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View Full Version : OT? Fluorescent Shop Light Mounting Question



Paul Alciatore
12-31-2009, 10:17 PM
I bought and am installing some inexpensive shop lights. Two tube fluorescents that have an AC cord with standard plug and provision for hanging with chains. I have a ceiling that is only slightly over 8 foot and plan to install them directly on the ceiling (dry wall, aka gypsum board). The instructions state they should be at least 3" from the ceiling with no reason why. I just love that.

Anyone know why they specify that. Is it some kind of minimum hanging distance for the chains, or is there some non apparent safety concern?

Carld
12-31-2009, 10:24 PM
It's in case the ballasts go POOF and let out the magic smoke and start a fire. You could put a fire proof plate behind them I suppose. I have mounted them directly on the ceiling and never had a problem but I never left the lights on in the shop when I wasn't there. I use incandescent bulbs now.

Ken_Shea
12-31-2009, 10:31 PM
It's in case the ballasts go POOF and let out the magic smoke and start a fire. You could put a fire proof plate behind them I suppose. I have mounted them directly on the ceiling and never had a problem but I never left the lights on in the shop when I wasn't there. I use incandescent bulbs now.

That's exactly right, and they will do just that, usually you can smell them giving up the ghost though, presuming you are around, I never leave them on unattended for any length of time. Saves energy too if you are gone for even 10 minutes.

J Tiers
12-31-2009, 11:57 PM
I like hanging them, so that I can tilt the reflector away from me. That cuts glare, and puts more light on the machine/workbench/wall of shelves vs having it shining in my eyes as I work.

oldtiffie
01-01-2010, 12:21 AM
I bought and am installing some inexpensive shop lights. Two tube fluorescents that have an AC cord with standard plug and provision for hanging with chains. I have a ceiling that is only slightly over 8 foot and plan to install them directly on the ceiling (dry wall, aka gypsum board). The instructions state they should be at least 3" from the ceiling with no reason why. I just love that.

Anyone know why they specify that. Is it some kind of minimum hanging distance for the chains, or is there some non apparent safety concern?

Air gap for heat dispersion/dissipation and/or ventilation?

jnissen
01-01-2010, 02:43 AM
I use the 8 foot variety and they can be mounted flush to the ceiling. Lots of light and they last a long time.

winchman
01-01-2010, 04:17 AM
The airplane maintenance shop I worked in had 8-foot fixtures mounted directly to the wooden trusses. When one of the ballasts failed, it got hot enough to ignite the wood, and that got our attention. We never smelled the stuff oozing out of the ballast and collecting in the fixture.

There was an airplane on jacks under the fire, so I climbed up into the overhead with a fire extinguisher to put out the small fire and disconnect the fixture.

Roger

914Wilhelm
01-01-2010, 04:55 AM
It's in case the ballasts go POOF and let out the magic smoke and start a fire. You could put a fire proof plate behind them I suppose. I have mounted them directly on the ceiling and never had a problem but I never left the lights on in the shop when I wasn't there. I use incandescent bulbs now.

The gov'mnt gonna bring that to and end soon enuf. Too bad they want us to use only these energy savings stuff with all the bad juju (mercury, etc)they contain. My only beefs with the florescents is the noise they sometimes put out, the slow time to put out adequate light in my ice cold shop and the strobing I get on my rotaing machinery.

John Stevenson
01-01-2010, 07:33 AM
Do you actually get strobing on rotating machinery? I know in theory it's possible but without repeating parrot fashion from what they have read, does anyone manage to see a stopped piece of equipment ?

The reason I ask is I have tried to reproduce this running variable speed lathes on a bench under a low florry essence light and I can't get it to work.

I know about those small lights on record decks that stop the marks so you know you are on 33 and a 1/3 but they are right next to it, not 7 bloody foot away.

At the piano company I worked at we had to hand grind small drill and cutters down to less than 0.050" to assist us they bought a powerful lab strobe lamp that could 'stop' the wheel so it made grinding easier. Once we bought a Christian drill grinder this fell into disuse.

