4000K vs 5000K

The short version: 4000K is the coolest light most homes can live with, and 5000K is a working light. The line between them is not quality, it is job.

It does not change how much light you get. Lumens are lumens. An 800 lumen bulb at 4000K and an 800 lumen bulb at 5000K put the same quantity of light in the room. Cool light reads as crisper, which people report as brighter, and that misreading is how rooms end up cold and still dim. If a room needs more light, it needs more lumens - the method is in how many lumens does a room need.

It changes what the room says. 4000K still reads as white. 5000K reads as daylight, and daylight indoors after dark is the signal your body gets from a supermarket aisle rather than an evening at home. That is the whole objection to it in living spaces, and it is a real one.

It changes how much CRI matters. Cool light exaggerates a poor spectrum: under a CRI 80 bulb at 5000K, skin and wood look flatter than the same CRI 80 bulb at 2700K. If you are going cool, go high-CRI with it - the case is in best high-CRI LED bulbs.

It changes nothing about glare. A bare 5000K bulb in your sightline is unpleasant because it is bare, not because it is cool. That is a shade-and-aim problem, covered in glare and visual comfort.

Waveform CENTRIC DAYLIGHT A19, 4000K - the neutral white to buy. 800 lumens at 4000K with CRI 95+ and R9 80+ published, which is far above what a neutral-white bulb usually offers. At this color temperature the spectrum is what separates a crisp room from a flat one.
Cons: not dimmable, so it has to go on a plain switch; not rated for enclosed fixtures; and it costs several times what a supermarket 4000K bulb costs.

Cree Lighting A19, 5000K - the daylight bulb for a sealed fitting. 815 lumens at 5000K with CRI 90, dimmable, and listed as good for enclosed fixtures, which most cheap daylight bulbs are not. Laundry rooms and utility fittings are usually sealed domes, and that is where this earns its place.
Cons: 5000K is wrong in a living space, and the bulb cannot tell the difference; 815 lm is a 60W-equivalent, so a big garage needs several or a shop light.

Feit selectable A19, 2700K to 5000K - the way out of the argument. 800 lumens at CRI 90 with five settings including both values on this page, chosen on the bulb before you fit it. If you genuinely cannot decide, buy the decision rather than the bulb.
Cons: the setting is made before installation, so changing it means taking the bulb back out; and a pack of them set to different values in one room is the exact mistake this page warns about.

Lithonia FMLRL 14 in. flush mount - when the fixture is the decision. 1,600 lumens at a fixed 4000K. Integrated fixtures pick the color temperature for you and you live with it for the life of the fitting, which is an argument for 4000K over 5000K in any room that is not a workshop.
Cons: no CRI published; fixed color, so the only way to change your mind is a new fixture; the comparison with bulb-based fittings is in integrated LED vs bulb fixtures.

Decide by the job, then check it after dark. Both values look reasonable at noon with a window open. The test that matters is the room at 9pm.

Keep one value per room. Two whites side by side always makes one of them look wrong. If you are switching a room from 5000K to 4000K, change every bulb in it or none.

Above 5000K, you are buying a tool, not a light. 6500K bulbs exist and have a real use in close color work - Waveform sells a 6500K version at CRI 95 for exactly that. In a living room it is unambiguously wrong.

If the room does two jobs, buy the ability to change. A selectable bulb, or tunable white on a schedule - cool during working hours, warm in the evening - which is the argument in circadian and tunable white lighting.