Flourescent bulb question..

brewerpaul · Post by **brewerpaul** » Sun Jan 20, 2008 6:05 am

I decided to single handedly save the environment by switching the 7 spotlights in our kitchen to flourescent ones. The old ones wasted so much energy that I could actually feel the heat on my face when I stood beneath them.
The new bulbs take a moment to flicker on, which I expected. What I didn't expect was that when they first come on they are quite dim, but after a few minutes they slowly get brighter (never as bright as the old ones, but quite acceptable). If I turn them off and right back on, they come on bright: this only happens after the bulbs have been off for a while and presumably cooled.
We have other flourescent bulbs in the house, but I've never noticed this phenomenon before. Anyone know why this happens?

rebl_rn · Post by **rebl_rn** » Sun Jan 20, 2008 6:46 am

This happens with most of CFL's in my house (most of my bulbs are). It's a little annoying at first, but now I'm used to it. I notice it most in my bedroom, where the overhead lighting is a ceiling fan with 3 bulbs - when I turn on the lights now in there, it seems pretty dim. If I leave the room for a minute or two and walk back in, I'm always surprised at how bright it is in there - it actually is brighter than with the old bulbs.

mahanpots · Post by **mahanpots** » Sun Jan 20, 2008 8:23 am

I kind of like this phenomenom at times, for instance, when I get up in the middle of the night to do whatever, and flip the switch, it's nice to have the light dim at first, or when you come into a dark house after a night out, the same holds true.

Michael

Jerry Freeman · Post by **Jerry Freeman** » Sun Jan 20, 2008 8:39 am

We have the same effect in our house. The recessed flood (or spot; I can't remember which they are) lights in the kitchen ceiling are noticably slower to brighten up.

I believe this is because of the black hole at the center of the galaxy. Either that or dark matter. Either one could cause a dimming effect.

Best wishes,
Jerry

Innocent Bystander · Post by **Innocent Bystander** » Sun Jan 20, 2008 8:55 am

Okay, I thought someone would have responded by now with the actual answer. So here it is.

Incandescent bulbs work on resistance. There's a very fine, very thin filament through which you pass current, and because it provides an obstacle (resistance) it heats up and provides light as well. The filament does take a measureable time to warm up, and you can see this in old-fashioned lightbulbs.

Fluorescent tubes work on Potential Difference. All that's in the tube is a gas, across which you create a voltage difference (like a pressure of current). The starter for fluorescent tubes involves a capacitor, which serves to store this potential difference. It takes time to build up the reservoir of voltage. As it builds up, you can see the light start to flicker, and sometimes you get lines of striations which drift from one end of the tube to the other. I haven't seen this in fluorescent bulbs, but I have spent a lot less time staring at them. On the London Underground, the tube trains often have old tubes where the gas has managed to leak, or the contacts to decay, so there are continual striations along the tube. This can be distracting or even irritating, and can cause epileptic seizures in some people.

Now some bright spark will post a link to somewhere that explains it a whole lot more succinctly than this. Never mind. This was a REAL explanation, from your Uncle Fred.

brewerpaul · Post by **brewerpaul** » Sun Jan 20, 2008 9:39 am

I knew that the flickering and delay in lighting had to do with charging the capacitor, but I still don't see why the bulb starts out dim and then, over a period of a minute or two, gradually and slowly reaches maximum brightness. Maybe in the base of the bulb there's something in addition to the capacitor (a transformer?) that needs to warm up in order to put out the maximum voltage.

susnfx · Post by **susnfx** » Sun Jan 20, 2008 9:55 am

I keep telling myself I'm going to buy fluorescent bulbs, but when I need lightbulbs I stand in front of the display and find myself looking at a price of $1-2 for 4 regular bulbs and $6-7 for 1 fluorescent. I've been unable to afford one yet. Maybe when I win the lottery I can also save the earth. (Yes, I realize they'll save money in the long run--but it makes no difference if I don't have the money now.)

Susan

Jerry Freeman · Post by **Jerry Freeman** » Sun Jan 20, 2008 10:06 am

susnfx wrote:I keep telling myself I'm going to buy fluorescent bulbs, but when I need lightbulbs I stand in front of the display and find myself looking at a price of $1-2 for 4 regular bulbs and $6-7 for 1 fluorescent. I've been unable to afford one yet. Maybe when I win the lottery I can also save the earth. (Yes, I realize they'll save money in the long run--but it makes no difference if I don't have the money now.)

Susan

Try WalMart.

They've made a mission of getting compact flourscent bulbs into as many households as possible, and their prices are the cheapest I've seen.

Best wishes,
Jerry

chas · Post by **chas** » Sun Jan 20, 2008 10:37 am

Sam's club has CFL's pretty cheap, too. Best if you're planning on a wholesale switch, of course, as they're in packs of 8 or 10.