After I left I had to machines some bearing bores in some deep skeletal motor housings and the view of the boring bar thru the slots was very off putting and hard to see when at speed.

I asked to borrow the strobe and was given it, I still have it, set up at 12 "- 15" away, the closest I could get it wasn't sufficient to 'stop' the housing. 6" away worked but it was then in the way of the carriage so I gave up.

Point being if a very powerful strobe, made for the job, can't do this close up what chance does a florry essence stand ceiling mounted and feet away ?

.

Ken_Shea
01-01-2010, 08:32 AM
The airplane maintenance shop I worked in had 8-foot fixtures mounted directly to the wooden trusses. When one of the ballasts failed, it got hot enough to ignite the wood, and that got our attention. We never smelled the stuff oozing out of the ballast and collecting in the fixture.

There was an airplane on jacks under the fire, so I climbed up into the overhead with a fire extinguisher to put out the small fire and disconnect the fixture.

Roger

Aircraft maintenance shops don't have 8' ceilings, that is probably why you didn't smell it as they have a unmistakable odor when they get hot and start melting down.

Lew Hartswick
01-01-2010, 09:56 AM
John, the phosphor decay is long enough that it VERY unlikely to
ever get a strobe effect to stop rotation visually.
...lew...

J Tiers
01-01-2010, 10:44 AM
John, the phosphor decay is long enough that it VERY unlikely to
ever get a strobe effect to stop rotation visually.
...lew...

Not entirely true....... But WAY true enough to count....

If you look closely, you will see that the moving item is blurred and obviously moving, but there is a green stop-motion image that does slow, stop, reverse etc depending on RPM and number of visible features.

ARC lights stop motion, fluorescents are arc lights with phosphors that decay slowly as mentioned, and are not the same thiing.

Strobing effect of fluorescents is an old wives tale.

Lew Hartswick
01-01-2010, 11:05 AM
Yea it depends on how much of the mercury emission lines and which
ones leak through the phosphor coating . The singly ionized line at
5460.74 would be the greenish one and I don't know if the arc
produces enough double ionized one at 6149.5 to make a visible
image of "orangish" or not.
...lew...

Paul Alciatore
01-01-2010, 12:21 PM
Well, just for fun I hung one temporairly overnight and let it run to see how hot it would get. It is warm by the ballast, but certainly not hot. So I suspect it will be fine in normal operation. I don't plan to leave them on unattended so that should be OK too. And there is the dry wall between them and any wood so I think it will be fairly safe.

On the strobe thing, this will depend on two things. First, the older ballasts operate at 60 Hertz so they will show a more apparent strobe effect as it is easier to see it at lower frequencies. Some of the modern ballasts use higher frequencies which make the strobe effect harder to see. It can still be there, but it is harder to see due to the second factor below.

The second thing is the persistance of the phosphors used in the tubes. They are excited by the radiation from the gas in the tube, which is very intermittant as well as invisible. When the phosphors recieve this radiation, they radiate visible light. But this radiation can be for a short or longer time depending on their persistence. If it is short enough, you will see the flicker, but if it is longer you will not because the next burst of radiation from the gas will come before it has a chance to die down. Different brands and types of tubes can/will show different amounts of flicker; if they show any at all.

CRTs used in TVs have relatively short persistence phosphors to better show the motion so the flicker is easy to see. Just wave your hand in front of a TV and see the individual fingers frozen in multiple positions. Other CRTs, like some used in scopes, have longer persistence to show very short events by keeping them on screen for longer times. This is all before modern displays of course. But persistance is a factor there also in spite of the fact that few manufacturers ever mention it.

To see a maximum flicker effect, as in the phonograph strobes, they use gas discharge lighting such as neon bulbs. I have one in a turntable that I still use. Photo flash tubes are even shorter persistence and can freeze even fast motion. I believe they can be as short as 10 micro seconds or perhaps even less.

