Lighting level at opticians

We know lighting quality has a large effect on the ability to read a Snellen chart.

Opticians use no natural light, but is there some standard of illumination level for an optometrists room?

I found the following searching the internet. Don’t know if it’s typical.


Anecdotal but I’d venture a guess and say there are no real standards.

Maybe there are. Though the hundreds of optometrist offices I’ve been in have ranged in every possible creative way in how they measure. From well lit room and white walls and nice printed charts, to charts projected onto a wall in what looked like an old closet, to charts stuck to the back of a cabinet, and everything in-between.

I’m sure if we asked in the Facebook group and caught some of the optometrists that lurk about sometimes, we’d be told different (and maybe more accurately, with possibly some things they’re meant to be doing or are common in specific areas of the world).

Technically, yes there is a standard used for licensing and certification. That doesn’t mean that the standard is being followed by optometrists in the field since it isn’t enforced for clinical measurements.

That said, according to international ophthalmic standards (aka ISO 8596:2017), the luminance or brightness should be between 80-320 lux uniformly across the exam room during a proper visual acuity exam. This includes the eye chart and the room itself.

As a point of comparison, 350-375 lux is equivalent to a 25-watt incandescent bulb at full brightness. So yeah, that is pretty darn dim.


Any idea why the standard is so dim? Do they want to make sure that you can see 20/20 in the dark?

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OMG :scream:
tagging @Humble and @Kevin.L
I’ll throw away my LUX-meter. I’ll just try reading my Snellen in an almost pitch black room to practice for the next opto appointment, and I’ll limit the outdoor time to night and the forest

@Merlin93 thanks for searching for this info, even if the finding is appalling.
But then how does this opto standard match with the “guide for recommended light level in different workspaces” that one would like to believe is integrated in a few H&S standards?!?


Actually, you’re not far off.

At the end of the manifest refraction, the goal is that you should have a prescription that will allow you to see at your maximum visual acuity when driving at night or when working in dim conditions. So most people will end up overcorrected by around 0.50 (± 0.25) diopters over what you’d need to hit your max visual acuity during the day.

This is done both for liability reasons (they don’t want people getting into accidents and then suing their opto because the eyeglass prescription didn’t allow them to see properly at night) and for performance reasons (people will complain if they don’t have the best acuity when doing things around the house at night, etc.)


Ahhh yes that makes sense. In that case I’m surprised there aren’t more optometrists selling separate daytime and nighttime glasses. I suppose being over-prescribed isn’t considered an issue by them, at least I’ve never heard an optometrist express concern about this.

Actually, I didn’t need to look it up since this is something I had picked up a while back. I just needed to check my notes for the specific ISO standard. :slight_smile: I am actually rather well versed in a lot of optometric practice and techniques having been researching it for the last year or so prior to learning about Endmyopia. At one time I was considering going into the field myself.

It doesn’t. The goal in the clinic is to get you to a visual acuity that you can work properly in dim lighting conditions. You will always be able to see better in brighter conditions, so they target for the worst case.


Being overprescribed is something they try to avoid… to a point. There are tests (duochrome test, 0.5 check, etc) that are supposed to be done at the end of a manifest refraction that are intended to identify if you’ve been overminused. Many opto’s don’t do this since it adds another minute or two in the chair and cuts into their profits. But the good ones (and most fresh grads) will always do so. However, that is again done with the low-light conditions so you’ll always be overcorrected in daylight.

You can ask for your refraction to be done in brighter conditions, or specifically ask to be slightly undercorrected, but you may need to have a good excuse to get them to go along with it. Like “full nighttime correction gives me headaches, and this is what my last opto was doing”, etc. Though you may need to say you don’t drive (or don’t drive at night) or something for liability purposes.

I’m sure they wouldn’t mind selling you a “daytime” and “nighttime” pair of glasses though if you were to ask for it. :slight_smile:


Thank you @BiancaK for the tag. Excellent conversation. @Merlin93 has added some great information, so Thank you as well.

I used to believe optometrists over prescribed to give that super HD, ants from space view, unnecessarily. I’ve been recently thinking more as Darrin describes above. I’ve discovered I need .25 diopter over my bright light 20/20 lenses to get close to 20/20 in low light, maybe under 80Lux. I now feel I understand the low light exam room practice.

I still think many of us were over prescribed for years, but now I don’t feel as bad about it. My current understanding is distance lenses for close work is our biggest problem, and a slight over correction is a much smaller factor.

Now cylinder correction is another matter entirely. I blame my astigmatism on poor optometrist practices.


Obviously lumens (lm) and not lux (lx).

350 lux (lx) is like a decent office lighting, according to Wikipedia.

80 lumens or 6W incandescent is pretty nothing - it could match only backup garage lighting.
So the only way the standard talks about luxes and not lumens, thus the standard says it should be comparable to lighting at living room and up to office one.


Lux is what matters. Light intensity at the surface is useful information.

Lumens and watts are misleading and are better left out of this discussion. Watts is electrical power consumed and lumens is total visible light emitted. Neither tell you how well anything is illuminated.

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Lumens represents the total output of visible light from a light source (measured as the output, not the illumination). One lux is equal to one lumen per square meter (lux = lumens/m^2) which means how well it illuminates an area.

The standard I mentioned above is in lux since it is talking about the area of brightness not the output of the individual bulbs.

In general, Wikipedia isn’t a trustworthy source of reference information, but in this case it doesn’t seem too far off. According to my light meter, 320 lux is about the same as the shady part of my office during the day. So dim, but not dark. I could see that being used as general illumination in an office, but not for task lighting, which is generally going to be more like 500-1000 lux. Though keep in mind that the reference range is 80-320, so darker is more likely.

I don’t know if it is accurate since I don’t have any 25W bulbs to test, but when I did a conversion from 320 lux to incandescent equivalent, the 25W bulb was the closest I could find, listed as providing 350-375 lumen. This is why I used that as a point of comparison.

Heard of these unicorns, never personally experienced that exam. :grimacing: (obviously very anecdotal and nothing more than another manifestation of my disgruntled-ness at the default state of affairs)

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Yeah, unfortunately there are no requirements for clinical refraction techniques, so a lot of the more experienced opto’s seem to streamline the process in my experience. In fact the only time I’ve gotten a proper full refraction was when I was getting fitted for contacts a few years back and that was with a relatively new optometrist who’d only been practicing for two years since ending her internship.

From everything I’ve learned, optometrists and ophthalmologists are taught the best practices which include doing a second MPMVA step and testing for overminus at the end of the session. Heck, within their own journals and magazines they talk about being careful not to overminus patients (likely because they know that minus causes hyperopic defocus and leads to faster axial length increases) but not everyone does so. I don’t know if it is overconfidence in their own refractive ability, laziness, or just a desire to get folks out of the chair faster so they can hand them over to an optician.


depends on the opto but yes that’s why I stick to the good behavioral optometrists. My current one has a sign at the front desk of his clinic saying he prescribes different lenses for different situations, like computer use, driving, sports, etc. He still does his refractions in a dim room with the curtains closed but uses different standards for different glasses types, like I think 20/40 for normalized, 20/20 for driving and uses a projected snellen.


Common Light Levels Outdoors from Natural Sources Common light levels outdoor at day and night can be found in the table below:

The table below is a guide for recommended light level in different workspaces: