# how can i safely limit the output of a cfl?



## nitebrite (Nov 9, 2004)

hi all.

i bought a very espensive self ballasted cfl from "ott".
i wanted their best bulb. however the best bulb is 20 watts 1000+ lumens. it is blinding me in my reading lamp on top of me. i want more like 600-700 lumens out of it. i think dimming it with a triac would be asking for big trouble. i tried taping part of it with white electrical tape. but that ruined the spectral distribution of it.

is there some way i can limit the current to the fixture or otherwise get it down to less than 700 lumens maintaining it's intended light quality without killing it prematurely?

thank you,
nitebrite.


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## Wim Hertog (Nov 9, 2004)

I think the only thing you can do is trying to put a neutral grey gel filter in front of the reading lamp.This will reduce the total light output without changing the spectral distribution too much. Controlling the light output by limiting the current is not possible without changing the ballast construction....

Did you pay $50 for this lamp (listed on their website)? We (Flanders Lighting Solutions) are developping a full spectrum CFL, 5200K and CRI 92. It will be launched in Belgium somewhere next month and the specs are equal to the ottlite. Suggested retail price will be 10 euro (thats $12)!!


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## nitebrite (Nov 9, 2004)

yeah i did pay that. stupid,eh? ahh well. the light quality is as good as cfl gets. however! the construction of this lamp is trash. i wonder how long it will last.

well the good news is, i can actually bring it back if i want! bought it at department store that allows returns on any item.

but if i am to do that then i need someone to reccomend what i really wanted in the first place!

11-15watt cfl 5000-5500k, 90+cri. spectral distribution as good as cfl can offer. electronic ballast(either in the fixture or the lamp itself is ok). it must be available at retail in the usa. price doesnt matter(within reason).

i have real good quality pl/s type lamps(light quality is good). however the ballasts for these preheat lamps always suck(magnetic or worse, capacitive). so i won't be using these. verilux and sunter etc are cri only in the mid 80's and are around 6500k. so i don't like those at all.
solux is great except for one huge problem! it is halogen, so it is mostly just a great room heater(terribly inefficient).

thanks,
nitebrite.


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## Wim Hertog (Nov 9, 2004)

Check out the panasonic genIV CFL´s. Their 5000K version has a CRI of 88, which is very good for a CFL. The max CRI I´ve ever seen for a CFL is 92.8.

https://secure.tcinternet.net/buylighting/shoppingcart/panasonic.html

and for the specs:

http://www2.panasonic.com/webapp/wcs/stores/images/Content/Lighting/genIV.pdf

Does your ottlite CFL has an instant start ballast or a preheat one (preheat takes about 1 second to light after flipping the switch)?


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## nitebrite (Nov 9, 2004)

the one i am using right now has electronic instant start.
that is all i will use right now. the pl/s lamps can be good lamps but the ballast technology that runs them is from the stone age and sucks.

the panasonic does not have high enough cri. to match paint(which is what i am using this one for) you must have cri 90+. the difference between 90 and 95 cri in a cfl is negligable. however to match paint it must be over 90 no matter what. the spectral distribution of cfl is very spikey. but i don't mind that. ever see the hot spot of the solux on the paint swatch? great light but it's still a tungsten no matter what that guy says. so i like cfl. not to mention it is way more efficient.

i just found a lamp with a (guarenteed) cri of 5800-6100. 5000 nominal. it is nice when a company is realistic and does not claim their cfl will hit a dead on kelvin temp.
that one is at a higher temp then i prefer but they claim they use a 5 phospher with a proprietary coating to make it 'better' than the ott. and it is 1/3 of the price! if i can find one i will go try it and report back. at $12.95 lots of people could try it. for a $50 lightbulb you got to really have a reason to buy that i would guess.
case in point(this is funny), when i bought it an old lady at the store says "oh lord! your register is broken! i hope it don't ring up my scarf that high!" lol.

nitebrite.


