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u/Typical-Sample5301

r/LibraryScience r/Lighting
Image 1 — spent a week measuring lux in 3 public libraries — the "brightest" reading room had the worst eye fatigue scores. here's what i found
Image 2 — spent a week measuring lux in 3 public libraries — the "brightest" reading room had the worst eye fatigue scores. here's what i found
▲ 19 r/LibraryScience+1 crossposts

spent a week measuring lux in 3 public libraries — the "brightest" reading room had the worst eye fatigue scores. here's what i found

ok so this is gonna sound dumb but i actually did this.

my kid kept complaining her eyes hurt after 2 hours at our local library, so i borrowed a cheap lux meter off a friend (he does theater lighting) and just... started measuring stuff. three libraries near me, same week, all on cloudy days so daylight didn't mess things up too much.

what i expected: brighter = better for reading. what i got was the opposite.

library A — newest one, all recessed downlights, ceiling looked like a runway. measured 750 lux at the table. felt like a hospital. my kid lasted 40 minutes before rubbing her eyes.

library B — older building, those old fluorescent troffers half of them flickering. 380 lux. obviously not great either, gave me a slight headache after an hour.

library C — this one surprised me. mix of indirect uplight bouncing off a white ceiling + small task lamps on each desk. only about 450 lux at the table but the WHOLE room felt evenly lit. no shadow on the page from your own head. my kid did almost 2.5 hours without complaining once.





what i think was going on (happy to be corrected):

- it's not the lux number, it's the ratio between your page and the wall behind it. library A had a bright page and a dim ceiling above it — your pupils don't know what to do.
- glare off glossy book pages was way worse in library A because the downlights were basically point sources right above the table.
- the task lamp + ambient combo in library C meant the contrast between "looking at book" and "looking up at the room" was tiny. less pupil work = less fatigue.
- nobody talks about ceiling brightness but i think it matters more than table lux for long reading sessions.

stuff i didn't measure but probably matters: color temperature (A was super cold, C felt warmer, maybe 3500K?), flicker, and CRI for looking at illustrations/art books.

am i totally off base here? anyone who actually designs library lighting — is this the "luminance ratio" thing i've half-read about, or am i inventing patterns? and is there a sweet spot lux number people actually aim for in reading rooms, or is it always "it depends"?
u/Typical-Sample5301 — 13 days ago
▲ 3 r/Lighting

measured glare and flicker in 9 hospital wards last quarter — the new "premium tunable-white" retrofits were the worst offenders

so i've been doing post-occupancy walkthroughs for a regional health network after nurses kept complaining about headaches on night shift. management swore the new lighting was "the best money could buy" — tunable white, dali-2, the whole package. went in expecting the old t8 wings to be the problem.

ran an opple light master and a cheap konica minolta loaner across 9 wards in 3 buildings. expected the 15-year-old t8 corridors to flunk. they kinda did. but the surprise was the newly retrofitted wards.

a few things that genuinely caught me off guard:

- UGR at the patient's pillow (looking up at the ceiling) was creeping past 22 in 6 out of 9 rooms with the new panels. on paper the fixtures spec UGR<19, but that's at the standard observer position, not lying down. nobody designs for the supine view.
- flicker (PstLM) on the "premium" tunable-white drivers was 1.2–1.6 at the dimmed warm setting nurses use at night. the old t8s with magnetic ballasts were ~0.4. dimming the new stuff actually made it worse.
- CRI was labeled 90+ but R9 measured 18–35 in two exam rooms. skin tones looked grey-green. one doctor said she'd stopped trusting her own visual triage and just ordered more bloodwork. n=1 anecdote but it stuck with me.
- the dali-2 system was installed but never commissioned for a circadian curve. it's basically an expensive on/off switch. nobody on the facilities team knew what casambi or a scene controller did.

so the "premium retrofit" was measurably worse for patients and staff than the 15-year-old fluorescents it replaced, at least on glare and flicker. cost ~6x more. could be a commissioning failure more than a fixture failure, hard to say with n=9.

a few questions for anyone who's done healthcare audits:

1. do you measure UGR from the patient supine position, or stick to the EN 12464 standard observer? feels like the standard misses the actual use case.
2. has anyone seen tunable-white drivers that hold PstLM <1.0 across the full dim range? every spec sheet i've seen only quotes 100% output.
3. is R9 ≥ 90 actually enforceable on a hospital tender, or do we just write it and hope?

happy to share the measurement spreadsheet if it's useful, just dm.
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u/Typical-Sample5301 — 1 month ago
▲ 18 r/Lighting

Measured flicker in 14 classrooms last month — the "premium" LED panels were the worst offenders

so i've been doing lighting audits for a school district that had complaints about kids getting headaches and trouble focusing after lunch. district had retrofitted everything to LED 3 years ago, top-spec panels, the whole deal.

brought a flicker meter (just an opple light master, nothing fancy) to 14 rooms across 3 buildings. expected the cheap stuff to fail. it did. but the "premium" 0-10v dimmable panels were actually worse at 40-60% dim — Pst LM creeping past 1.5, SVM around 0.6.

a few things that surprised me:

  • the panels themselves were fine at 100%. the problem was the dimming driver. nobody specced flicker performance, just lumens and CCT
  • the rooms with the worst readings were also the rooms teachers had flagged informally. not a coincidence
  • swapping one room to fixtures with PstLM <1.0 across the full dim range — teacher said within a week the afternoon "zombie hour" was noticeably better. n=1, anecdotal, but still

questions for the sub:

  1. anyone else seeing this gap between datasheet flicker numbers and actual in-situ measurements?
  2. is EN 12464-1's PstLM <1.0 actually strict enough for k-12? feels like it should be stricter for kids under 12
  3. what's your go-to spec language to force manufacturers to publish flicker at multiple dim levels, not just 100%?

happy to share the raw data if useful, just don't want to dox the district

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u/Typical-Sample5301 — 1 month ago