Light Bulbs

[wrigley]

I go into Home Depot last night to get some light bulbs for the house. I need 25W and 40W bulbs. I paid $2.97 for a 2 pack of GE soft white 25W bulbs, and $.88 for a 4 pack of GE soft white 40W bulbs. Same manufacturer....what gives with the price? Neither of them were on sale!

Mike

 

[OAG]

Everyone must be buying CFL's so the incandescent ones are way overstocked?

 

[W2R]

I go into Home Depot last night to get some light bulbs for the house. I need 25W and 40W bulbs. I paid $2.97 for a 2 pack of GE soft white 25W bulbs, and $.88 for a 4 pack of GE soft white 40W bulbs. Same manufacturer....what gives with the price? Neither of them were on sale!

Mike

I don't know! Maybe GE sells more 40W bulbs (than 25W bulbs), bringing the price down? Doesn't sound like a likely explanation but I can't think of any other.

 

[JPatrick]

Bulb prices are all over the place..I use GE Reveal ( costly, but worth it IMO) and I find Wal*Mart generally whips all the others by 20 - 30%.
In this particular line, the Depot seems to always be the highest..

 

[TromboneAl]

I paid $1 for four globe-enclosed CFLs the other day. Twenty-five cents each.

 

[SteveL]

For those who like the quality of the old style of lights for some uses, like reading, you might try getting 130Volt bulbs. Their lifespan can be amazing (although of course they use more juice). We have some flood lights in our hall ceiling and outside decks that were installed by the contractor in 1979. Hard to believe.

 

[omni550]

For those who like the quality of the old style of lights for some uses, like reading, you might try getting 130Volt bulbs.

Where, typically, would I find these for sale?

omni

 

[SteveL]

Both Home Depot and Lowe's sell them, usually they are call contractors/commercial. You have to ask the store.

I got into this voltage thing, because when we moved into this house, when we put in bulbs in lamps, they lasted 6 weeks or so. Came to find out that our utility runs the voltage at the high end usually around 123V. Bulbs that are rated for 115v, don't hold up against this situation.

 

[calmloki]

W/ regard to 130V bulbs, we used them in a number of applications but no longer do. They create much more heat - if used with the base up and the glass envelope down we found that the base of the bulb would discolor to a grey as would the receptacle. The insulating sleeve around the receptacle would get so hot it would crumble and we ended up replacing light fixtures. If you look at the lumens put out by the 130V bulbs you find they are much lower than comparable wattage 120V bulbs. (think that a 75W 130V bulb put out less light than a 60W 120V as i recall). They do last much longer though.

 

[SteveL]

The rated lumens of a bulb are correct only if the real voltage is the same as the rated voltage of that bulb. In our situation with voltage 7% higher than the 115 bulb rating, bulbs burned hotter, and brighter, and burned out sooner. The 130v bulbs have tougher filaments, and would produce about 95% of the stated lumens. (130v divided by 123v).

We haven't had the problems mentioned by calmloki, but that doesn't mean that you couldn't.

 

[JOHNNIE36]

I paid $1 for four globe-enclosed CFLs the other day. Twenty-five cents each.

Al, where did you find CFL's for 25c each? Two years age when we moved into our new house I change every bulb out to CFL's after a couple months. There's quits an energy savings and the CFL's last much longer. Haven't had one burn out yet. They have all kinds out now--spot light type, flood type and various wattages. I'm still unsure about what happens if you break one. Mercury, you know. Have heard a couple horror stories but don't know how true they are. I've been sold on cost effectiveness since 1992 when I was president of a condo association. We went out on a limb and changed the entire lot of bulbs for CFL's. The energy savings was outstanding and we didn't have to go around changing burned out incandescents. More on CFL's--I find that some brands take about 30 seconds to come to full lighting capacity--mostly the flood type. I never use anything less that 13 watts which is equivalent to a 60w encandescent. Anyone out there have experience tieh the CFL's (good and/or bad)?

