Switching off lights

[Heptagon]

Can anyone give advice on the question of switching off led luminaires?

 

 

I have heard that they should be left switched on - to keep the fans running until they cool down, but I can't understand this.

The bulk of the heat generation when they are running has to be from the LED, and as soon as they are switched off, that stops.

So the LED must start cooling immediately - so it can't possibly cook itself.

What else can get cooked? - given that no other circuits are powered up.

(Simple thermodynamics - "you can't take heat from the cooler to the hotter - you can try if you like but you're much better notter").

 

Our venue has a "leave it on" policy, and the luminaire fans are running 24/7. Also the luminaires are blowing out at an amazing rate.

All our luminaires doco advise to switch off when not in use.

 

Any solid info available?

[adam2]

I would say turn off when not in use. A little electricity is saved thus, and also the fan is often the weak point in such equipment and running it 24/7 will only shorten the life of the fan, and also suck in more dirt and dust.

[Jivemaster]

The dust that the fans and vent passages accumulate will rapidly cause the luminaires to die when running. If the instructions say switch off when not in use that's what you should do but if your management say leave on then that's what you must do.

 

I once heard that leaving projectors on was best, then I went into a school hall where the projectors were left on for the summer holiday!

[Junior8]

There used to be all sorts of 'advice' about leaving items switched on most of which I always suspected was poppycock. I never followed any of it and don't recall any problems. My view has always been that equipment should be left running only when it needs to be in use - and if there was a need for s shut down procedure it would be specified. As usual, as you say, Flanders and Swann had it right. I can't see why the fan would be needed to keep cool things cool. Edited June 21, 2021 by Junior8

[Stuart91]

I once heard that leaving projectors on was best, then I went into a school hall where the projectors were left on for the summer holiday!

 

Most projectors need powered down via the button on the unit (or remote) before the mains is cut. This allows the fans to keeping running for a while, without that airflow over the lamp it can overheat and sustain damage. Each time the lamp strikes, a little more lifespan is taken off it, so it'd be sensible to leave the projector on over, say, a 15 min interval break.

 

I imagine similarly well-intentioned advice was garbled as it percolated through the school. Wouldn't like to have seen the bill for replacing all the lamps after the summer break.

[sandall]

There used to be all sorts of 'advice' about leaving items switched on most of which I always suspected was poppycock.

Back in the day job we found that edit suite breakdowns went away once we started leaving the computers on 24/7, & in general older dimmer racks tend to give far less problems if left on.

 

Most projectors need powered down via the button on the unit (or remote) before the mains is cut.

Some projectors have a battery or capacitor backup for the fan, so if you pull the mains the fan keeps running for a while (an attempt at idiot-proofing?)

[Stuart91]

Some projectors have a battery or capacitor backup for the fan, so if you pull the mains the fan keeps running for a while (an attempt at idiot-proofing?)

 

I haven't come across that myself, but it seems like a very good idea.

[sandall]

Some projectors have a battery or capacitor backup for the fan, so if you pull the mains the fan keeps running for a while (an attempt at idiot-proofing?)

I haven't come across that myself, but it seems like a very good idea.

I "inherited" a Panasonic which does it - excellent for dry hire, where proper shutdown by the customer is but a dream. Don't know how widespread it is, but definitely something to look for.

[Jivemaster]

I don't think there is solid advice applicable to all luminaires (etc) Personally I'd switch things off if the shut down is for an hour or more.

[Jivemaster]

The problem with fans left on is that they rapidly collect dust and smoke residue and then move less air til things than get hot, get too hot and die.

[bruce]

The problem with fans left on is that they rapidly collect dust and smoke residue and then move less air til things than get hot, get too hot and die.

There's also the opposite situation - although not really relevant in this scenario.

 

I manage an environment that has around a thousand devices (network switches) which run 24x7. Many will have been powered on for several years continually. The fans have been running continuously. If they are powered off and back on some time later, it's not uncommon to get "stiction" in the bearings as they cool, and the fans don't start turning again. Give 'em a tap, and they'll run happily for another couple of years.

 

There was one particular model of equipment that was prone to this, and we had hundreds of them. If we ever had a power cut, when power was restored most of the systems would restart just fine. But we'd then start getting failures later, as some fans would have failed, and the PSUs cook themselves after a few hours or days.

[dje]

The problem with fans left on is that they rapidly collect dust and smoke residue and then move less air til things than get hot, get too hot and die.

There's also the opposite situation - although not really relevant in this scenario.

 

I manage an environment that has around a thousand devices (network switches) which run 24x7. Many will have been powered on for several years continually. The fans have been running continuously. If they are powered off and back on some time later, it's not uncommon to get "stiction" in the bearings as they cool, and the fans don't start turning again. Give 'em a tap, and they'll run happily for another couple of years.

 

There was one particular model of equipment that was prone to this, and we had hundreds of them. If we ever had a power cut, when power was restored most of the systems would restart just fine. But we'd then start getting failures later, as some fans would have failed, and the PSUs cook themselves after a few hours or days.

 

I did some work programming industrial automation last year - 6-axis 3D milling robots mainly, and some flatbeds, some of these robots are switched on for a year at a time and produce components completely autonomously. (Yeah it's kinda scary seeing a robot flinging around a high speed cutter on a spindle completely of its own accord). Some of the really critical cabinets have optical sensors on the fans so that the sensor can decide if the fan is running or not, which in combination with the temperature sensor inside, can help the PLC decide if there's a problem or not, and advise the operator if somebody needs to go give it a nudge.

 

Yes - in due course I'll add a little servo so the PLC can kickstart the motor itself!

[bruce]

yeah, modern kit will have sensors on fans which tell you if things fail. Older kit didn't.

 

Like the idea of a little servo to kick the fan back into life :)

 

Getting way way off topic now, but I remember many years ago buying a very expensive tape backup device for an IT system. They used Exabyte tapes, which were mechanically similar to the 8mm cassettes used at the time in camcorders etc.

 

We had dozens of "shoebox-size" exabyte drives, attached to servers. Someone spent hours each day changing tapes.

 

But this one was an "exabyte jukebox" - which had one drive, and held a couple of dozen tapes, so much more capacity. You could tell it "eject current tape, and insert tape 11".

 

We opened it up and had a look, expecting some clever integration between the tape drive and juke box mechanism. Inside was a standard Exabyte drive, and some meccano-like jukebox machine. When you told it to change tapes, there was a robot finger that moved forward and pressed the normal "eject" button and then the meccano grabbed the cassette when it popped out and changed it....

[Heptagon]

yeah, modern kit will have sensors on fans which tell you if things fail. Older kit didn't.

 

Like the idea of a little servo to kick the fan back into life :)

 

Getting way way off topic now, but I remember many years ago buying a very expensive tape backup device for an IT system. They used Exabyte tapes, which were mechanically similar to the 8mm cassettes used at the time in camcorders etc.

 

We had dozens of "shoebox-size" exabyte drives, attached to servers. Someone spent hours each day changing tapes.

 

But this one was an "exabyte jukebox" - which had one drive, and held a couple of dozen tapes, so much more capacity. You could tell it "eject current tape, and insert tape 11".

 

We opened it up and had a look, expecting some clever integration between the tape drive and juke box mechanism. Inside was a standard Exabyte drive, and some meccano-like jukebox machine. When you told it to change tapes, there was a robot finger that moved forward and pressed the normal "eject" button and then the meccano grabbed the cassette when it popped out and changed it....

 

I've seen some other plans by this designer - one Heath Robinson