Beware LED lamps

Kilgallb · Oct 29, 2015

I replaced numerous light bulbs in my house with LED substitutes. That night I turned off the lights and could see it took over ten seconds for the LED lamps in my ceiling fixture to extinguish. I would bet there is a capacitor storing energy holding the LEDs on after the AC Power was removed.

I know cold cathode fluorescents glow for a while, but did not realize LEDs did too.

I removed the one in my dark room the next day. Back to incandescent lamps for now.

Mainecoonmaniac · Oct 29, 2015

I knew that fluorescent tubes glowed after shutting them off. That's why I don't use them in my darkroom. I know that LEDs are quick to start with no warmup but didn't know that they stayed on after turning them off. I have a UV led light box for alt processes. It seems to turn off instantly.

Truzi · Oct 29, 2015

Some LED "bulbs" have a coating or cover that fluoresces:
https://www.earthled.com/blogs/leds...-award-winning-bulb-10a19-lprize-pro-2700-900

Luis-F-S · Oct 29, 2015

I've used fluorescent tubes in my previous darkroom and strictly LED's in my present darkroom with no afterglow from either one. L

Steve Roberts · Oct 30, 2015

Without a capacitor, LEDs powered by the mains (alternating current) have a noticeable flicker running at 50Hz here in the UK (or 60Hz in the US). This can be annoying, can trigger epilepsy and can be downright dangerous if moving objects are viewed, owing to the aliasing effect (i.e. a rotating motor can appear stationary when it is in fact still moving). Hence the addition of a small capacitor to store energy and smooth out the variations in intensity as the LED follows the mains sine wave. With incandescent (filament) lamps this isn't a problem as the heat/cool cycle that produces light isn't quick enough to follow the mains frequency. Of course, with direct current such as in automotive applications, none of this is an issue.
Steve

RalphLambrecht · Oct 30, 2015

Kilgallb said:
I replaced numerous light bulbs in my house with LED substitutes. That night I turned off the lights and could see it took over ten seconds for the LED lamps in my ceiling fixture to extinguish. I would bet there is a capacitor storing energy holding the LEDs on after the AC Power was removed.

I know cold cathode fluorescents glow for a while, but did not realize LEDs did too.

I removed the one in my dark room the next day. Back to incandescent lamps for now.

It is amazing how hard it seems to be to beat the good old technology of incandescent light bulbs.new inventions are always better in some regard but always seem to have some shortcomings too.
I like their consistency;fast on and off and their price!

spijker · Oct 30, 2015

I have LED bulbs in my darkroom, both for the white main and the amber safelight. The white bulbs are Philips (800 lm, 3000 K) and they also take a few (3..4) seconds to go dark completely. So I just wait a few seconds before opening the paper or film. Not a big deal and certainly no reason to go back to incandescent bulbs. Consider it a minor inconvenience for a better environment. Plus, I like the whiter light that they give. But you may want to try some other brand bulbs. The big hardware stores are usually not fussy about returning a LEB bulb. I've done it in the search for a good replacement for halogen GU10 spots.

Fr. Mark · Oct 30, 2015

The tail off of light could be more of an issue in using LED's in enlargers. But maybe not if it is consistent.
Red LEDs are not 100% red, at least not samples I've had and can fog film (red blind Ortho film) and printing paper if too close/intense.

Ive noticed a long glow coming from t8 fluorescent tubes whole tray developing pan films but it is dim enough it has not fogged films. They do not fade to completely dark even in 10+ min Dev. Times.

AgX · Oct 30, 2015

I encountered even incandescent (halogen) lamps that showed fluorescence.
The manufacturer Philips preferred not answer my inquiry on this.

bdial · Oct 30, 2015

I am using LED bulbs in several places around my house, though none in the darkroom for white light so far.
Most of them go out as quickly as incandescents, but I do have a couple that do a fade-out for a half second or so.
As mentioned, it's easy enough to just pause for a second or two if you have slow acting bulbs. I rarely have anything light sensitive out more than several seconds after lights out anyway, but it's good to be aware of possible hazards like this.

Steve Roberts · Oct 30, 2015

I notice an effect with the incandescent lamp in my enlarger. When switching on the enlarger, the light it emits is briefly brighter than expected before stabilising. We're probably only talking about a quarter of a second. I've always taken this to be because at the point of switch on the filament is cold, its resistance at its lowest, hence higher current flow and more light. However, once that current is flowing the filament heats up rapidly, its resistance increases, current falls and light output falls correspondingly as it reaches a state of equilibrium.
Steve

M Carter · Oct 30, 2015

I've noticed the spiral flows in my darkroom have a bit of a ghost-glow when shut off - it's hard to verify that due to persistence of vision or retina-burn-in or whatever that effect is. You have to close your eyes, switch off the light, and then open them quickly to verify it.

In my case, it's very dim and fades in a couple seconds - I doubt I could get from the light switch to the paper drawer that quickly!

I do want to put in some halogen track lights on a separate switch to view prints though.

bobwysiwyg · Oct 30, 2015

We have replaced virtually all our non-photographic related lights with LED's. The performance and pricing has improved dramatically and it has had a favorable affect on our electric bill. I have noticed a "very" brief delay in turning them on, have not noticed the referred to slow extinguishing of all light, but really never paid attention. I will tonight... if I remember.

David Brown · Oct 30, 2015

Apparently some fluorescents fluoresce after being turned off. Anecdotal evidence suggests some for minutes, some for seconds, some not at all.