 

[calmloki]

Was just looking for some simple math - found this in Wiki:
Incandescent light bulb - Wikipedia, the free encyclopedia
(look at voltage, lifetime, light output section)


and this from Sylvania (see page 10):
View Engineering Bulletin

In that paper it's noted that a 60W 120V bulb operated at 125V will have increased luminosity from 890 to 1032 lumens - it's lifetime, however will only be 56% of it's 120V rated life! If Steve has higher than normal line voltage it would have an extreme effect on his bulb lifetime - much greater than i expected.

(oh - I want simpler math)

 

[samclem]

The last time I went to Europe I brought back a few 100w 230V incandescent bulbs. They burn very dim at 120V (looks like the equivalent of a "regular" 120V bulb of about 20 watts) and the glass doesn't even get too hot to touch. I bought them to use in small "spot heat" applications (e.g. a drop-light placed inches from the well pump switch in the garage on cold nights, etc). I wanted a very high reliability heating element, and I expect this bulb will probably last 15 years even if I left it on continuously.

Calmoki: I'm surprised the 130V bulbs would cause excess heating of the fixture compared to 120V bulbs. Any theories on this?

 

[TromboneAl]

Al, where did you find CFL's for 25c each?

Those were at a RiteAid drug store. The brand is Greenlite. They also had some GE brand spirals for 33 cents each. Price may be low due to PG&E subsidies.

It's very common to see CFLs for under a dollar around here. I find that these cheap ones are lower quality, in that some will burn out after only a month or so. I got a bunch at Costco for a 15 cents per "bulb," but about 6/10 of those failed almost immediately. The remaining 4 are still going fine.

These globe type ones are nice, since they exactly match the existing incandescent bulbs (which are unscrewed so that they are off):

Most (all?) of the CFLs produced today come on immediately, although they take a minute or two to come to full brightness.

The worry about breakage is way overblown, partly due to an urban myth story of someone who broke one and paid thousands for a hazmat team to clean it up.

Now that prices are so low, CFLs are appropriate even for lights that are on for short periods.
​

 

[FIREd]

Most bulbs we have around the house are CFLs (overheads, spots, table/floor lamps, etc...). I used to hate the light CFLs produced at the beginning (you know, the harsh white glow typical of fluorescent lighting). I like the warm glow of incandescent bulbs. But now that they have come up with CFLs producing warmer light, I don't mind using them. In area where I want extra warmth, I use them in lamps fitted with shades that are lined with a golden reflective paper on the inside.

 

[calmloki]

The last time I went to Europe I brought back a few 100w 230V incandescent bulbs. They burn very dim at 120V (looks like the equivalent of a "regular" 120V bulb of about 20 watts) and the glass doesn't even get too hot to touch. I bought them to use in small "spot heat" applications (e.g. a drop-light placed inches from the well pump switch in the garage on cold nights, etc). I wanted a very high reliability heating element, and I expect this bulb will probably last 15 years even if I left it on continuously.

Calmoki: I'm surprised the 130V bulbs would cause excess heating of the fixture compared to 120V bulbs. Any theories on this?

I'm guessing, and will gladly defer to a lighting engineer. But. Wiki says this:
Approximately 90% of the power consumed by an incandescent light bulb is emitted as heat, rather than as visible light.[47]
Luminous efficacy is a ratio of the visible light energy emitted ( the luminous flux) to the total power input to the lamp. It is measured in lumens per watt (lm/W). The maximum efficacy possible is 683 lm/W for monochromatic green light at 555 nanometres wavelength, the peak sensitivity of the human eye". And"...This comes about because the lower voltage lamps have a correspondingly thicker filament which has a smaller surface area than its thinner higher-voltage counterpart. The smaller surface area reduces the rate at which the filament evaporates which allows the filament to be run hotter for the same life". I am of the opinion that this is backwards, and that a thicker filament with less surface area will be associated with the higher voltage bulbs. Seems to me that a greater surface area/volume would result in higher heat at a given voltage and with the higher heat more of it's energy being emitted in the visible spectrum. If a 75W 130V bulb uses a greater proportion of it's energy emitting heat rather than light that could be why we noted fixture problems. Lifetime on your 230V bulb should be in decades and if high in heat,low in light just perfect for the application. Pure guess on my part though, and going against at least part of Wiki's undoubted veracity.

