Why It Was Almost Impossible to Make the Blue LED [video] | Hacker News Reader

Why It Was Almost Impossible to Make the Blue LED [video]

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13 pointsaaraujo0026 comments

When I graduated, my first project was to make a UK LED based wait indicator. The problem was, the standard specified "white" light. At the time while LED's where made using UV LED's and phosphors was used to make it white. This meant that for 100 LED's, the coat would be about £100 just for the LED's. In the end we got the specification changed to include a yellow, (we showed that a tungsten light bulb running at 45vac is very yellow anyway, so it was more a correction in the spec than a change)

While the video at 28:09 asserts "virtually no downsides" to LED bulbs, it overlooks a crucial aspect: light quality.

The quality of light is a critical parameter, typically measured by CRI (Color Rendering Index) or the more comprehensive TM-30 metric. Incandescent bulbs naturally excel in this regard, offering what is often considered 'optimal' light quality. However, replicating this with white LEDs remains a technically complex and costly endeavor.

> However, replicating this with white LEDs remains a technically complex and costly endeavor.

Not really. IKEA sells LED bulbs with quite a nice CRI for €1.99 per two. As I understand it the main trick is not to use the LED light directly, but pass it through a phosphor.

Depends on what quality you desire. Quite nice quality is indeed not costly. But if you need top color rendering quality, such LEDs are still very expensive compared to incandescent bulbs.

The official IKEA specs for [1] says nothing about CRI nor TM-30 AFACT, but I found a Reddit thread [2] that says the CRI is 90, which is indeed quite nice, but not excellent. Also, CRI is flawed, especially for sources below 5000 kelvin (K), so I will buy those IKEA LED bulbs and measure TM-30 out of curiosity. Really good price, so the quality/cost ratio has potential to be impressive.

For most people, CRI 90 is probably fine. I just thought it was important to point out that the color rendering quality of light sources is important and something to verify when buying lighting. It's incredible how the quality/cost has improve for LED lighting over the years, and hopefully it will continue to improve in the future.

[1] https://www.ikea.com/us/en/p/solhetta-led-bulb-e26-450-lumen... [2] https://www.reddit.com/r/BigCliveDotCom/comments/ujdvr4/new_...

As far as I know just high CRI alone as a measurement is only a small part of the story. You can have 90 CRI LEDs that don't have good color output.

What a lovely story and well-explained!

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