Safelight Filter Voltage and Wattage

[BobUK]

I am sorting out my small collection of Film, Paper and Chemical instruction sheets that came with the various products I have used in the past.
Currently looking at the instruction sheet for KODALITH Ortho Film 2556. Way past its use by date, but I still have a roll, and will see if it is still functioning.

When it comes to the safelight instructions for the film I was interested to read about recommended wattages for bulbs.


"Safelighting: With care, a safelamp fitted with a KODAK Safelight Filter, No.1A (Light Red) and a 200-250 volt pearl lamp up to 25 watts may be used at a distance of 1.2 metres from the film.
For countries and areas having 110-120 volt supplies, a 15 watt pearl lamp is recommended."


This is the first time that I have seen a leaflet recommending different wattage bulbs recommended for different voltage supplies.
It's obvious really thinking about the equation Power = Amps x Volts

Looking at the KODAK Data Sheets T10845 07-99, the one detailing the various safelight filters including transmission graphs, there is no mention of voltage supplies and wattages.

Also, the leaflet supplied with KODAK Filter Glasses, "How to select and use KODAK SAFELIGHT FILTERS." 30819-285 apart from mentioning 25 watt bulbs makes no mention of different voltage supplies.
This may be because the leaflet is printed in England, and 240v is expected. PL1064 (599)

The lesson that I have learned is, when safelight illumination recommendations are given by people on the internet, it needs to be born in mind their location and my location.


Iv'e learned something today

 

[koraks]

Odd. 15W = 15W of heat, regardless of voltage. Maybe it had something to do with commonly available bulbs?

 

[DWThomas]

Haven't spent enough time across the pond to buy any light bulbs, but I suspect Koraks is correct. Here in the US the bulk of standard household bulbs were 25, 40, 60, and 100 watts, but there were also 7.5 and 15 watts available "back in the day." I use 15 watts in my Kodak "bullet" safelights but may have to improvise for the next replacements as a quick look in the big box store sites doesn't show them, at least in the E-26 base. (Fortunately, the 15 watters run way longer than brighter ones.

 

[ic-racer]

One might also consider heat dissipation of the lamp in the sealed [Kodak] lamp housing when choosing a lamp.

 

[BobUK]

I am not an electrician, but have puzzled out an interesting connection between the two bulbs and voltages.

Power / Voltage = Current.

Using average voltages we get

25w / 225v = 0.111 amps.

15w / 115v = 0.130 amps.

So both bulbs draw nearly the same current.

The current in amps has to be the thing that controls the bulb brightness.



I think this is what people call "a light bulb occasion."

 

[Ian Grant]

There may be a slight difference in colour temperature and brightness, a 110-120v tungsten bulb needs twice the amps compared to the equivalent 200-240v, despite using the same energy,

I've just had this discussion with an electrical engineer who confirm this.

Ian

 

[koraks]

The current in amps has to be the thing that controls the bulb brightness.

Power controls brightness. Efficiency of a bulb like this will be similar, in the single digit percentages.

There may be a slight difference in colour temperature and brightness, a 110-120v tungsten bulb needs twice the amps compared to the equivalent 200-240v, despite using the same energy,

There can always be differences in bulbs, but they're not inherently tied to current or voltage. Without knowing the impedance and physical size of the filament, you can't say.

 

[BobUK]

There may be a slight difference in colour temperature and brightness, a 110-120v tungsten bulb needs twice the amps compared to the equivalent 200-240v, despite using the same energy,

I've just had this discussion with an electrical engineer who confirm this.

Ian

In my examples I used a 15 watt and 25 watt bulb.


Using a 25 watt bulb on both 225 volts and 115 volts in the equation POWER / VOLTAGE = CURRENT (in amps)

it does give 0.111 amps and 0.217 amps. Double the current.



So I will agree with your electrician.

 

[koraks]

I think I'll agree with physics.

 

[BobUK]

Power controls brightness. Efficiency of a bulb like this will be similar, in the single digit percentages.



There can always be differences in bulbs, but they're not inherently tied to current or voltage. Without knowing the impedance and physical size of the filament, you can't say.

The wattage of the bulb is tied in with the current and resistance of the element with the equation.

POWER = (AMPS X AMPS) X OHMS ( no idea how to type indices on this keyboard hence the long winded typing.)