I am not an engineer, nor do i play one - happy when lights go on when a switch is thrown.

 

[REWahoo]

... they exactly match the existing incandescent bulbs (which are unscrewed so that they are off):

Al, I think we need a new word to describe you. I vote for "freap" - more than frugal yet not quite cheap.

 

[RustyShackleford]

Nice selection of bulbs of all kinds, including CFLs, at Light bulbs, Rope Lights, Halogen and Fluorescent bulb - 1000-Bulbs - The Light Bulb Superstore ...

 

[ERD50]

W/ regard to 130V bulbs, we used them in a number of applications but no longer do. They create much more heat - ...

Calmoki: I'm surprised the 130V bulbs would cause excess heating of the fixture compared to 120V bulbs. Any theories on this?

I'm guessing, and will gladly defer to a lighting engineer. But. Wiki says this: // surface area stuff// Pure guess on my part though, and going against at least part of Wiki's undoubted veracity.

I am not an engineer, nor do i play one - happy when lights go on when a switch is thrown.

Wiki worded the surface area thing very poorly. But after some more doodling (ala the tire rotation thing ), a lower voltage bulb will have less surface area relative to it's size, so I think more of the heat stays trapped inside the filament.

A lower voltage bulb of equal watt consumption will need to have a shorter and/or thicker filament (assuming all other things equal, same filament material, etc). Lower Voltage, same Watts means lower Resistance, so R must come down, therefore thicker and/or shorter filament. So, let's assume same length filament, and some easy numbers:


100V, 100 W bulb: Requires 1 Amp, and a 100 Ohm filament.

50V, 100 W bulb: Requires 2 Amp, and a 25 Ohm filament.

A 25 Ohm filament is 1/4th the R of a 100 Ohm, so it requires 4x the cross sectional area (keeping the length and material the same). Increasing the Cross-sectional Area by a factor of 4 only increases the circumference ( or radius or diameter, and therefore the surface area) by a factor of 2.

So the low voltage bulb does have more total surface area, but a lower surface to volume ratio. The only part that can give off light is the surface, so I think what happens id the heat generated inside the center of the filament is just trapped.

Or, if the filament was 4X shorter, it would have less surface area (hey that was easier, too bad I thought of it second!)

A secondary effect is that generally, low voltage bulbs have shorter filaments ( or a combination of shorter & thicker), so more of the filament is close to the stand-offs. The standoffs absorb heat away from the filament, so that part does not incandesce. Also, the thicker filament will conduct more heat to the standoffs, also lowering the ability of the filament to incandesce. So when a high voltage bulb is run at its design voltage, it can be more efficient than a low voltage bulb run at its design voltage.

Bring on the LEDS!

Wait a minute - what was the question? .... Oh yeah, a 130V bulb running on 115V, producing the same lumens as 115V bulb on 115V will be less efficient and therefore hotter. Once you lower the voltage from the design voltage, the efficiency is going to drop. So, he was probably replacing 40W 115V bulbs with 60W, 75W or 100 W 130 V, or something along those lines. So, more heat generated.


-ERD50

 

[SteveL]

ERD50 is correct, except that Ohm's Law is for direct current. You have to convert AC to get a direct current voltage equivalent. The easy way to do this is to multiply the AC voltage by .707. This gets you close to the correct voltage to calculate amperage.

