When were LED displays invented?

 "When were LED displays invented?" Let me start by recalling the previous conversation. They wanted to know what LED displays are, and I explained their structure, types, features, and applications. Now they're asking about the invention timeline.

First, I need to ensure accuracy. I remember that LEDs themselves were invented in the 60s, but LED displays came later. Let me verify the key milestones. Nick Holonyak is known for creating the first visible LED in 1962. That's a starting point.

Then, when did the first actual LED displays appear? Probably in the 70s. I think the first practical LED display was developed by James P. Mitchell in 1968, but it was monochromatic. Red LEDs were common first. So early displays used red LEDs, like calculators or digital watches.

Wait, the first commercial use might be in the 1970s. For example, the HP-35 calculator in 1972 used LED displays. Also, the Monsanto Company and others started producing LED-based signs around that time.

Moving forward, the development of blue LEDs in the 90s by Nakamura, Amano, and Akasaki was crucial because it allowed full-color displays. That's a Nobel Prize achievement in 2014. So blue LED invention in the early 90s enabled RGB combinations.

For large displays, the timeline might extend into the late 90s and 2000s as technology improved. Outdoor LED billboards became more common then.

I should structure the answer chronologically, starting with the invention of the LED, then early monochromatic displays, the introduction of blue LEDs, and the evolution into modern full-color displays. Also, highlight key contributors and applications over time.

Need to check if there's any confusion between LED displays and OLED. The user's previous question was about LED displays in general, so OLED is a different technology. Make sure to clarify that if necessary, but the focus here is on traditional LED displays.

Also, mention the impact of each development. For example, blue LEDs made full color possible, leading to today's video walls. Maybe include specific years and examples like calculator displays, early digital watches, and when large-scale LED screens became feasible.

Avoid technical jargon but ensure the key points are covered. The user might be interested in both the historical milestones and how the technology progressed to what we see now. They could be a student, a professional, or just curious. Tailor the answer to be informative yet accessible.

Double-check dates: Holonyak in 1962, HP-35 calculator in 1972, blue LED in early 90s, Nobel Prize in 2014. Yes, that's correct. Also, mention the transition from monochrome to full-color and the expansion of applications from small devices to large screens.

Make sure the answer flows logically, starting from the invention of LEDs to the development of displays, highlighting key dates and technological breakthroughs. Keep it concise but thorough, as the user likely wants a clear timeline without unnecessary details.