Power = Current squared x Resistance

 

[koraks]

Color temperature correlates with physical temperature of the filament (among a few other things). Now go ahead and list the factors that determine filament temperature. You've identified part of it, but not all. Once you've gone through the list, you'll notice that you can't say "a higher current will result in a higher/lower color temperature". It's insufficient information to make that claim.

 

[titrisol]

Is this why enlarger bulbs are 150-200W in Europe but 75-100W in USA?

 

[koraks]

Is this why enlarger bulbs are 150-200W in Europe but 75-100W in USA?

No, because they're not. We also have 75 and 100W bulbs.

If you plug in a 100W 115V rated enlarger bulb into a 230V socket, you don't magically get a 200W bulb. You get a bright flash, darkness and a bulb that's black on the inside.

 

[titrisol]

No, because they're not. We also have 75 and 100W bulbs.

If you plug in a 100W 115V rated enlarger bulb into a 230V socket, you don't magically get a 200W bulb. You get a bright flash, darkness and a bulb that's black on the inside.

IIRC The Ph211 (75W) in US was replaced by a Photocrescenta (150W) when I moved to NL

 

[Ian Grant]

There can always be differences in bulbs, but they're not inherently tied to current or voltage. Without knowing the impedance and physical size of the filament, you can't say.

That does not explain Kodak's recommendation:

"Safelighting: With care, a safelamp fitted with a KODAK Safelight Filter, No.1A (Light Red) and a 200-250 volt pearl lamp up to 25 watts may be used at a distance of 1.2 metres from the film.
For countries and areas having 110-120 volt supplies, a 15 watt pearl lamp is recommended."


The relationship between Power (Amps), Volts, Resistance, is not linear when it comes to Light output. The electrical engineer I was talking to last night quoted a formula, and that indicated that the same wattage a120v lamp would be slightly brighter than a 240v lamp.

No, because they're not. We also have 75 and 100W bulbs.

If you plug in a 100W 115V rated enlarger bulb into a 230V socket, you don't magically get a 200W bulb. You get a bright flash, darkness and a bulb that's black on the inside.

While used at 220-240v the 100w modelling lamps for my old Elinchrom,22 flash give out far more light than a normal 100w tungsten bulb, technically they are 100w 180v overvolt bulbs according to my June 1980 datasheet, and spare bulbs, with a 60 hour rating. The same principle is used for Photofloods.

Ian

 

[BobUK]

Color temperature correlates with physical temperature of the filament (among a few other things). Now go ahead and list the factors that determine filament temperature. You've identified part of it, but not all. Once you've gone through the list, you'll notice that you can't say "a higher current will result in a higher/lower color temperature". It's insufficient information to make that claim.

Hello again Koraks
In my second post I mentioned "bulb brightness", "not colour temperature."
You are going a bit fast for me. I have to learn to walk before I can run.
I need to do a bit more Googling yet to find out what controls colour temperature.

Thanks.

 

[koraks]

In my second post I mentioned "bulb brightness", "not colour temperature."

OK, sorry - your argument and Ian's got sort of mixed up. But the same things I said still apply. Brightness is a function of physical size + power dissipation, among others. There's no direct relationship between current and brightness as such. It goes through power, plus it has to do with a host of other variables.

Think about it - if only current had mattered, lighting systems would have been more efficient at very low voltages (thus high currents). If that were the case, your wall outlet wouldn't give 115V, but 1.15V or so, so that your 100W bulb wouldn't have drawn close 1A but close to 100A instead. After all, if your reasoning, it would have been far brighter that way! But it doesn't work that way.

 

[reddesert]

Bulbs made for 110 V and 220 V are different, if you take say a 60w bulb for each, the bulb for 220V will have a larger resistance, roughly four times larger. It probably has roughly the same amount of tungsten, just arranged in a longer thinner filament. Power = V^2 / R = V * I, so this keeps the power the same between the two bulbs.

This is approximate since bulbs are non-Ohmic, meaning their V-I curve is not linear. And their light output is not linear with voltage; if you undervolt a bulb it's very dim and redder. The non-Ohmicity and efficiency are probably what Ian's EE friend is referring to.

Wattage should be a good predictor of light output, although it's not perfect: you can buy 60w bulbs with different amounts of lumens. It's not obvious why Kodak recommended different wattages at 110 vs 220, but maybe these specific bulbs in this size differ. The current of ~ 0.1 amps is fairly low so I don't think it was a limitation of the components like the socket, switch, or wiring.