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## Wim Hertog (Nov 9, 2004)

<great light but it's still a tungsten no matter what that guy says>

Filtered tungsten is the most perfect artificial daylight you´ll ever find. If you use a good filter, the CRI will be 99-100! This is because the source (halogen lamp) is a blackbody radiator and has by definition a CRI of 100.

What´s the CRI of the 5 phosphor CFL you mentioned? 

Normally, the more different phosphors they use, the better the color rendering will be, but efficiency will drop. This is because the phosphor has to fill gaps in the lamp´s spectral output in areas (for example red) for which the eye is less sensitive to. 

12,5 dollars really is a fair price for such a lamp! Let me know your opinion once you get it!


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## brickbat (Nov 9, 2004)

Self-ballasted CFL? I assume you are referring to a CFL with an integral electronic ballast in the base? 

I've had surprisingly good luck dimming them with a Variac (variable transformer.) For example the ones in my desk light fixtures (13W, made by Commercial Electric - not advertised as a dimmable model) operate quite nicely down to about 60V, at which point their output has dropped by more than 50%. Going below 50V causes them to extinguish completely. For starting anything below 70V is iffy.

No manufacturer I've seen condomes this, but so far, it seems to work well.

However, you may see CRI/CCT shift. To my eye, these lamps look slightly 'cooler' (higher CCT) as I reduce the voltage.


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## nitebrite (Nov 11, 2004)

i have found that the quality of the light changes drasticaly if i dim a non-dimmable unit. also i have only seen triacs as wall or cord switches. this will either destroy the ballast instantly or in three weeks. the ballasts that are dimmable(ge,sylvania) use a third wire that senses the voltage drop and starts the bulb hotter via discharging a capacitor.

as for the $12.50 daylight(uk) comapny bulb. it is the best bulb i have ever seen anywhere! lucked out this time because i had to drive 3 hours to get it! the claimed cri is 90-93. it is 11 watts and has rather low output which is what i wanted. they also make larger wattage bulbs. the build quality is superior to any cfl i have ever seen! you would have to actaully see one to see what i mean. the bulb is designed different than any other cfl mainly to protect the expensive bulb for shock. when i showed up at the store the man put the bulb next to an equivelant ott bulb. there was no comparison! the daylight hands down won. and it is 1/3 of the price. shame on you ott(for the absurd price).

the ballast does not hum either. the ott does.

keep in mind that this bulb is right around 6000k if not slightly over. looking at only the bulb looks very blue. however everything it shines on is presented in white light. meaning crystal clear reprensentation of colors!
it is $12.50 well spent i think.

i was told by an expert that the color temp(within reason) of a bulb does not promote/impeed the color rendering ability of the bulb. the spectral distribution and cri is what makes a bulb acuratly reproduce colors he says.

ansi specification for daylight is 6500k. over 6000k i find it hard on the eyes. but my aquarium lamps are 15000k and look amazing shining into the deep water in a large tank.
for room lighting i prefer 5000-5500k. this bulb was not availble that way. so i'll have to live with it. nonetheless it's output is true and exact. 
i have this rare cat(pet) that has colors you do not usually see on a domestic cat. when she jumped up on the table next to the light. i said to her, "i knew you were pretty but you look magnifacant under that light!"


nitebrite.


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## jtr1962 (Nov 11, 2004)

[ QUOTE ]
*nitebrite said:*
i was told by an expert that the color temp(within reason) of a bulb does not promote/impeed the color rendering ability of the bulb. the spectral distribution and cri is what makes a bulb acuratly reproduce colors he says.


[/ QUOTE ]
That's pretty much true. Technically, I think 5500K is the most balanced color temperature, meaning that the distribution on either side of the 555 nm peak is even. Other than that, anything from about 4500K to 6500K won't be horrible. If you deviate too far from the ideal of 5500K then you _do_ get color distortion even if you have a CRI of 100. Incandescent lighting is the most notable example of this. The spectral distribution is heavily weighted towards the red end, and there is no real white either. Colors never looked natural to me under incandescent.

