What did you do to your Z this week?

[AliK]

I wish I understood the above ...
Oh, and nothing.

Sorry, that was arrogant of me to write it that way.

Put another way, a classic filament bulb starts to heat up and emit light as you apply voltage / current and gets brighter as you turn up the voltage (proportionally).

An LED works on a totally different principle of electrons "jumping orbits" and "falling down again" - the energy loss between the "orbits" is emitted as light. So, an LED emits no light typically under 1.2-1.4v; at which point it "turns on" (imagine it's at the bottom of a hockey stick and climbs rapidly). From that point on, if you increase voltage, it gets to it's max brightness VERY quickly and doesn't get noticeably brighter by applying more voltage say above 5-6v.

The curve between the bottom of the hockey stick and the bottom of the handle is what is called the quiescent point where varying the voltage (say between 1.4v and 3v) will result in varying degrees of brightness akin to a normal light bulb.

The Pulse Width Modulation (PWM) dimmers turn an LED on/off hundreds of times a second and vary the duration of how long it is On for. This has the effect of tricking your eyes into seeing a dimmer led. But some people like me have eyes that are sensitive to this and see flicker or a disco light strobe effect. Imagine someone wearing white gloves and moving their hands in a disco with a strobe light. That's what I see with the modern rear cluster LED lights in traffic when I move my eyes (or indeed any LED dimmed using PWM).

 

[Russell]

Sorry, that was arrogant of me to write it that way.

Put another way, a classic filament bulb starts to heat up and emit light as you apply voltage / current and gets brighter as you turn up the voltage (proportionally).

An LED works on a totally different principle of electrons "jumping orbits" and "falling down again" - the energy loss between the "orbits" is emitted as light. So, an LED emits no light typically under 1.2-1.4v; at which point it "turns on" (imagine it's at the bottom of a hockey stick and climbs rapidly). From that point on, if you increase voltage, it gets to it's max brightness VERY quickly and doesn't get noticeably brighter by applying more voltage say above 5-6v.

The curve between the bottom of the hockey stick and the bottom of the handle is what is called the quiescent point where varying the voltage (say between 1.4v and 3v) will result in varying degrees of brightness akin to a normal light bulb.

The Pulse Width Modulation (PWM) dimmers turn an LED on/off hundreds of times a second and vary the duration of how long it is On for. This has the effect of tricking your eyes into seeing a dimmer led. But some people like me have eyes that are sensitive to this and see flicker or a disco light strobe effect. Imagine someone wearing white gloves and moving their hands in a disco with a strobe light. That's what I see with the modern rear cluster LED lights in traffic when I move my eyes (or indeed any LED dimmed using PWM).

Ali - Not thought about doing it this way as PWM is the generally accepted way of doing things. My eyes arent sensitive to it but I remember when Cathode ray TV's were about I could hear the high pitched buzzing from many rooms away.

Anyway on to my point. Your method will only work should you not want to dim down too far. As you mentioned, an LED will go from OFF to ON at a set voltage which gives you your minimum brightness. If im not mistaken, you would have a really small adjustment margin?

 

[Paul_S]

Great explanation of LEDs. That's why they appear to strobe and sometimes 'dance around' when you see a slow motion shot of a car on TV.

 

[AliK]

Ali - Not thought about doing it this way as PWM is the generally accepted way of doing things. My eyes arent sensitive to it but I remember when Cathode ray TV's were about I could hear the high pitched buzzing from many rooms away.

Anyway on to my point. Your method will only work should you not want to dim down too far. As you mentioned, an LED will go from OFF to ON at a set voltage which gives you your minimum brightness. If im not mistaken, you would have a really small adjustment margin?

And you're spot on there fella. Having done this type of circuit before I spent an age getting the range on the pot just right. Oh and then there is blocking noise and ripple to avoid unwanted fluctuations. As you well know it's a faff hence not done it yet [emoji6]

I totally understand your thing on the CRT screens - I used to get that too. But with my new engine and exhaust, I'm rapidly reducing my hearing range [emoji13] [emoji14]

 

[Russell]

And you're spot on there fella. Having done this type of circuit before I spent an age getting the range on the pot just right. Oh and then there is blocking noise and ripple to avoid unwanted fluctuations. As you well know it's a faff hence not done it yet [emoji6]

I totally understand your thing on the CRT screens - I used to get that too. But with my new engine and exhaust, I'm rapidly reducing my hearing range [emoji13] [emoji14]

Here is your theory in action.

Disposable Chinese special LED

Comes on around 2.4V very dimly

Quickly gains brightness

Maximum brightness around 3v

Anything past that and it dies out a bit.

Starts drawing current as the voltage increases.

Finally popped around 7V.

Hardly a scientific test as everything is cheap Chinese specials but shows the tiny range you have to play with this method.


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[AliK]

Just LOVE the fact that you did that little experiment!!! [emoji106][emoji106][emoji106]

 

[Russell]

Just LOVE the fact that you did that little experiment!!! [emoji106][emoji106][emoji106]

Was meant to be tidying the house ready for estate agent photos tomorrow.
I think it’s called procrastination!




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[AliK]

Fixed my broken engine inspection lamp using kiddies' suncreme lid!!

Will do a proper write up another day!

 

[Russell]

Fixed my broken engine inspection lamp using kiddies' suncreme lid!!

Will do a proper write up another day!

Does the light shine through it?


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[AliK]

Yep, plenty o'light!

I did a proof of concept a few weeks back without cutting it to size. Sadly pics taken in daylight, but you see the off to on difference....

 

[toopy]

Took the rear brakes apart to check and clean up over a week ago, havent had the willpower to reassemble anything, as after working in the heat most of the day each day for work, I can't be arsed to get on with it in the evenings!

 

[Alphabettispaghetti]

Yep, plenty o'light!

I did a proof of concept a few weeks back without cutting it to size. Sadly pics taken in daylight, but you see the off to on difference....

Have you thought about using a lower factor suncream lid to let more light through?

 

[AliK]

Took the rear brakes apart to check and clean up over a week ago, havent had the willpower to reassemble anything, as after working in the heat most of the day each day for work, I can't be arsed

View attachment 29963

I need to do that too and replace the shoes/springs etc - been putting it off for two years now

Maybe next week!!!!

 

[toopy]

I need to do that too and replace the shoes/springs etc - been putting it off for two years now

Maybe next week!!!!

If you havent already got the shoes, check what ones you have first, as i initially ordered the wrong ones, so have a set going spare if you need!

 

[AliK]

Thanks buddy, will let you know!

 

[AliK]

Got a VERY nice surprise in the post today from the DVLA without even applying for it!

Are they automating the process I wonder!?

 

[AliK]

The DVLA aren't failing to impress me of late!!

 

[Pete]

Today I am mainly hanging my steering wheel by the boss till it becomes shiny.

 

[jonbills]

Does hanging by the boss make them shiny? I wonder if it would work for the US of A.

 

[richiep]

Fixed my broken engine inspection lamp using kiddies' suncreme lid!!

Will do a proper write up another day!

What brand of sun cream? Might have one lying around and I have a lamp for the project car that needs a new lens!