This is a good observation and a valid concern regarding the replacement of LED bulbs. You've highlighted several key points: Lifespan and Date Code

You have an 8-year-old bulb from 2017, manufactured in China, with a specific date code. This is useful for understanding the product's age and origin. You know it's rated for 15,000 hours, but you don't know how many hours you put on it.

Efficiency (Lumens per Watt)

You've correctly noted that while technology has improved, not all bulbs are created equal. You've found that the light output is better or equal to other newer LEDs, but more efficient ones do exist.

Ballast and Dimming Compatibility

This is the most important takeaway. You've experienced the critical issue of differing dimming curves due to changes in ballast/driver technology between older and newer LEDs. This is not just a perception; different ballasts have different dimming profiles, leading to inconsistent dimming when mixed on the same circuit.

Analogy to Tires on a 4WD Vehicle

Your analogy is perfect! Just like tires on a 4WD vehicle, mixing LED bulbs with significantly different dimming characteristics on the same circuit can lead to uneven performance and a less-than-ideal user experience.

Emerging Issue with Dimmable LEDs

You are absolutely right that this wasn't a significant problem before dimmable LEDs became commonplace. Now, the proliferation of dimmable LEDs with varying technologies makes bulb selection more complex.

Why is this happening?

LED technology is constantly evolving. The internal driver (often referred to as a ballast, although technically different than traditional ballast) regulates the power going to the LED chips. These drivers control how the LED dims. Older LED drivers used different dimming methods compared to newer ones. There are different standards and methods. They do not all play nice with the other.

Implications and Considerations



Replacing Bulbs

When replacing dimmable LEDs, consider replacing all the bulbs on the same circuit to ensure consistent dimming behavior. Or, replace them one at a time with the same bulb type, or as close to the same bulb type as possible.

Compatibility

Check the specifications of the new bulbs to see if the dimming technology is listed. Some manufacturers might provide information about compatibility with different dimmer switches or other LED bulbs.

Dimmer Switches

Ensure your dimmer switch is compatible with the type of LEDs you are using (LED compatible dimmers are a must). Some newer dimmer switches are designed to be more adaptive and work with a wider range of LEDs, but compatibility is never guaranteed.

Testing

If possible, test a single new bulb on the circuit before replacing all the old bulbs. This will help you assess the dimming compatibility.

Documentation/Notes

Keep track of the brand and model of the LED bulbs you are using, especially if you find a combination that works well.

In summary, you've correctly identified a genuine issue with dimmable LED technology. The changing ballast/driver technology leads to inconsistent dimming performance when mixing different generations of LED bulbs on the same circuit. Your "tires on a 4WD vehicle" analogy is a great way to explain the problem. Flag for review