Hello,

I bought a LED light which claims to be 30W.
It is powered from the main 220V.
Attached is a picture of the power system which seems to bring the 220V to what seems like 2x100V channels. (as measured with a multimeter between the middle and side wires).

What I need to do is reduce the LED brightness by a factor of 10 or 100 (I want to use it to callibrate a telescope camera, which are hyper senstive).

What would be the best way to do it?

I first thought about adding a resistor in series, but I have no clue what spec to use for the resistor.
I also thought that the voltage regujlators probably have a "tunning" resistor and that "simply" swapping out a small smt component might reduce the overall power, but I have no clue which one it will be and by what I need to change it... And that is befre talking about the dificulty of doing the soldering!

Can you guys help me find the best/easiest sollution?

Thanks,
Cyrille

 

Buy neutral density gel filter and wrap the lamp.
You will find fiddling with the electronics yields poor results- color temperature shifts, etc.

So easy.

 

Your photo isn't very high quality, so it's hard to tell which resistors set the current through the LEDs. The resistors that determine the current are small, usually up to 10 ohms or less. It could be that it's resistor R1, R1A and R2, R2A. I'm guessing that R1 and R1A are connected in parallel, and also R2 and R2A .Insert another resistor, slightly higher in resistance, and you'll see if the LED brightness has decreased

 

Hello,

Thanks,

I take it cutting the "middle" wire, adding a resistor in series there is not a good idea?

Note that in typical use, the light will be turned on for around 1 minute per night..
Color temperature is not an issue also.

I was able to take these 2 slightly better pictures of these resistors.

Thanks
Cyrille

 

Buy neutral density gel filter and wrap the lamp.
You will find fiddling with the electronics yields poor results- color temperature shifts, etc.

Exactly this….

 

I also thought that the voltage regujlators probably have a "tunning" resistor and that "simply" swapping out a small smt component might reduce the overall power, but I have no clue which one it will be and by what I need to change it... And that is befre talking about the dificulty of doing the soldering!

Сurrent of LEDs is defined by value of parallel connected feedback resistors R1 and R1A (R2 and R2A).
Bigger value - lower current - bright reduced.

ADDED:
To @Pyrex : Sorry, i did not notice your post #3.

 

Hello,

Thanks,

I take it cutting the "middle" wire, adding a resistor in series there is not a good idea?

Note that in typical use, the light will be turned on for around 1 minute per night..
Color temperature is not an issue also.

I was able to take these 2 slightly better pictures of these resistors.

Thanks
Cyrille

sure you can add a resistor in series with those two

 

Hello,

Do you have proposal on values and specs of the resistance?

Cyrille

 

Hello,

Do you have proposal on values and specs of the resistance?

Cyrille

take a resistor with about twice the nominal value than the previous one

 

Try sending the photo to Big Clive (YouTube). He has a hobby of LED lighting and enjoys modifying the PS circuits to reduce the output to the LEDs. Seriously.

The fastest way to get his attention would be to pay the two bucks to join his Patreon and message him there.

 

Thanks, will try!

 

Since I don't see any circuit schematic of that PCB, nor any information as to the "30 watt lamp", nor about the connections, providing detailed advice is a serious challenge.
What I think is that there are actually two LED light sources that we are not shown or told about.
IF the TS is able to accurately measure the voltage from the center positive terminal to each of the two side(negative) terminals, then we can guess the current on each side, and suggest a suitable series resistor to add to reduce the light intensity.
The data in the link attached to post #6 was quite helpful. BUT what I see of that circuit tells me that adjusting it by changing a resistor will not be as simple as we would like it to be.

A description of the LEDs portion of the light package assembly will serve to help with suggestions as to how to make changes.
AND I am wondering what sort of light would be used " to callibrate a telescope camera, which are hyper senstive). "
My guess is a lot less than 30 watts.

 

I bought a LED light which claims to be 30W.
...
What I need to do is reduce the LED brightness by a factor of 10 or 100 (I want to use it to callibrate a telescope camera, which are hyper senstive).

What would be the best way to do it?

Buy a different, dimmable LED with a much lower output. You're trying to swat a mosquito with a sledge hammer. Just start with the right tool for the job and save yourself the trouble.

 

Highly doubt the circuit is "tunable" using resistors to achieve 10x less output. Let alone 100x.

Are you really sure it's 100V DC and not something coming from the mains side?
You could spend a few dollars Aliexpress to get a DC PWM controller with enough voltage input.