I intend to replace an old and large population of T12 flourescent lights with T8 LEDs: direct wiring. The ballasts are $15 a piece (2 required per fixture) and it would seem that a 4 X $10 direct wire LED bulb is a better choice because of the labor to replace future ballasts is high.

That being said, I would like to understand what color is in the current population and would like the LED to match the population so that the phasing in of the LEDs is seamless.

Is there a clever (simple) method to assess the color?

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I bought a contractor pack of T12 fluorescents (4100K): is this the 4100K the common standard for fluorescent lighting

  • If you can read the printing on the end of the lamp look for CW... Example F40T12CW or F34T12/cw/eco ... CW = Cool White = 4100K if you find a different code without CW tell is what it is... For example F40T12SP3500 which is a 3500K bulb
    – Tyson
    Jun 29 '17 at 23:27
  • You can buy 4-lamp electronic ballasts, and you should be paying well over $15 for a ballast unless you're getting the $2-3 new-stock pulls off ebay, which is my preference. Always buy quality brands if you value your time. I don't have a lot of faith in the $10-tier LED replacement "tubes", and their CRI is not up to where real fluorescent tubes are. I'm sticking with real fluorescent, except in archives where we don't want UV. Jan 17 '18 at 21:07

The temperature will likely be printed on the bulb somewhere. Take a couple out and check, and they are all likely the same. If not, you can compare the color to an image like this:

bulb temperatures

There is no "standard" for fluorescent lighting, as they come in a variety of temperatures. That said, fluorescent bulbs are more traditionally associated with the institutional bright white light, which would put them on the higher end of the temperature scale (closer to 6700K).


If you have a smartphone, look for an app that leverages the camera to give you color temperature.




Generally speaking, 4100K has been the traditional standard for fluorescents, with some 3500k seen here and there. If you bought 4100k tubes and they match, that's your color.

It really isn't any big deal to mix colors during a transition. The point is, finish with the color you want. If you don't know what you want, consult an expert because this is a big expensive project - get it right.

Your Color Rendering Index (CRI) on older tubes is probably in the 50s or 60s. The new T12 tubes you just bought will be at least 80, commonly 87-91, and possibly as high as 98. I personally love them. LED replacements can't get to that CRI yet, and I'm happy to have 90+ CRI real fluorescents.

Make sure your ballasts have two wires going to each end of each fluorescent tube. If there is only 1 wire, then the fluorescent lampholders (tombstones) are surely "shorting lampholders". Those will not work with LED "tubes" which take hot+neutral from the same end of the tube. I don't know why you posted that pic, but that describes same-end types. They won't play with shorting lampholders. Shop carefully for LED "tubes" which take hot+neutral on opposite ends of the tube.

  • Good electrical comments regarding non-shunted tombstones. The pic is from the pdf instructions of the hyperlink. I will religiously follow the wiring instructions provided with the purchased LED bulbs
    – gatorback
    Jun 30 '17 at 3:23

4100K is common for T8 fluorescent lights. It gives of a more bright blue hue light. Some people prefer around 3500K for a softer better color rendition. It's really all about preference and use.

  • This doesn't explain how one would determine the color of a tube. It maybe should've been a comment on the question.
    – isherwood
    Jun 30 '17 at 13:22

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