I’ve had leds over my sinks for print vieing for a couple of years now. Never noticed a glow. However, I recently changed out the 300 watts of incandescent general lighting in my darkroom for leds. They do seem to take about a second or so to fully turn off. Is that the same thing as fluorescing, as with the flourescents?

“Red leds are not safe.” Well, I preached this for years until I ordered the ones that several people swore by, to do a proper threshold test and prove that I was right. I was wrong. They tested good with Ilford MGIV for 10+ minutes! (I didn’t bother to test for a longer period – the Kodak test is for 7 minutes)

So, some may glow, some may not. Good to know that, but let’s not overgeneralize or jump to conclusions. Just test your safelights and look at the room lights when they go off.

Your-mileage-may-vary …

mgb74 · Oct 30, 2015

RalphLambrecht said:
It is amazing how hard it seems to be to beat the good old technology of incandescent light bulbs.new inventions are always better in some regard but always seem to have some shortcomings too.
I like their consistency;fast on and off and their price!

The have their benefits, primarily their low initial cost. But have you ever wondered how much electricity you're using to power air conditioning (especially in central Florida) just to overcome the heat you've generated with an incandescent bulb?

M Carter · Oct 30, 2015

David Brown said:
Red leds are not safe. Well, I preached this for years until I ordered the ones that several people swore by, to do a proper threshold test and prove that I was right. I was wrong. They tested good with Ilford MGIV for 10+ minutes! (I didnt bother to test for a longer period the Kodak test is for 7 minutes)

Indeed, those little round bulbs that were enthused about here? Those are my hell yeah, "product of the year" find. It's like daytime in my darkroom now. And they're damn cheap, too.

I've been brush-coating canvas with Foma liquid emulsion - like, 20x24 pieces. It's a lifesaver to be able to angle a bright safelight next to the canvas to check the brushstrokes and watch for loose hairs and junk. And it's killer for lith printing. Can't recall who did all the research and dug up the spectral tests for those babies, but he has my eternal thanks and the debt of a nice cocktail if he's ever in my town.

Do I sound happy?

fotod69 · Nov 28, 2015

spijker said:
I have LED bulbs in my darkroom, both for the white main and the amber safelight. The white bulbs are Philips (800 lm, 3000 K) and they also take a few (3..4) seconds to go dark completely. So I just wait a few seconds before opening the paper or film. Not a big deal and certainly no reason to go back to incandescent bulbs. Consider it a minor inconvenience for a better environment. Plus, I like the whiter light that they give. But you may want to try some other brand bulbs. The big hardware stores are usually not fussy about returning a LEB bulb. I've done it in the search for a good replacement for halogen GU10 spots.

I've building a new darkroom and used 4 foot daylight balanced tubes for over 25 years without a fluorescent afterglow. I bought some new 5000K 4 foot tube fixtures using the smaller Phillips 800 series 32 watt tubes and they appear to have and afterglow that lasts a few minutes. Does anyone know of a daylight balanced tube of the new smaller diameter that doesn't have this problem?

Thanks, Dennis

AgX · Nov 28, 2015

I am surprised. To my understanding all fluorescant tubes show an afterglow.
But I would not be surprised if the duration is different depending on pigments, determining light temperature but also colour rendition.
Which means there are two factors to look for when choosing a tube for its light quality.

The easiest way to control afterglow is to use flaps on the luminaire.

john_s · Nov 28, 2015

Steve Roberts said:
I notice an effect with the incandescent lamp in my enlarger. When switching on the enlarger, the light it emits is briefly brighter than expected before stabilising. We're probably only talking about a quarter of a second. I've always taken this to be because at the point of switch on the filament is cold, its resistance at its lowest, hence higher current flow and more light. However, once that current is flowing the filament heats up rapidly, its resistance increases, current falls and light output falls correspondingly as it reaches a state of equilibrium.
Steve

This has always made sense to me. For that reason, I have favored domestic light dimmers that provide a soft start which avoids the initial surge (most relevantly when turned on to the brightest setting, of course). The frequent blowing of an incandescent globe the moment it's turned on is also explained by this: being the high initial current.

However, I did read somewhere (can't remember where) that the effect is so brief that it doesn't actually exist. I suppose measurements would have to be taken to ascertain the actuality.

480sparky · Nov 28, 2015

Steve Roberts said:
I notice an effect with the incandescent lamp in my enlarger. When switching on the enlarger, the light it emits is briefly brighter than expected before stabilising. We're probably only talking about a quarter of a second. I've always taken this to be because at the point of switch on the filament is cold, its resistance at its lowest, hence higher current flow and more light. However, once that current is flowing the filament heats up rapidly, its resistance increases, current falls and light output falls correspondingly as it reaches a state of equilibrium.
Steve

That is precisely what happens. When cold, the filament is literally a dead short. But the quick temperature rise prevents the operation of the average fuse / breaker. As the temperature rises, the resistance increases tremendously, and eventually it will reach a point where it and current flow will even out and stay at a steady rate.

RalphLambrecht · Nov 29, 2015

bobwysiwyg said:
We have replaced virtually all our non-photographic related lights with LED's. The performance and pricing has improved dramatically and it has had a favorable affect on our electric bill. I have noticed a "very" brief delay in turning them on, have not noticed the referred to slow extinguishing of all light, but really never paid attention. I will tonight... if I remember.

I noticed the biggest impact on my electric bill after installing solar panels on my roof.My bill dropped by 90%.I'm back to incandescent and only good(fast and stable white)CFLs.

Beware LED lamps

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