Petzl Zoom Bulb

[ianball11]

I'm trying to match a Petzl Zoom bulb so I can buy a few, but the only identification marks on it are the Petzl name and 4.5V.

Any idea what ampage the bulb that comes with a zoom is?  It's the tubular and nippled bulb not a spherical bulb.

I bought a few from Caving Suppies in Buxton to test them out but none of them seem as bright.  I bought 4.0V 0.5A, 0.85A and a 1A bulb to see if the extra rating would ioncrease the brightness significantly enough to do with the loss of duration but I can't see a huge power difference.  Does the 4.0V as opposed to 4.5V rating make a difference?

I'm assuming from struggling through the principles of Ohms law that it might as I imagine the resistance of the different bulbs is similar? Or am I barking up the wrong tree. 

Many thanks,

Ian B.

 

[workshopmonkey]

The 4v bulb will blow in a zoom power set up of 3aa batts giving 4.5v. Using good old ohms law u can calculate the res ie amps/volts = res. Electrical superstotres like Marconi etc will sell you bulbs by the bucket load or check online for retailers. 

 

[ianball11]

That doesn't sound good, it's got the 4.5V LR12 battery cell.
Back to the drawing board.
Ian B.

 

[workshopmonkey]

the bulb with the nipple on top is a halogen, are the ones you bought standard bulbs, this would account for the lack of power. Petzl still do the halogen replacement for the zoom at about 4 quid depending where you get it. This will only say the volt rating and amps on it.

 

[ianball11]

The replacement ones I bought are the same shape as the Petzl one but they are no brighter even with a larger ampage rating.  I think I should have a test in a dark place, maybe the ligt is more dispersed or something like that.

Having said that they will probably blow up anyway rating at 4V.

Thanks for replying, very kind.
Ian B.

 

[francis]

Could This be an alternative? I use the same one, just for 4 cells in my Duo and love it

Francis

 

[Agrophobic]

Hi.
if you look inside the cover of your zoom battery holder, current ratings and voltages are listed, if yours han't got it, mine says Standard bulb 3.8v 0.22A, Halogen 4v 0.5A.
HOWEVER- i've had 4v bulbs blow in my zoom so now use standard 4.5v petzl bulbs which draw about 0.25A as measured with a meter. available from brewsters ltd.
I'm tempted by the led replacement bulb but at £15 delivered it seems a bit steep, has anyone tried em?
Ps- sorry to piss on your carbide workshopmonkey, but try volts/amps=resistance.
not thet resistance matters, its power you want which is voltsXamps=watts.

 

[workshopmonkey]

No worries Aggy old boy carbide dry as tinder

 

[CaverA]

I bought some Krypton or Crypton bulbs from a hardware shop in Lymouth, after my Zooms bulb blow while camping. If thats helpful!

Sam

 

[potholer]

For a given bulb, there's a trade-off between life and brightness/efficiency.
Under-driving the bulb will usually result in rather longer life, but the bulb runs cooler, which means it is less efficient and dimmer. Overrunning a bulb will shorten its life, but give brighter light.

The battery voltage will droop under load, and droop further the greater the current drawn.
This effect is more pronounced as the battery discharges, and more noticeable on alkalines compared to rechargeables.
Higher current bulbs will cause the battery voltage to drop more, which can end up with the bulb being under-run simply because the battery isn't capable of supplying the oomph.

I just tried attaching an old Oldham bulb to a fairly new 4.5V flatpack alkaline. Off that battery, the bulb draws about 0.9A, and that draw is sufficient to reduce the battery voltage to pretty exactly 4.0V, so a 4V rated highish current bulb in a zoom might well not be at all overdriven.

In practice, even if run off a perfect voltage source which didn't droop under load, I wouldn't expect bulbs of the same rated voltage, and with rated currents of 0.85 and 1A to be easily distinguishable from each other. The human eye doesn't respond to lighting in anything like a linear manner.
The difference between a 0.5A and 1A bulb should be noticeable in the right conditions (using them side-by-side to alternately illuminate stuff), but it might be harder to see a great difference if you were swapping them into the same torch one after another with any kind of time lag. Even where you see a difference, it may not look like a 2x difference, especially with any delay between looking at the lighting from the 2 bulbs.

Confounding factors:
For different-current bulbs of the same rated voltage, the voltage droop effect will tend to equalise performances a little - the voltage will droop less with a lower-current bulb, so it will be run slightly harder.
On the other hand, low-power (ie torch-size) halogen bulbs tend to be such that the lower the power, the lower the efficiency, which can tend to increase the gaps in output between bulbs of different power compared to what might be guessed from the raw voltage/current figures.
Those two confounding factors will tend to cancel out to at least some extent, since they pull in different directions.

 

[ianball11]

Excellant post.  I've read it afew times and have to concede that I don't fully understand it all, or more likely I understand there is more to it than ehat I first thought.

