Can i dim an led this way

[collectors]

Hi, i am building some signals with a red & green led via a relay & with the test looks fine in the day, but way to bright at night. Now i am very limited with space "IE: a 10mm tube" So i thought a photocell & an extra resistor. Would this work ?? & should the relays be of a different value. Thanks

[End2end]

Why not just increase the value of the resistors in the plan rather than trying to add an/other(s)?
This would do any with the need for the photocell, unless that's in the circuit for another specific reason.
Thanks
End2end

[collectors]

Why not just increase the value of the resistors in the plan rather than trying to add an/other(s)?
This would do any with the need for the photocell, unless that's in the circuit for another specific reason.
Thanks
End2end

Because i wont be able to see the led's in the day light as a few are 25met away.

[Richard08]

Why not just increase the value of the resistors in the plan rather than trying to add an/other(s)?
This would do any with the need for the photocell, unless that's in the circuit for another specific reason.
Thanks
End2end

Because i wont be able to see the led's in the day light as a few are 25met away.

Perhaps put a suitable resistor, switchable day/night, at the supply for the whole circuit(s). It might need to be quite chunky (power rating) to handle the load. Or even a variable resistor?

[RAF96]

I used to control my station and street lighting from the controlled output (speed knob) of an old HM2000 controller. Twiddle the knob and dim the lights.

[collectors]

I used to control my station and street lighting from the controlled output (speed knob) of an old HM2000 controller. Twiddle the knob and dim the lights.

OK, i should of explained i little better. There will be around 20 of these around the garden layout being fed from at least 4 different power supply's & didn't want to have to go around to each signal adjusting the output. I could of put a simple transited/resister & a 10k trim pot on each one if i could. But dont have the room in a 10mm tube in the garden with possibility of the rain.

[Richard08]

Maybe use a light sensor to automatically switch in/out a resistor on each of the four power supplies, a once only job. Must be simpler that trying to modify 20 signals?

[collectors]

Hi, i appreciate all the suggestions, but wont work for far to many reasons in my situation. Is all i was asking, is will what i am suggesting with a photocell & an extra resistor work as per diagram.
1. Cant put any pot or similar because i have other items running off the 5v
2. I am very limited with space "10mm"
3. I am not modifying anything & building from scratch.

Thanks.

[Bufferstop]

LEDs don't respond in a linear manner to restricting the current. Dropping the voltage by putting one or more diodes in series with them will give better results. I'd build an experimental rig where you can test different LEDs with a string of diodes, shorting them out or moving a connecting clip along the string..