My office overhead lighting currently uses fluorescent bulbs. For ~5 minutes after turning them on, lights will flicker. I diagnose this as a weak ballast.

If I insert LED retrofit bulbs into this setup am I likely to solve the temporary flickering problem?

  • I installed the LED bulbs and two years going there has been no problem Jun 19 '19 at 16:13

Your ballasts are shot. It's time to upgrade one way or the other.

I am all about light quality (CRI and flicker). I tinkered with LEDs but finally went with T8 real fluorescents because the quality is better. Absolutely wonderful, it's like night and day (I left the storeroom in the old tubes, the room looks horrid.)

Real Fluorescent Tubes

This is the best light money can buy, and the price is very reasonable.

You will want to change from traditional T12 tubes to the new T8 size. They fit in the same sockets but you must change the ballast to a T8 type. You want to anyway; your old ballasts are the problem!

enter image description here

First, your ballasts. That is a module which limits current to the tubes. The old ones were very simple and stupid. They tend to "soft fail" with annoying flicker and poor light, and burning out tubes too fast. New electronic ballasts drive the tubes perfectly for excellent light with no flicker, even in cold. Almost any modern ballast will do fine; you can get dimming ballasts if you really want that. You will need to open up the fixtures and change the ballasts. However you'll be glad you did.

There's a glut of new T8 ballasts on eBay and Craigslist dirt cheap, because people are buying new fixtures and promptly switching them to LED. Or they're $13-20 retail.

enter image description here src

Fluorescent tubes. Top: obsolete T12. Middle: new T8.

Tubes. Choose carefully, don't grab the first random hardware store tube. You choose in three categories:

  • Length obviously, and Size: T12 vs T8 (you must match your ballast)
  • Color temperature (blueness/orangeness), traditional fluorescents are 4100 "degrees kelvin" which is fine.
  • Color Rendering Index (CRI), which is 0-100. Don't buy anything less than 87 CRI.

I just bought a ton of Sylvania Ultra Vivid 90CRI for $2 each. My shop looks fantastic. You can get as high as 98CRI in the $7-12 a tube range, but you don't need to. Just to compare, I left my storeroom in the mid-1990s T8 tubes and wow, what a difference!

LED replacement "tubes"

Everyone's flocking to this technology because it has hit the "price point" - I see even Sylvanias as low as $6/tube. However the cheapies sacrifice CRI to hit the price point -- and you really want CRI because that's what you have to look at all day. Like I say, my shop makes me want to work in it.

I haven't found any reputable makers of 90 CRI LED tubes. Many won't even state the CRI, which means you better run! Sorry but as a purist, with 90 CRI in my shop at affordable prices, I think LED fluorescent replacement tubes don't compete. (Other LED products are great!) Now here are some things to watch out for.

enter image description here src

Power on one end. Those little chips can be harsh.

  • You really want ballast-bypass aka direct-wire LED tubes. "Plug-n-play" LED tubes are bad news; they require a ballast. (Say what!?) Remember, your ballasts are defective. So let me get this straight, I must install a modern ballast of the subtype the tube needs (instant-start differs from rapid/programmed start) - why not just use a real tube for 1/4 the price and get better light? /facepalm So yes, if you do LED, do direct-wire LED and remove the ballast since yours are dead anyway.
  • You have to worry about shorting lampholders. Instant-start ballasts don't use the filaments in the ends of the fluorescent tube, so they use lampholders (sockets) that short out the two pins on each end. Trouble is, most LED "tubes" want 120V across those pins. You might need to change the lampholders. You can find LED tubes which feed 120V from opposite ends; those don't care. I personally think it's crazy to stick 120V across end pins made for 10 volts.
  • LED light is very directional, the raw LED chip only gives about a 140 degree spread. Most of the time, that works hugely in your favor, as you are not wasting energy lighting up reflectors (which don't work all that well). For some crazy reason, a lot of builders are "corn-cobbing", arranging the LEDs all around so the tube lights up 360 degrees. This isn't even stupid. Avoid those.
  • The LED emitter chips can be harsh on the eyes, so a "tube" which has a bunch of exposed chips will be harsh and distracting. On the other hand, if it has a cloudy diffuser, that will waste light by scattering it places you don't need light. If you have the typical fluorescent troffer with a transluscent cover, (that is actually a lens), that is fine.
  • Dimming: no, no, just no. Affordable LED tube replacements are just not made for dimming. You may find ones that are, but they won't be cheap, and they may be problematic to hook up since offices don't use home dimming technology. The most successful way to get dimming in an office is dimming ballasts, actual fluorescent tubes, and compatible dimming controls, as discussed in my first part.

enter image description here src

The LED strip method

I have also converted a troffer to LED by removing all the tubes and adhering LED strips cut to appropriate length. A 5-metre roll of 3528 LED strip gives about the same useful light as two T8 tubes. I used a top tier 12V LED power supply of the same dimensions as a ballast, so it clipped right in. We leave it on 24x7 as a security light, and it's run perfectly for 5 years despite being a $7 cheap Chinese LED strip. CRI is terrible of course.

I mention this method because it opens up a wide variety of options, including RGB strips, warm/cool blending, infinite dimming, integral 12V emergency lighting, etc. If you simply wanted 80CRI 4100k light, this method won't save you any money. The reason to do it would be the versatility. You could have the coolest office on the block.

The LED strip approach can also co-exist with actual fluorescent lights in the same troffer. Leave all the tubes in place and stick the strips between.

  • I agree with the use of t8's and i love them, but i use the kind that does not need a ballast, direct wire. If you are going to change over and and enjoy the the energy savings of LED then why power a ballast when it is not necessary.
    – Alaska Man
    May 25 '17 at 18:44
  • @Alaskaman I may have been unclear. I recommend electronic ballasts because I recommend staying with actual fluorescent tubes, because the light is better. I've been an early adopter of LED tech, it's just I don't think fluorescent replacement tubes are there yet. May 25 '17 at 18:51
  • Thank you, this is very helpful. I'm in a short-term lease office and my landlord barely keeps the bathroom stocked with paper. So this really helps review all my available options! Jun 6 '17 at 14:00
  • In that case I would just swap ballasts to a modern one, and continue to use the same fluorescent tubes. A ballast is $15 new, and cheaper on eBay. Jun 6 '17 at 15:08

LEDs are not susceptible to the sorts of startup flickering that affect fluorescent tubes.

However LED units are susceptible to other types of flickering caused by dimmers, smart-switches or other types of device in the circuit.

Your best chance of eliminating flicker is to remove the ballasts, then fit a good quality LED fixture - ideally one that tolerates most dimmers.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.