# Watt ? Candle Power... ?

Discussion in 'Contact Printing' started by Ray Rogers, Mar 25, 2011.

1. ### Ray RogersMember

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Anyone know or can easily measure the c.p. of a "typical" 60W light bulb?

I have some old contact printing data for a paper that says that typically, an exposure of X seconds at a distance of 50 cm, to a 50 c.p. light source should be just about right.

So, what would this be in terms of todays (?) tungsten light bulbs?

What are typical c.p. values for 60 light bulbs of today?

I have found confusing and conflicting information,
but so far, the values I have come up with are:

60W=16 c.p.
or
60W=19.35 c.p.
or
60W= 64 - 72 cp

Anyone know if these figures are anywhere near correct?

I have some understanding of the many issues involved here, but as given, it was thought that the rating in c.p. as given at the time the paper was made, would be useful to people with differet lamps... I think it must have at least some "ballpark" accuracy,

so a crude approximation is fine....

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2. ### DWThomasSubscriber

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No doubt this can vary a lot, as by running a filament hotter, one can trade off lifetime for intensity. A quick Google search yielded an article that says 1 lumen = 1 foot-candle, and that to an approximation, dividing the lumens by 0.07958 will give an approximation of candlepower.

Some 60 watt soft white "long life" bulbs here claim 780 lumens with a 1500 hour life. That would work out to about 9800 candlepower.

I suspect there are some assumptions made that might be good to know about. But that exhausts my knowledge!

3. ### Photo EngineerSubscriber

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US 60 watt bulbs burn dimmer in Japan Ray, if you are on 50 CPS as is most of Japan.

PE

4. ### gmikolMember

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Not just 50Hz, but 100V nominal in Japan, compared to 120V in the US.

--Greg

5. ### Ray RogersMember

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The most likely guesstimate so far is that 50 candlepower equates to about 34.5W current tungstens...
So I am thinking just calling it 40W...

BTW
What watt lights are most people using for AZO and Lodi Ma?

6. ### tkamiyaMember

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Actually... half of Japan is on 60Hz and the other half is 50Hz. I really don't think frequency will affect brightness of incandescent light bulb... average power and RMS of sine wave AC is always the same regardless of frequency.

7. ### Photo EngineerSubscriber

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We saw a difference when I was there. They used 100V at 50HZ.

This made many things 5/6ths dimmer and you could see the fluctuations as a flicker.

PE

8. ### Worker 11811Member

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It isn't possible to generalize the wattage of any lamp to its light output. Every different manufacturer's product could be different and they often are. One way for manufacturers to compete is to say that their lamps are more efficient than some other brand. (e.g. "G.E. lamps produce more candle power per watt than Sylvania.")

It isn't possible to generalize the light output of any lamp in actual use based on its specs. Like others said, burning a lamp in one place (country) could produce different amounts of light due to different voltage, current and frequency.

It isn't really the brightness of a lamp in an enlarger that determines how photographic paper is exposed. It is the amount of light per unit of square measure. If you take a lamp of a certain brightness and shine its light through a lens so that its light is spread over a piece of 8x10 paper you will get a different exposure than if you spread that light onto a 4x5 piece of paper.
(For purpose of discussion, this assumes that ALL of the light goes onto the paper and nowhere else.)

1) Candle power is an archaic measurement that isn't used anymore.
2) Light intensity is usually measured in lumens but candle power and lumens don't measure the same thing.

Candle power measures the perceived brightness of a light source from a certain direction but lumens measure the total light output in all directions.

Take a candle of a certain size which is made of a certain kind of wax. Light it and make it burn at a certain rate then look at it from a certain distance. That is one candle power.

Take that same candle and put it inside an opaque sphere which is perfectly mirrored on the inside. Open a small portal in the sphere and use a photocell to measure the intensity of the light coming from that portal. You would be measuring how many lumens the candle produced.

You can not say that a lamp of a certain wattage will burn with a certain brightness and you can not directly compare candle power to lumens but you can say that there are APPROXIMATELY 12.57 lumens per candle power.

Your average 60 watt household light bulb produces 650 to 700 lumens when burned under standardized conditions.

650÷12.57=51.7

700÷12.57=55.6

Therefore you can estimate that a 60 watt household light bulb, burned under average household conditions might produce somewhere between 50 and 55 candle power, give or take...

If that don't do what you need, try a 50 watt or a 75 watt bulb.

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9. ### Ray RogersMember

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Thanks... So, rather than "convert", perhaps I should just try to get one measured. I wonder, is there anyplace on earth that can still make measurments in candle power?

Does anyone know of a "Light Museum" ?
Maybe Edison has a museum or something?

One thing I omitted, the specfic light was described as:

a "50 kerzigen metallfaden Lampe"
ca. 1910-1920's
Germanny

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10. ### Worker 11811Member

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"50 Kerzen Metallfadenlampe" is German for "50 candlepower metal filament lamp." (Literal translation.)