BTW, I've found that some magnetic ballasts can be dimmed to about 50% using a standard triac lamp dimmer. A Variac will work with both electronic and magnetic ballasts down to at least 50% also, and in some cases quite a bit lower. However, I have yet to see a lamp dimmer based on a Variac. It would be too bulky and expensive for starters. It should technically be possible to make an electronic ballast which works with a standard lamp dimmer. You simply use an full-wave bridge and filter to get a supply voltage equal to the peak AC voltage. You then have a circuit to read the duty cycle of the triac output and adjust the ballast to drive the lamp(s) accordingly. If more people used linear fluorescents instead of incandescents in their homes doubtless a ballast like this would already exist. Current dimming ballasts require an extra wire and a special switch. This makes retrofitting existing installations cumbersome.


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## brickbat (Nov 11, 2004)

[ QUOTE ]
*nitebrite said:*
i have found that the quality of the light changes drasticaly if i dim a non-dimmable unit. 

[/ QUOTE ]

OK, so why are you asking how to limit the current to your lamp?


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## nitebrite (Nov 12, 2004)

brickbat: i was asking if it can be done without damage and maintaining the quality of the light. just read everything i said. you said yourself that it changes cri/cct.

i was looking for a solution that i may not have known about.
i concure 100% with everything jtr1962 has said.
i have a variac and can dim the bulbs with it. however i need that for electronics troubleshooting and can not tie it up as a $400 lamp dimmer. brickbat, you get a cheap variac for a lamp dimmer somewhere? i already knew a triac couldn't do this reliably. i was looking for another answer. i guess there is no other answer though.
i also mentioned the 3 wire ballast(ge 2d for instance). it fires the bulb at full current and then almost instantly drops it to set level. integral ballast cfl's don't do this yet. i have heard of the dimmable integral ballast cfl's blowing when dimmed below 20%. the package should say this since most triacs dim to less than 10% and are not preset.
there exists no premium quality full spectrum integral ballast cfl that is rated to be dimmed.

anyways, as i said i found a bulb that met my needs in this instance and am quite happy with it.
it would have been nice if i could "crank it up" and get more light when i wanted. i have found the best aproach to room lighting is multiple types of light sources in multiple locations. so this little bulb just factors into my equation anyways.

thanks,
nitebrite.


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## Wim Hertog (Nov 12, 2004)

If you dim a CFL (integral ballast type) with a variac, you WILL damage it. When the input voltage of the ballast drops, the output voltage drops also. The voltage drop causes the electrodes in the lamp to cool down and a lot of electrode material will sputter on the inside of your lamp. A very short lifetime is the result because all the emissive material from the electrodes will be gone.


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## nitebrite (Nov 12, 2004)

so i guess the bottom line is: if the manufacturer states it is not dimmable, it is not dimmable! there are lot's of things us hobbiests do to modify/improve stuff. looks like we are out of luck on this one. glad i got my 11watt bubl i like then.


nitebrite.


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## turbodog (Nov 18, 2004)

Would someone read my thread @ 

http://www.candlepowerforums.com/ubbthreads/showflat.php?Cat=&Number=760594&page=0&view=collapsed&sb=5&o=31&fpart=&vc=#Post760594

and chime in if you can help.


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## mdrejhon (Nov 18, 2004)

Dimming a CFL is done for handheld computer backlights (modern PalmPilots and PocketPC's)

So it is possible to dim certain kinds of CFL. But what kind of CFL, and what method of dimming to use?


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## NewBie (Nov 18, 2004)

The type that are in displays are CCFL, a different technology. This is done by PWM, and paying close attention to the strike, to prevent the bulbs from redepositing the cold cathodes on the walls.

The larger fluorescent bulbs with an external ballast are easy to dim also, they are technically HCFL, and you can buy external ballast versions that are meant to dim the bulbs, I've dimmed these also, with homebuilt ballasts via the PWM mode also. On mine, I've ran them at 75kHz, to reduce the size of the magnetics, then PWM'd them at 300Hz. I've been able to achieve 1000:1 dimming ratios.

Also, International Rectifier makes a chip that is found in alot of external dimming ballasts.


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