Thinking about it 0.85 and 1 isn't quite the 0.25, 0.5, 0.75 and 1 increment that I was trying for.  And also swopping bulbs out of the same torch was never goig to be a decent test, I wanted to use the same reflector to see if the slightly scuffed plastic caused a diffusing effect. 

Thanks everyone.

Ian B.

 

[potholer]

There are a lot of complications relating to exactly what the light output is of a given bulb depending just how hard it's driven, which in turn depends on the battery, etc, but the main point is that a 15-20% difference in light is likely to not look great, if it's noticeable at all.

Just think of regular domestic light bulbs. If you had a 5-bulb fixture in the ceiling with the bulbs all lighting the same area, and one bulb blew while you popped into the next room, or even while you closed your eyes for a few seconds, would you usually notice the change?

 

[Agrophobic]

Just to make this even more technical- doubling the current ie-0.5A to 1.0A dosn't double the brightness. due to inefficiencies and heat. allthough going from 0.25 amp to 0.5 amp will be more noticable than going from 1 amp to 2 amp.

 

[Downer]

I dug out my old zoom, fitted a new lead, which had corroded away and then did some battery tests only last week, using old-fashioned (standard) "flatpack" alkaline batteries and 4V bulbs.

The normal (Petzl) 0.5A bulb ran the battery flat in 6.25 hrs
A 0.85A bulb (Speleo) flattened it in 3 hrs

The cut-off was pretty sharp though there was in both cases a slow dimming throughout the run-down. There was negligible difference in the brightness.

The reason for the lack of performance on the bigger bulb became clear when I measure the voltaged on the battery terminals. After about half an hour, the battery was managing a respectable 3.9V on the smaller bulb but only 3.5V on the larger one due to the heavier load. 10% voltage drop makes a big difference with a halogen bulb.

The battery characteristics also account for why a bulb that is less than twice the size of the standard one, runs the battery flat in under half the time. The battery is simply less efficient all round when heavily loaded.

And there's another disadvantage in using a bigger bulb. I like to pack the thread of the zoom with vaseline to keep water out - the bigger bulb runs significantly hotter and the grease dribbles out. I suppose I could research different greases but enough is enough! Also, the bulb is slightly different shape, making the focussing point for an optimum spot a bit too close to the off position. All in all, I'd advise sticking to the standard bulb. However, a conversion to modern NiMH batteries would probably make the dimming imperceptible and might squeeze a bit more light out of the bigger bulb as their performance is excellent. unfortunately, though 2700mAH into a 850mA lamp will only give you about 3hrs of running so you may need to take a spare set.

Hope that's useful data.

 

[ianball11]

It's spot on, no mediocre pun intended.

By upping the ampage of the bulb I would get a much lesser burn time for negligible extra output, so pointless!

Isn't the petzl bulb a 4.5V bulb and would that make a difference?

Ian B.

 

[Downer]

"Isn't the petzl bulb a 4.5V bulb and would that make a difference?"

You had me worried then, but I've just checked and they are both 4V!

Certainly, running a 4.5V bulb on 4V will half its light output while the current through the bulb only drops a little bit - not the 11% that Ohms Law suggests, because the resistance of the bulb will be less at the lower temperature.

 

[Downer]

p.s. 4.5V on a 4V bulb shouldn't blow it immediately, but it will reduce the life to just a few hours and greatly increase the chances of the bulb failing at switch-on. The usual conversion kits go to just 3 AA cells which means a pretty steady 3.75V for most of the battery life if you use decent rechargables. Unfortunately, there is a brief run-in period when the battery voltage is higher, up to 4.5V in fact, bad news for 4V bulbs and disastrous for anything lower. You could bleed off the first 5- 10% of their charge, of course, using, say, a 6V bulb, but the chances are you'll forget sooner or later and realize twenty minutes into a trip that you've just used up 3/4 of your bulb's life with your lovely bright white beam. I know I would.

Is there a thread about building a regulator for filament lamps? I can make some suggestions for anyone who wants to do it.

 

[potholer]

I'd guess that most people who'd be likely to go to the trouble of building electronics into a light these days would just slap an LED in as well, rather than sticking with halogens.

 

[Downer]

Personally, I detest the sepulchral blue beams of LED lamps so I shall stick with halogen!

 

[potholer]

There are softer-white (yellower) LEDs available, though personally, I prefer a more mainstream white.
Halogens certainly do a better colour rendition job on surface vegetation, but to me, a good white LED does a more realistic job of lighting things up underground than a caving-size halogen. Going underground from daylight, there's no great colour shift, whereas a halogen is definitely yellow, and the deficiencies in the LED spectrum don't seem to be anywhere important.

Compared to 2 or 3 years ago, when efficiencies were roughly comparable, the efficiency differences these days means that LEDs stomp all over halogens, especially for homebuilds using the bleeding-edge stuff rather than older devices filtering through a long supply chain.

Small halogen bulbs give something under 20 lumens/watt, the best LEDs now coming on stream are hitting 100lm/W, and still climbing. That much difference can override all but the strongest preferences for a halogen's spectrum.