Reading lamp 2

[prc]

I believe eng-tips do not have an illumination engineering forum, so I am posting this query here.

What is the best lamp (eg LED) for the reading desk? What is the optimum lumen for comfortable reading?

 

[itsmoked]

That's a tall order because it depends on the individual and exactly what they're doing at the desk. I bought three and took all of them back.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[TugboatEng]

I wouldn't consider lumens first. Strobing is the #1 concern for LED lights and eye fatigue. Well filtered power/light is a must.

Next is the color temp. I know for working near daylight is best as it reveals the most detail. Personally, I feel that a color temp around 3500k is most comfortable for starting at something.

 

[dik]

Tug's got it... I prefer 3500 to 4000 for working... current work space uses 4000. Anything lower is hard on the eyes and anything higher is carrying a little more blue with the bright light than I like. I was not aware of strobing, I've not noticed it, but with the 'speed' of LEDS, it might be a problem with 60 cycles... likely a problem if you have 50 hertz power.

So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[3DDave]

It's not the lumens from the bulb but the lumens on the page that matter. A light meter is required, but by then the person can decide if it is bright enough or not.

There are reports that too much blue can make it tougher to soon fall asleep, so if the reading is within an hour before bedtime then a lower color temperature is better.

It's also the case that "white" is made by slapping a phosphor mixture on top of a UV LED, so there can be UV bleed, but also a discontinuous spectrum.

Recent experience: I put some LEDs into the interior car lamp holders and while it looks "bright" it simultaneously seems "dark" The last time I came across that was with mercury bulbs that also use phosphors - a look at them with a diffraction grating showed only a couple of narrow bands with most of the spectrum missing, leading to anything with color in those bands having no light to reflect.

 

[jraef]

I worked for a short time on industrial lighting and so received specific training on this issue.

There have been studies on the “best” light for reading, showing that a CCT (Corrected Color Temperature) leaning toward the blue is best for reading speed and accuracy as it causes the pupils to narrow and allows focusing on entire words rather than individual letters. But the main study (I’ll find a reference for you later) found their own flaw in that the data was gained inconsistency as the age of the participants increased (above age 49), so the one I read some time ago said they were going to delve further into that and since I was more interested in industrial task lighting I never looked for the follow up study. But aside from the CCT, the way the fixture delivers light to the reading surface, as measured in lux, is more important that the lumen production of the lamp. Lumens are measured in a sphere with the lamp in the center, lux is a measurement of lumens on a surface and in the case of reading, the page. You want around 850 lux to reach the page. Also important are the contrast between the type and medium and the size of font (6-12 was best by the way). In other words lumenocity and color temperature of the lamp alone are not the only consideration.

The issue with blue spectrum shifting is that more modern studies have now revealed that blue light affects melatonin production, which is why it has been linked to disruption of circadian rhythms (sleep problems). Hence the recommendation of not reading computer, phone and tablet screens right before going to bed. It IS better for the reading aspect, but not for the sleeping part.


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

 

[EdStainless]

Most inexpensive LED power supplies strobe, the better ones have smoothing capacitors in them to minimize it.
How much it takes to bother you is another issues.
Fluorescents do the same thing.
You will also see lamps with a CRI (color rendering index), nobody mentions it unless they are 90 or higher.
To get good CRI you have to use a mixture of wavelengths (multiple phosphors) which cots more.
These are some of my favorite lamps, either in 3000K or 4000K.

https://www.waveformlighting.com/human-centric

I use some of their other products as well.
I have some of the LED strips along the edges of my monitor that I use to illuminate my face during video calls.
And I have put their LED tubes into overhead fixtures.
If you are doing photo work and color matching then you want 5000K and >95CRI, but this can get tiring.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[prc]

Thank you all.

 

[dik]

Neat site, Ed...

So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[Amit Bajpayee]

According to me no one-size-fits-all answer to this question, as the best lamp (eg LED) for the reading desk will vary depending on your specific needs and preferences. However, a good rule of thumb would be to choose a lamp with a high lumen rating – this will ensure that you are able to read comfortably in low light conditions. Optimum lumen ratings can also depend on how often you plan on using the lamps for reading purposes – if you primarily use them at night when it's dark outside, then an illuminated lamp may be more desirable than one that is off completely during the day.

https://agnisolar.com/

 

[sunnysky]

The best light intensity depends on the background light intensity as the eye pupils adjust to the field of view.
So there is no fixed optimum intensity is just enough to minimize eye strain from being too dark or too bright.

My estimate is that the contrast ratio or SNR of reflectance for good acuity ought to be around 20:1 and slightly brighter than the surroundings.