“To generate.” How well a light renders a certain color is a measure of how well it generates the color which we perceive.
Replacement LED T8 lamp
Replacement lamps are a direct replacement for an existing fluorescent lamp. You pull out the old fluorescent lamp from the fixture, and in goes the LED lamp. This seems like an ideal solution, but its drawback is that the lamp must be able to work with the fixture’s existing ballast. This can be tricky because there are many, many different fluorescent ballasts out there.
A replacement LED lamp in a ballasted fixture will have two separate power supplies — its internal driver as well as the fixture ballast — and each power supply introduces power losses. Keeping the original ballast means an unnecessary power inefficiency. Plus, fluorescent ballasts generally have a shorter lifespan than LED lamps, so you may be dragging a ballast along that is inefficient AND will die before the LED lamp does.
Retrofit LED T8 lamp
Retrofit lamps require that the fixture be modified to remove the ballast, allowing a direct wiring between the lamp in the fixture and the house ac power. The obvious disadvantage is that it requires the cost, effort and knowledge to rewire the fixture. The advantage is that the light pays no efficiency penalty since it only has its own lamp driver and will cost you less in electricity costs, and you’ll never have to replace the fixture ballast. In addition, retrofit lamps are often less expensive than replacement lamps.
T8 tube lamp
A linear lamp, of which the most popular version is the fluorescent tube light. The “T” identifies the shape, which in this case is “tubular”, while the “8” indicates the diameter in eighths of an inch: 8 eighths, or one inch. Since fluorescent tube lights are the most popular lamp in the US – primarily in the commercial, industrial, and institutional space — being able to replace them with LED replacement lamps using the same fixture is a primary goal of the LED lighting industry. The most common version of the fluorescent T8 lamp is four feet long, consumes 32W, and emits 2800 lm.
Source: Designing with LEDs