I was looking into lighting efficiency recently, wondering just how far things can go before we hit the absolute limit. And from what I found, it looks like there’s not a lot of room left to grow.
More specifically, I found these numbers…
- Incandescent lights: ~5 to 15 lm/W
- Current LED lights: ~50 to ~150 lm/W
- True blackbody radiation source like the sun: ~93 lm/W
- Ideal pure white (blackbody radiator minus invisible frequencies, visible light only): 251 lm/W
- Most efficient light possible, narrow-band green at 555nm: 683 lm/W
So, for a high-quality pure white light with 100 CRI, it seems the limit is 251 lm/W. Going higher than that means sacrificing quality, mostly by decreasing CRI and increasing the green component compared to other frequencies.
The upper limit for “white” LEDs is estimated at 260 to 300 lm/W, depending on how much green tint people are willing to tolerate. Meanwhile, Cree already reached 303 lm/W back in 2014, at a power level of 350mA and CCT of 5150K.
In the past couple decades, there has been a huge and exciting explosion of LED lighting tech, dramatically improving lights by a factor of 10X or even 20X in a relatively short amount of time, mostly by switching from incandescent to LED. It has been a good time for everyone involved.
However, it looks like the party is coming to an end.
There are definitely still significant gains left to be accomplished. We could still double the efficiency of average lights. However, that’s about it. There will probably never again be a rapid explosion of progress like what happened in the past couple decades. We could see a 2X or maybe even 3X improvement over time, but nothing like the 10X or 20X increase we already experienced. What’s left is a matter of diminishing returns.
I think many of us have probably already noticed this, given how many lights don’t use the latest tech. Instead of XP-L2, we’re using the older XP-L HI. Instead of XP-G3, XP-G2 looks better. People happily forego new LEDs like SST-20 and SST-40 in favor of old “obsolete” items like 219B, because the new stuff looks too green.
And then of course there are also losses in the lens, the reflector/optic, the driver, the wires, the springs, etc. Each one is small, but it adds up. So instead of 251 lm/W, the practical limit for a pure-white flashlight may be more like 200 lm/W.
That’s a big improvement over my 219B lights with their measly ~70 lm/W. And a big improvement over my XP-L HI lights at ~100 lm/W. I don’t really need my lights to be brighter, but I like the thought of getting 2X or 3X as much runtime per battery charge… even though I rarely ever need to charge anyway.
So… that’s what appears to be ahead in the future. We’ll keep seeing improvements for a while, but each year will probably bring less and less exciting changes until it all seems fairly mundane… and we’ll move on to other exciting things.