fluorescent tube start with a delay?
On Wednesday, October 31, 2018 at 12:05:24 PM UTC-4, Look165 wrote:
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How many times does OP have to say he wired around the ballast and connecte
d directly to the AC source??  He also said he switched to LEDs because his
 ballast was dead.

Internally, they don't connect the LED string to the AC.  So first there's  
a rectifier, then there's an LED current control circuit of some kind.  The
 time the LED string will be powered up will depend on the controller. O2 M
icro makes a lot of controllers, and I have seen them in many LED TV suppli
es.  There is often a short delay depending on the control IC before the st
ring is powered up.

The 8 footers I have power up almost immediately, but perhaps the controlle
r IC in OP's tubes delay the output until the input filter is fully charged
 by design.  Since LEDs don't put out any significant light until they reac
h close to their run voltage, maybe his controller just ramps up the string
 slower than the one in my 8 foot tubes.

The fact that all his examples do the same tells me it's just the way it's  
designed and not a failure.

And once again, he DISCONNECTED the ballast and wired them directly.

Re: Why does an LED replacement for fluorescent tube start with a delay?
wrote:

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I just replaced some incandescent bulbs with LED bulbs and they have a
delay like the OP describes. The new LED bulbs are the dimmable type.
I wondered if the delay is coming from a cap being charged through a
resistor. They also have an off delay similar to an incandescent. Not
exactly the same but they do dim until almost completey off and then
abruptly turn off all the way.
Eric

Re: Why does an LED replacement for fluorescent tube start with a delay?

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To start the switching control IC needs a 12V supply.
The only low cost way to get it is by slowly charging a capacitor from
rectified mains through a rather big dropping resistor.
After start a special transformer winding takes care of the 12V.
If the LED lamp can be used on both 120/240 VAC start must be much
slower with 120V.
Here in France I never really noticed the problem.
On the other hand,normally off lamps, sometimes blink slowly in the  
dark
because of capacitive coupling of the wiring around the switch.

Re: Why does an LED replacement for fluorescent tube start with a delay?
On Saturday, November 3, 2018 at 2:32:14 PM UTC-4, bilou wrote:
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I have not noticed this, but there is approximately 15 feet (5 meters) of mains wire between the switch on the wall and the light.  

When I lived in Germany many of the light switches were momentaries, and just changed state of the breaker in the panel.  Here in the US I've never seen that done.  The light switch on the wall directly controls the power to the light.  

Re: Why does an LED replacement for fluorescent tube start with a delay?
the cap is useless.

Just make sure you have a rectifyer bridge instead than a simple diode  
as rectifyer.

think od half sine and double sine feed.




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