LED Downlight Snubber

[AndrewMgan1976]

I am currently replacing 28 tradition ES 100w R80 down lights with 15w LED down lights within a local theatre. These are controlled by a dimmer (which is lets say a little bit old). Job has been going great, light output from the LED is so much better, been dimming the lights as they have been replaced but, today when all LED fittings have been installed, they are not dimming fully.

I know I need a snubber to fix the problem but, I am unsure of how to work out the size required.

At present I have reconnected 6 traditional lamps into the circuit which has reduced the glow but not completely eliminated it.

Thank you in advance.

 

[davesparks]

What dimmer is it they are connected to? I assume we are talking houselights here?

A snubber wont help you I am afraid, LED fittings just wont dim acceptably for use in a theatre when connected to a phase angle control dimmer. They wont dim smoothly or evenly enough to do the job and have a tendancy to snap on and off at the lower end of the dimming curve.
You will have artistic directors and lighting designers out for your blood if they don't dim in exactly the same way as a filament lamp!

Assuming the dimmer is a stage lighting dimmer then the glow you are experiencing at the moment is likely to be due to the preheat current. Stage lighting dimmers (particularly old ones) have a preheat current which just warms the filaments of lamps to improve the length of their life.

 

[AndrewMgan1976]

Yes it is the house lights, they have dimmed down perfectly until the last 8 led fittings have been installed.

Genuinely don't know about the dimmer.

 

[davesparks]

They will do that yes, the last few filament lamps will be effectively acting as a ballast load on the dimmer.

If you don't know what dimmers they are how did you check the minimum load requirements before starting the job? If you haven't checked this out you may not have enough load on there for the dimmer to even start working properly!

 

[davesparks]

I am speaking here as a veteran of having installed 30 LED downlights in an auditorium and then pulled them all out and replaced with GU10's! In theory there was nothing wrong with the setup and they all worked fine when first installed but the blasted things kept failing regularly (replaceing at least 12 every 6 months)
We had tested sample fittings in the space and using the dimmers before hand and in hindsight really should have seen this coming if I had actually though about it all a bit more. LED fittings on a phase angle control dimmer seemed too good to be true, and I should have realised it was.
Using them in a domestic enviroment where you don't need a smooth dimmer curve from 0 to 100% is one thing, theatre is quite another

 

[AndrewMgan1976]

I appreciate your input mate, especially as you have been through it before. I need to check what style of dimmer it is tomorrow.

We have it virtually nullified with the old fittings but even then it is only a temp fix, if one lamp goes, then the led's grow brighter!!

 

[davesparks]

I had the advantage of having worked in theatre and stage lighting since before I started my apprenticeship. When I did that job we were replacing the entire stage lighting installation.

If your system is controlled by regular stage lighting dimmers (houselights often are) then you have to remember each dimmer channel is likely to be rated at at least 2.5KW so is a bit beefier than what most electricians are used to.
Are all of the houselights on one dimmer circuit or are they spread across multiple circuits? Your original load being 2.8KW doesn't really give anything away as these dimmers can easily be rated at 3KW or 5KW.

 

[AndrewMgan1976]

House lights are all on one dimmable circuit.

The system has 3 switches, on, off and preset.

Our new LED load is 420w, so no where near the existing load.

 

[davesparks]

420W would be enough for most dimmers, but if they are of an older type as you suggest they could be thyristor based dimmers rather than triacs and although I don't know as much about them I'm sure they require more minimum load and do have a bit more leakage even when at 0%.

I hope it wasn't you who sold the new lights to the client! cos I think someone's going to have egg on their face over this one.

 

[AndrewMgan1976]

No, I'm ok in the light ordering process.

Could be a fun day tomorrow!

 

[davesparks]

I may be wrong but I can forsee a change of light fittings being the soloution. Unless the ones you have can be fitted with a driver which takes some form of data in and handles the dimming internally, 0-10V control would be ok if the house-light control is independent of the lighting control desk, but if control needs to be via the lighting desk you'll be be getting involved in DMX control at some point