The light in a fluorescent is created by a discharge in mercury vapor. The mercury emits mostly in the ultraviolet; the UV hits a phosphor coating on the inside of the tube, which gives off the visible light. But a mercury discharge is notoriously difficult to start, so there's also a low pressure of sodium in the tubes. The sodium discharge is easy to start and then starts the mercury discharge.

My experience is it takes a few weeks for this long delay in full output of CFLs, which would point to an aging effect rather than something intrinsic in the bulbs. CFLs have electronic ballasts rather than the old-fashioned capacitor ballast. It's possible that there's a burn-in of one of the electronic components. But I think it's more likely the electrodes. The electrodes in discharge lamps like fluorescents actually have very small volumes of molten metal. This stuff is constantly melting, rearranging itself, re-crystallizing, etc. I suspect that after a few weeks, the stuff has rearranged in such a way that when it cools, it's not in an optimum configuration, and it takes a few minutes to re-optimize.

peeplj · Post by **peeplj** » Sun Jan 20, 2008 10:41 am

We have installed some fluorescent lights in our house, but I don't like the quality of light they provide. It is a cold, harsh light and colors aren't true under that light.

Incandescents, for all their wastefulness, provide a much softer, warmer, and friendlier light.

--James

susnfx · Post by **susnfx** » Sun Jan 20, 2008 10:50 am

Most of the lights in my house (including the in-ceiling fixtures, not just lamps) have stickers warning me not to use anything more than a 60-75 watt bulb. I'm nervous about replacing them with fluorescents because I don't know what the equivalent is. I know what the equivalent is in light output, but that's not what they mean--they're talking fire hazard. Sorry to derail the topic, but I've never been able to figure this out. I've never seen this mentioned in any of the articles I've read about fluorescents.

Just found this site that was helpful for info on incandescents:

http://www.energystar.gov/index.cfm?c=cfls.pr_cfls

I guess I just use the equivalent to what I'm using now in watts and hope I don't burn the house down.

Susan

peeplj · Post by **peeplj** » Sun Jan 20, 2008 11:03 am

CFLs produce a lot less heat than incandescent bulbs, which is one of their advantages...a lot of the wasted energy of a conventional light bulb is radiated as heat instead of light.

They also use a lot less energy to emit roughly the same amount of light; your house should actually be much safer with the flourescent lighting than it was with incandescent as far as heat or fire risk.

The main thing is to be very careful with the flourescent bulbs...they contain mercury, and are hazardous to break, and some communities have special rules concerning the disposal of flourescent bulbs because of the mercury.

--James

dwinterfield · Post by **dwinterfield** » Sun Jan 20, 2008 11:30 am

CFLs are now being sold as "warm" bulbs. They are not as nice as incendesents, but they are better the cold bluish CFLs. We have replaced all bulbs that aren't on dimmers (we have lots of dimmers).

We've bought bulbs very cheaply by poking around the bulb displays in Lowe's and Home depot. There are often coupons that offer substantial discounts. On one occaison a coupon offered $10 off a 4-pack of bulbs - limit 6 per household. They had a 4-pack with a $9.99 price tag. I filled out the coupons and obtained $60 worth of bulbs for free. They didn't give me the $0.06 change. The utility companies are behind most of these discounts.

Innocent Bystander · Post by **Innocent Bystander** » Sun Jan 20, 2008 11:48 am

brewerpaul wrote:I knew that the flickering and delay in lighting had to do with charging the capacitor, but I still don't see why the bulb starts out dim and then, over a period of a minute or two, gradually and slowly reaches maximum brightness. Maybe in the base of the bulb there's something in addition to the capacitor (a transformer?) that needs to warm up in order to put out the maximum voltage.

As I understand it, there is a minimum voltage at which the gas will fluoresce, but the operating voltage is slightly higher than this. The capacitor keeps building up a potential difference even while the gas has lit up. So it gets brighter after a few minutes.

emmline · Post by **emmline** » Sun Jan 20, 2008 11:54 am

peeplj wrote:We have installed some fluorescent lights in our house, but I don't like the quality of light they provide. It is a cold, harsh light and colors aren't true under that light.

Incandescents, for all their wastefulness, provide a much softer, warmer, and friendlier light.

--James

Thank you. I was hoping not to have to be the first to say that.
I even bought a sample pack from Amazon of the ones that are supposedly "warm" light.
I have cfls in the ceiling fixture in my son's room which is exactly the same fixture and exactly the same paint as the computer room next door to it, in which I have incandescents.
Big difference, and unpleasant to my eye. The kid doesn't mind.
Beyond that I have only been able to bring myself to use them in the basement laundry area, and outside in the porch light and the lamppost.