 

[JOHNNIE36]

If anyone out there is interested, the thing that a few years back got me going on CFL's was my wife's constant complaining about how hot it got in her bathroom when she was blow drying hair and putting on makeup. It was all those incandescent bulbs--so I changed them out to CFL's and she hasn't complained since. Thinks I'm a genius!

 

[NW-Bound]

ERD50 is correct, except that Ohm's Law is for direct current. You have to convert AC to get a direct current voltage equivalent. The easy way to do this is to multiply the AC voltage by .707. This gets you close to the correct voltage to calculate amperage.

For our convenience, AC voltages and currents are usually already quoted as rms (root-mean-square). This means that the common 115VAC is really 115VAC rms, not 115V amplitude or 115V peak. It has a peak voltage of 115*sqrt(2)=162V. This means that it swings sinusoidally between -162V to +162V, not between -115V to +115V.

100V, 100 W bulb: Requires 1 Amp, and a 100 Ohm filament.

50V, 100 W bulb: Requires 2 Amp, and a 25 Ohm filament.

So, if we want to pick on ERD50, all we need to add is the word rms as follows, and he is still correct.

100Vrms, 100 W bulb: Requires 1 Amp rms, and a 100 Ohm filament.

50Vrms, 100 W bulb: Requires 2 Amp rms, and a 25 Ohm filament.

 

[mathjak107]

25 watt bulbs are much more expensive than 40 , they sell very few in comparison

 

[ERD50]

I go into Home Depot last night to get some light bulbs for the house.

$2.97 for a 2 pack of GE soft white 25W bulbs, and

$.88 for a 4 pack of GE soft white 40W bulbs.

I don't know! Maybe GE sells more 40W bulbs (than 25W bulbs), bringing the price down? Doesn't sound like a likely explanation but I can't think of any other.

25 watt bulbs are much more expensive than 40 , they sell very few in comparison

I've noticed this too and it is odd. They definitely sell more 40/60/100W bulbs than they do 25W bulbs, and that explains part of it. But that is a big delta. Maybe 40/60/100W light bulbs are sold as a "loss leader" (or at least "low profit" leader?) to get people in thee store and buying, but they feel they don't need to do that with the less popular sizes?

A 25W bulb is just a variation of a 60W bulb, it's not like they really need to charge a multiple to re-coup their engineering, or capital expenditures, etc. You don't pay 2x or more for a car in a less popular color. These are not special or custom orders, just less popular variations.

In fact, this has had a negative effect. I have a few places where I just need some light, 25 or 40W would be fine. But I look at the price and get the 40W - I'll never recoup the savings in electricity with the price delta. And before you say CFL - these are on an electronic timer that can't use a CFL. I feel bad "wasting" energy, but I'm deciding to make it a financial decision.

-ERD50

 

[ERD50]

So, if we want to pick on ERD50, all we need to add is the word rms as follows, and he is still correct.

100Vrms, 100 W bulb: Requires 1 Amp rms, and a 100 Ohm filament.

50Vrms, 100 W bulb: Requires 2 Amp rms, and a 25 Ohm filament.

Well, as long as this thread came alive again, I'll respond to this. I started, but my post got eaten up during the maintenance problem, so I dropped it. Wasn't that important. Anyway...

Just to be technical about our technical discussion , there is nothing 'incorrect' about saying 100V x 1A = 100W. Since the descriptor was not specified, it would be assumed (convention might be a better word) that they are all the same units. You would not mix RMS and Peak (for example) in the same equation w/o specifying them.

So:

100V RMS x 1A RMS = 100W RMS
100V DC x 1A DC = 100W DC
100V Peak x 1A Peak = 100W Peak
100V Peak-to-Peak x 1A Peak-to-Peak = 100W Peak-to-Peak

are all as true as

100V x 1A = 100W.

As a reference point, the venerable Ohms Law states simply that E=IR. It does not specify RMS, Peak, etc. And if Georg Ohm had it wrong, I've lived my adult life as a lie!

-ERD50