Comment by posterboy | Hacker News Reader

Comment by posterboy | Hacker News Reader

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> 1. Lots of LEDs flicker.

No, the diodes don't, the drivers do. You are speaking to a technical audience ;)

> means that they do not emit light in certain frequencies causing objects to look dull/gray. Most LED lamps have a Ra value of 80, meaning that they emit on average in the 80% ...

Hardly. It means that they reproduce a set of 8 or 16 fixed frequencies from the ral pallete. It doesn't cover anything inbetween so it's just a rough rule of thumb. It doesn't cover colors in the far red (or was that violette on the other end of the soecteum?) at all.

Overall, overexposure of some frequencies, arguably to appear brighter and fuller, has damaged musuem pieces--Radiation stress, really. All they can do now is individual tests with photometric instruments, because they can't trust CRI. Same for horticultural lighting, which hasn't really taken of anyway.

Edit: Some manufacturers publish reference curves in the datasheets for their emitters, however I don't know how accurate these are under varying conditions and across batches.

Having made a cheap DIY spectrometer[1], I found the spectrum of LED around my house quite good, not completely smooth as sunlight, but smooth enough (you can gain some efficiency for not being totally smooth by better matching eye receptors). It's a far cry from fluorescent spectra that have extremely sharp concentrated spectra (and I suspect the risk from narrow spectra of causing biological damage is greater, since it could in theory disrupt very efficiently some molecular energy transition that happens to be well matched with that frequency).

[1] See e.g. https://ocw.mit.edu/courses/electrical-engineering-and-compu...

https://lavinia.as.arizona.edu/~mhammer/outreach/cdSpectrome...

(diffraction spectrometer from used CD/DVDs, very easy to make, and it costs ~$0)

If you want to check for flicker, there is a great app called VISO Flicker Tester

Unfortunately the app seems to be broken on iPhone 8+. Fails with "App could not detect camera."

It doesn't detect the camera on my iPhone :(

Could you explain what you mean by ‘disrupt molecular energy transition’? Would be interested to know.

I'm not an expert, so take it with a grain of salt.

Electrons in molecules have discrete energy states they can occupy, per quantum mechanics (the discrete set of wafunction solutions)[1]. Consequently they can only transition between states by absorbing or emitting photons of specific energy values (I believe it doesn't have to be exact due to scattering and various QED dynamics, but it has to be very precise). If your molecule is exposed to broadband light, a few photons will match those ionization energies, however the quantity should be small[2]. If your light source contains peaks though, and there happens to be important molecules whose energy transition matches your source (a big if), you're going to get a lot of ionization.

I should have mentioned a more established issue is fluorescent lamps emit more blue/violet and UV than LEDs (LEDs are usually packaged in plastic anyways, so even if the emitted there'd be no risk of uv exposure). In common molecules the more prevalent ionization energies are UV and beyond, that's why the risk is greater.[3]

[1] https://en.wikipedia.org/wiki/Energy_level

Electron states are central to molecular dynamics and chemistry.

[2] Infinitesimal ideally, just small in reality because of tolerances as mentioned

[3] https://en.wikipedia.org/wiki/Fluorescent_lamps_and_health#U...

https://www.scientificamerican.com/article/can-compact-fluor...

Interesting. Thanks. I had no idea that compact fluorescents let out so much UV.

That's how photosynthesis works, too, only the electrons are free to move in a wider band [http://www.ucmp.berkeley.edu/glossary/gloss3/pigments.html]. But there's more to the whole process, other molecules and what not.

Plants are known to have been "burned" by LED, and not due to heat. Some turn pale if they don't get a broad spectrum, if I remember correctly.

> No, the diodes don't, the drivers do. You are speaking to a technical audience ;)

I've seen 'drivers' that are nothing more than a resistor in series with the LED. So the LED, acting as a half-wave rectifier, causes the flicker. To your point, in this case the LED should be considered part of the driver.

No, the LED itself literally flickers. Now, that may be because of a shitty driver design... but it’s not wrong.

Thanks for the corrections, yep I was a bit sloppy. But I hope the main point came trough - which is that you should choose carefully when buying LED bulbs, lots of crappy ones on the market.

> No, the diodes don't, the drivers do. You are speaking to a technical audience ;)

Pulse width modulation. ;)

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