Hacker News Reader

Comment by _3yjt | Hacker News Reader

IEEE Recommended Practices for Modulating Current in High-Brightness LEDs for Mitigating Health Risks to Viewers : https://standards.ieee.org/ieee/1789/4479/

There is nothing anecdote about flickering in LED light causing health risks.

View on HN

I am not questioning that certain types of flickering are harmful, so that there's an IEEE standard for how to safely use PWM does not contradict what I said.

What I'm asking for is for articles like this that cite numbers and provide tables purporting to quantify the degree of harm caused by various devices to point to where they're getting their numbers from or, if they can't do that, stop making up numbers and assigning things to "harm" scales that they invented themselves based on vibes.

Either there's a study showing that 246 Hz flickering poses "Extremely High" health risks or there isn't.

See my comment on the other reply.

> Either there's a study showing that 246 Hz flickering poses "Extremely High" health risks or there isn't.

They calculated it using the definition from the standard.

Can you please cite the page number where this definition exists? When I search for "extreme" in the standard that the other commenter links to I don't turn anything up, so I'm unclear where that classification is defined.

31 and 32 (by the printed page number), in pdf it’s 42

The article contradicts the IEEE paper.

They list the 'Xiaomi 15 Ultra' as having a 'Moderately High' health risk, and cite it as having a 2.16 kHz PWM frequency at 30-75% modulation depth.

The IEEE article has recommended practices that state:

8.1.2.3 Example 3: PWM dimming Using Figure 20, the recommended practice for PWM dimming at 100% modulation depth is that the frequency satisfies f > 1.25 kHz. This can also be derived using Recommended Practice 1 and solving 100% = 0.08×fFlicker. This level of flicker could help minimize the visual distractions such as the phantom array effects.

Seems like even at 100% mod depth, >1.25 kHz is just fine.

Also, the article does not seem to distinguish between modulation at reduced brightness, which the IEEE article calls out specifically as something that is unlikely to cause issues. E.g., movie theaters using film all flicker at 48 Hz and nobody complains about that.

That does not define the scale that they're using. That's a typical hazard analysis risk matrix which has two axes which can be converted into a 4-point scale (Low, Medium, Serious, High). Importantly, to do a risk assessment in the style of IEEE 1789's you have to identify the specific Hazards that you're analyzing, which TFA does not claim to be doing in that table, instead speaking vaguely of "health risks". IEEE 1789 does not provide a mechanism for evaluating "health risks" without specifying exactly which risks are being evaluated.

You can see on page 27 how this is meant to be used: it should produce a per-hazard matrix.

You might be thinking of Figure 18 on page 29, which does identify Low-risk and No-effect regions by Modulation % and Frequency, but that also does not claim to identify high-risk regions, it just identifies the regions we can be highly confident are safe. And importantly, as a sibling comment notes, TFA's table actually contradicts the line on Figure 18, labeling several devices as higher than Low even when they're squarely within the Low-Risk and No-Effect zones.

Was it an astronomically high health risk to watch a TV set that flickers at 60 Hz or movies that flicker at 48 or 72 Hz? (It is 24 frames per second but you'd perceive a lot of flicker at that rate so the shutter has 2 or 3 blades)

Here is a non-paywalled link: https://www.lisungroup.com/wp-content/uploads/2020/02/IEEE-2...

Sure, PWM light can cause health risks for some people, in some contexts. But taking research out of context is bad science.

Do you genuinely believe the Pixel 7 and 8 Pro have an "extremely high health risk", in the context of what a lay person would understand?

Edit: I specify 'lay-person' because clearly this is an introductory blog post (or advertisement for Daylight Computer). If they want to use a more specific definition of health risk, then they better define it.

The “very/moderate high” comes from the standard itself, which is quantified within the standard. In the context, it is about the probability of having issues, while the effect (mild to catastrophic) is another axis. Considering that they stick to the “official” wording and seeing the criticism, I am not even sure if they can change to a more “lay-person” friendly and be acceptable to all the critics.

The standard also linked to the researches during their discussion.

Please read it, instead of just randomly throw out things hoping that they supported your argument.

You can't just point people at a 60-page paywalled standard and say "the supporting evidence to my claim is somewhere in here, I pinky promise". You are the one making assertions, it's on you to prove that the standard actually does reflect the text of TFA. I'm not going to read the whole standard because I'm not the one making the argument and I can't be bothered doing the research needed to refute every piece of nonsense science that shows up on the internet. What I can do is point out when someone is making unsourced claims and insist that they provide their sources if they want to be taken seriously.

Cite the exact page number and quote that you claim justifies the assertion that 246 Hz PWM carries an "extremely high" health risk. Then we can talk.

Look, they sourced their claims (quite literally, they put how they calculate, from which standard). And linking to the correct document is literally how scientific citation works — I replied the page to you above anyway.

If you want to redo the numbers and check if they fit the definition, please feel free to do so, but you will need to put some works in (since the flicker hz -> risk showing in the article is a computed value, you need to find the modulation value and plug it in too)

I understand your fight and your idea, I am just saying that in this specific instance, this is not a fight to be fought. The article is generally correct, and if you want to complain about the writing style or it being an ads, it’s up to you. But this is not the same situation with GMO stuffs

> Look, they sourced their claims (quite literally, they put how they calculate, from which standard).

No, they said that IEEE 1789 also uses Modulation % (which they've renamed Flicker %) to calculate risks. That is pointedly not the same thing as claiming that they used IEEE 1789's formulas.

You're reading their copy generously, but that doesn't usually pay with marketing copy. Articles like this always like to wave in the general direction of official-sounding sources while carefully refraining from actually claiming that they got their numbers from anywhere in particular.

Reply on news.ycombinator.com