11. ### Steve SmithSubscriber

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The whole of the UK is on 50Hz and this is to fast to see as a flicker.

But we do have twice as much voltage as you!

Steve.

12. ### David A. GoldfarbModeratorStaff MemberModerator

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Here's a straightforward explanation of the various units of light measurement--

http://www.theledlight.com/lumens.html

Some light meters can give measurements in Lux or footcandles, including the "Light Meter" app for the iPhone, if you happen to have one.

13. ### Photo EngineerSubscriber

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Why not just make a test strip or so to get the right exposure?

PE

15. ### Kirk KeyesMember

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PE - I think Ray is trying to correlate historical infomation about materials with current ones.

16. ### Photo EngineerSubscriber

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I understand Kirk, but an exposure will allow him to do some back calculations or estimates at least. And the 50 hz power in Japan will throw everything off anyhow.

PE

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Shocking!

18. ### Photo EngineerSubscriber

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Steve;

When I was in Japan, I could see flicker! You are just used to it!

PE

19. ### Ray RogersMember

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Kirk is correct.

This material is simply no longer available.

Even if I had a sample, I am guessing the detailed exposure information provided at the time of it's manufacture would be more indicative of the fresh material than it's current speed would be.

As far as the 50/60 thing I don't really understand.. maybe when you were here the power was not quite up to specs or something... In anycase, there is none noticed in my area, but I am not looking for it- besides- I stay in 60Hz areas... I wish I could say the same thing about the flush toilet!

20. ### Photo EngineerSubscriber

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I think a 60hz flush toilet or a 50hz flush toilet would be a real pain in the butt!

I lived or visited both areas in Japan though and could see a difference in flicker and in brightness but that was long ago.

PE

21. ### hrstMember

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With incandescent bulbs, the flicker is so low that I would say it is impossible for human to see it. If you shoot a several frames in incandescent lighting with short shutter times (like 1/1000 s), they come up with almost exactly the same exposure. The filament has some heat capacity so it dims only very little in 10 milliseconds. And, the lower the lamp design voltage, the more heat capacity in filament. 12V halogens take literally a second to "shut down" completely!

However, with fluorescent lights, some people (but very few) actually can see some flicker, or not see but rather "sense" it. It is not usual, but some people report tendency to headaches in strong fluorescent light. Which part of the cause is the high level of "strong" light and which part is due to flicker, it's hard to say. I have attached a series of (digital ) pictures of a fluorescent light I shot at 1/1000s to show the flicker.

The frequency of the flicker is 100 Hz or 120 Hz because the light is generated on both half-cycles. As a comparison, the CRT television flicker is either 50 Hz or 60 Hz depending on the system, and film projection in the movies is 48 Hz or 72 Hz depending on the shutter type.

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22. ### Steve SmithSubscriber

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My company has made control panels and remote controls (hard to believe) for electric toilets for the Japanese market!

Steve.

23. ### bblhedMember

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You say that you can't see the flicker? I can tell you how you can see it.

This can get long winded and technical so I am going to try to keep it really simple. This works in the US, not sure about other places.
When Electricity is generated it is produced on 2 sides of the generator, both these "legs" of the power are delivered to your home by the power company and then when your home is wired the legs are used randomly throughout your home. If you sit in a room for a long time that is lit by only 1 incessant lamp doing something like reading then exit that room and go to another room that is again lit one single incessant lamp on the opposite power leg you will notice a slight flicker. You can also sometimes see this effect if you step outside on a dark night with no streetlights on.

Why? Your brain does a lot of really cool things and this is one of them, the light on one leg actually dims ever so slightly 60 times a second, you don't notice because it is slight, and happens quickly. Your brain notices but doesn't tell you and just adjusts to process visual information when it has the most light, this happens over time so you don't notice it. When you move to another space where the light is dimmest when the light in the space you were in is brightest you notice a slight flickering as your brain is trying to catch up and adjust. If you live all your life in 60Hz and are sudden thrust into 50Hz you will notice this as well because you have not developed the timing in tour brain for 50Hz, it will come eventually. If you live in a place where you see both 60 and 50Hz all the time you develop the timing for both.

Oh and if you made it through all that, why not just make some test strips?

24. ### lxdudeMember

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Hertz to think about it!

25. ### lxdudeMember

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So uh, where is the "user" in relation to the toilet that a remote control is needed?

26. ### Steve SmithSubscriber

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It sits on the wall and you pick it up when you need to use it.

Similar to this one: http://accidentalepicurean.com/wp-c...Wireless_toilet_control_panel_w._open_lid.jpg

I have often wondered about remote controls for car stereos too.... and why the remote controls for some hi-fi equipment includes a control to open and close the CD tray.

Steve.