Scaling Down Compact Flourescent Bulbs

Surface brightness. Due to limited phosphor lifetime, you can't make a fluorescent tube with anything like the surface brightness of a tungsten filament. The large diffuse radiating surface means that you can't get any sort of beam from such a bulb. Stick a couple of layers of Magic Invisible Tape on the bulb of an ordinary flashlight to get an idea of what this does.

LEDS are a much better bet.

Cheers,

Phil Hobbs

fluorescent

large

ordinary

...Although a HID flashlight does exist :

Right, arc lamps have much higher surface brightness than tungsten, even. Searchlights, for example.

That looks like a great flashlight, but I wouldn't want to try finding bulbs at Walmart.

Cheers,

Phil Hobbs

Three problems:

1. The voltage drop per centimeter of discharge length is low. Unless the discharge path is at least a few centimeters long, most of the voltage drop across the lamp will be electrode losses.
2. There is an optimum diameter for fluorescent lamps, and their efficiency decreases when you go below a couple centimeters and decreases a lot when you go below several millimeters in diameter.
3. When the "electron temperature" (average kinetic energy of free electrons, expressed in temperature terms) is best for producing mercury's shortwave ultraviolet wavelengths that make fluorescent lamps work (as opposed to other UV wavelengths, infrared, and infrared wavelengths from the argon also present, etc.) it is a limitation on how much UV the mercury can produce. You cannot exceed the same amount of UV in that spectral feature's bandwidth radiated by the same area of radiating surface of a blackbosy whose temperature matches the "electron temperature" in question. So you cannot get fluorescent lamps with the surface brightness of incandescents, LED chips, etc.

- Don Klipstein ( snipped-for-privacy@misty.com,

Short length and small diameter seem to be just one problem: a lot of volume is required for efficient flourescent lights.

There isn't any way to increase the surface area?

Why not use a really big reflector -- about

8 - 10 inches in diameter?

Bret Cahill

No, it really is a surface issue. There's no problem building _very_ bright mercury arcs, it's just that the phosphor toasts almost instantly if you go above a certain limiting flux level. This is why compact FLs are long twisted tubes and not spherical globes.

The area isn't the issue--it's the surface brightness in lumens/square cm/steradian.

Yes, of course, if you collect all the light from the bulb and image it on the wall, you can get a surface illuminance of 1/M**2 times the bulb's surface illuminance, where M is the magnification. Assuming you don't lose any, which is a fairly heroic assumption.

That isn't my idea of a flashlight, but don't take my word for it. Why don't you build it, and see how well it sells?

Cheers,

Phil Hobbs

In article , snipped-for-privacy@aol.com mentioned...

One problem is that they don't put out much light at temps near or below freezing. Fluorescents have been in use for exterior lighting for a long time here in So Calif, but then it doesn't get that cold.

Another problem is that the light output is spread out over a large area, so it's difficult to concentrate it into a beam. But I've got a Burgess portable fluo light that's from the '60s, and uses lantern batteries or an electric power cord. I couldn't afford to buy batteries for it, so I've always used it on the power cord. It has a short 15"(?) tube at the focal point of a chrome sheet for a reflector, to help direct the light to the front. But it's nowhere near as bright as a regular flashlight. Burgess - remember those batteries? :o)

If you want to know just about everything about lighting, check out Don Klipstein's web pages.

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fluorescent

large

ordinary

Much better bet for what?

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My email address is whitelisted. *All* email sent to it goes directly to the trash unless you add NOSPAM in the Subject: line with other stuff. alondra101 hotmail.com Don't be ripped off by the big book dealers. Go to the URL that will give you a choice and save you money(up to half). You'll be glad you did! Just when you thought you had all this figured out, the gov't changed it:

...

"Wats> Much better bet for what?

Light production for a given size.

In article , snipped-for-privacy@aol.com mentioned...

Well, where's the light going to go? Right back into its own surface and be dissipated as heat?

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The way a flourescent light works is very obvious once you strip off the phosphor layer inside the bulb. You then have what was very common in head shops and nightclubs years ago

--a black light.

The ultraviolet light produced by the mercury-vapor lamp is absorbed by the phosphors and re-radiated as visible light. The phosphors can only absorb so much energy without being destroyed. That's kinda like trying to cook a turkey at 650 degrees for 2 hours instead of 325 degrees for 4 hours.

. . .

Ooops. Spent too much time in heat and momentum transfer & forgot all about fields.

Pretty funny now that I think about it.

Use lenses or reflectors to get the light around the curved or pleated surfaces and away from the tube.

I don't immediately see what would preclude that or other tactics.

Bret Cahill

They're not any better efficiency than halogen bulbs, which are much _less_ efficient than fluorescent lights. See Don Klipstein's LED pages for more info on this.

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My email address is whitelisted. *All* email sent to it goes directly to the trash unless you add NOSPAM in the Subject: line with other stuff. alondra101 hotmail.com Don't be ripped off by the big book dealers. Go to the URL that will give you a choice and save you money(up to half). You'll be glad you did! Just when you thought you had all this figured out, the gov't changed it:

In article , jeffm snipped-for-privacy@email.com mentioned...

Ooh, charcoal! Now the trend is to deep fry the turkey outside in only an hour or so. Why didn't someone think of that low tech solution years ago? Or did it just go out of style for decades, then suddenly come back?

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In article , snipped-for-privacy@aol.com mentioned...

I was over at the Big Orange Box store the other day and thought about buying a couple screw-in fluo replacement bulbs for five bucke each, but decided against it, figuring that they were half the regular price because they were half as good and lasted half as long, or maybe less. These were three inverted U tubes, the other brands were the kind with the tube in a spiral or screw thread shape. I thought, what happens to all the light that is on the inside of inverted Us or the screw thread? I would guess that a lot of it doesn't make it out, but gets wasted as heat when it hits the other parts of the bulb. But it still beats an incandescent bulb!

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Don't be ripped off by the big book dealers.  Go to the URL
that will give you a choice and save you money(up to half).
http://www.everybookstore.com  You'll be glad you did!
Just when you thought you had all this figured out, the gov't
changed it: http://physics.nist.gov/cuu/Units/binary.html@@t@h@e@@a@f@f@l@u@e@n@t@@m@e@e@t@@t@h@e@@E@f@f@l@u@e@n@t@@

But aren't they more rugged and long-lasting?

. . .

In politics that's call "good reasoning."

They couldn't justify using that much grease?

Bret Cahill

Cost is a big factor, too. Perhaps the biggest factor. And LEDs are not cheap.

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FOR SALE: Nice parachute: never opened - used once.

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F o d d e r

f o r

s t u p i d " n o t

e n o u g h

i n c l d u d e d

t e x t " e r r o r

m s g .

Then it would not be compact anymore!