It has always amused me to hear people who talk about how fluorescent bulb flicker irritates them, but they can sit and watch TV for hours on end and never complain. I work with one such person and he has read about the fluorescent flicker so it bothers him. He is a informercial script writer and has a TV in his office along with all incandescant lighting. I haven't the heart to tell him that the average CRT style TV is 1000% worse.

Your Old Dog
01-01-2010, 01:21 PM
As a former tv newsphotographer with a fire/police scanner in my car I won't be screwing any flourescent fixtures to my ceiling. Heard at least 1 - 2 calls a week due to defective ballast in a metro area of about 350,000. Almost as common as "meat on the stove" calls. I have the 4 footers and they are hung from the ceiling.

gellfex
01-01-2010, 01:31 PM
I see no distinction being made between electronic ballasts and the "bricks". I have a few of the former screwed directly to the bottom of joists. The electronic seem to just stop working rather than melt down, I think I've had only 1 melt. Unfortunately these are getting even shorter lived than they used to be. I'm lucky to get 2 years out of them now, but I still have a few 12 year old ones working fine.

lakeside53
01-01-2010, 01:46 PM
I have two shops... One with 14 20 year old "chain hung" 4 foot dual tube 40 watt T12 with reflector and old style magnetic ballasts... In the second (just finished) I mounted 12 4 foot dual tubes 32 watt T8 (electronic ballast) with NO reflectors directly to the ceiling. These T8 fixtures are rated for direct mount to a non-combustible surface. Both ceilings are painted white, and the wall a very light "off white". The new shop has dual light switching in two banks of 6. A lot of wiring...

NO COMPARISION....

With the tubes close to the ceiling, the ceiling is the reflector. The light is even, and almost no discernible shadows at working height.

The T12 hanging below the ceiling project little light to the ceiling so my lighting is a somewhat uneven.

The T8's start up instantly at low temperatures and provide excellent light. The T12's barely work in the winter...

My shops are generally unheated and stay about 41F in the winter. I leave the heat either ON or OFF for long periods, and I'm a cheapskate wrt electrial heat... so it's usually off. Turing it on from dead cold in this area makes for condensation on my iron...

I never realized how bad the lighting was in my old shop until I finished the new... Now I just need another $500 (and a bunch of time) to retrofit the old shop with direct mounted T8 fixtures. :(

Allan Waterfall
01-01-2010, 01:48 PM
The strobe timing discs on Tony Jeffries site work quite well under florescent light.
I originally set my VFD speeds using them.

Allan

J Tiers
01-01-2010, 02:29 PM
You can see the effect, but it is not nearly enough to fool anyone BUT a "fool" into thinking a moving object is not moving.

nheng
01-01-2010, 02:47 PM
I've mounted the Home Depot "Lithonia" brand 2 tube shop lights by letting them sit on cross braces placed on the face of the floor joists at 2 points each. Being flush has helped a lot with the appearance of the shop and eases the glare a bit too.

The Home Depot "Commercial" brand had 100% failure on all 3 units in a year. HD replaced them and I was told by several guys in their electrical department that the "Commercial" ones will ALL fail. Good to know. Additional ones will be Lithonia ... a lesser of two evils :(

Having electronic ballasts, these fixtures with the new, smaller OD tubes (I forget the number) will not give you a strobe effect and no humming either. From my own experience with emissions testing at work, they tend to operate at around 10kHz and above.

Den

Dawai
01-01-2010, 07:16 PM
There is a tiny bimetal thermal button that turns off the ballast when it gets too hot.. problem is.. it turns on and off till it wears out.. Sticks open, or sticks closed.

Yes. fire hazard exactly.. mount them away from anything that might ignite.. as long as the tiny electrical fire is contained in the metal fixture box.. no harm done to the building..

YEs.. Uncle JOhn.. they suck in cold weather.. flicker.. Even the screw in CF bulbs suck.. take a half hour to warm up..