What is the thinking about LED retrofit bulbs?

Flicker Index

Senior Member
Location
Pac NW
Occupation
Lights
I'm under the impression that fluorescent ballasts put out several hundred volts AC.

Why would a high voltage be easier to convert than 120v?
It has nothing to do with the voltage. If you had 120v AC at 0.5Hz, you would be able to see a light bulb slowly brighten up from zero, dim down again until it shuts off and repeat the whole thing once a second. If it was two LEDs hooked up back to back, you would see one light up, then fade away, then the other polarity light up, fade away and alternate. By definition, alternating current is discontinuous power delivery. There is absolutely no getting around this "power outage" without using capacitor on a single phase power. You absolutely have to have a capacitor in order to keep the light from dropping to zero, or ideally not even close to getting to zero. Lower the frequency, larger that capacitor has to be. The capacitor inside a high quality fluorescent ballast does this already on the 60Hz side and you don't really need to fill the gap on the 40,000 Hz as it is not visually perceivable.

There are capacitorless LED ballasts. Those actually fully blackout at each half cycle, 120 times a second. Traditional fluorescent lights do as well, but unlike LEDs, phosphors on fluorescent lamps have a considerably more afterglow than LEDs and it is enough to significantly reduce flicker.
If you were turning a DC generator with a single phase AC motor, the mechanical inertia of spinning motor and generator are doing the work of the DC link capacitor.
 

winnie

Senior Member
Location
Springfield, MA, USA
Occupation
Electric motor research
Fluorescent ballasts do put out high voltage to start the lamp, but the most important thing they do is regulate the current to the lamp.

The gas discharge in a fluorescent lamp has negative incremental resistance, meaning that as the current goes up the lamp voltage goes down. The ballast is needed to regulate the current.

If you string LEDs in series to get a proper total operating voltage, a fluorescent ballast can drive the LED string directly. I don't know if any commercially available retrofit bulbs work in this fashion or if they still keep driving circuits in the bulb.

Jon
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
I believe there are led's that work with an existing electronic fluorescent ballast. My feeling is that the ballast is just something else to go wrong and have to fiddle with. The T-8 led bulbs last a long time
 

James L

Senior Member
Location
Kansas Cty, Mo, USA
Occupation
Electrician
I believe there are led's that work with an existing electronic fluorescent ballast. My feeling is that the ballast is just something else to go wrong and have to fiddle with. The T-8 led bulbs last a long time
I wired a deli/market last year, and the basement, stairs and storage areas had t8 strip lighting. I used ballast compatible LEDs there because they have a maintenance handyman who knows little to nothing about anything. My thought was if the lamps fail, he'll probably go grab the cheapest t8 tubes he can find, and it'll be fluorescent.
 

olc

Senior Member
I am researching this topic, so this thread it interesting & helpful to me.

Here is a little personal experience:
I put a couple commercial* fluorescent fixtures in my office maybe 20 years ago. The ballast in both went after not to long (say < 5 years). The replacement ballast were from Home Depot probably and still work. A few years ago (3ish) I put in LED replacement lamps and they work great.

On the other hand I I would not see the point of replacing a ballast if you are using LED. May as well go ahead and remove it. I did see an office maintenance crew doing this.


(* I got it direct from a local rep. Kind of a nice wraparound that I used often until I had direct experience with it. That's another story but I ended up just leaving the lens off.)
 

kwired

Electron manager
Location
NE Nebraska
Fair point, for sure

I'm thinking about owners and maintenance men who just see a tube with pins
I've seen owners or maintenance men who just see a tube with pins. It may get replaced with a T8 or T12, whatever they find first. A label won't change anything either. Same people in past replace HID lamps with incandescent then wonder why they don't put out much light compared to what they had before if it does light up - most HPS will. Or if they know it can't be incandescent will put a MH in a HPS or vice versa.
 

James L

Senior Member
Location
Kansas Cty, Mo, USA
Occupation
Electrician
I've seen owners or maintenance men who just see a tube with pins. It may get replaced with a T8 or T12, whatever they find first. A label won't change anything either. Same people in past replace HID lamps with incandescent then wonder why they don't put out much light compared to what they had before if it does light up - most HPS will. Or if they know it can't be incandescent will put a MH in a HPS or vice versa.
I use labels for electricians who might be in there later. The maintenance guy who only sees pins, can't really do much for him. I've seen it plenty, too, where T12s and T8s are mixed together, MH and HPS mixed...those guys are a hindrance to themselves
 

olc

Senior Member
A local college had (at least they did a few years ago) a policy to use fluorescent fixtures retrofitted with UL type C for new construction. I assume for ease of future replacement.
 
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