Visual Display of Brightness (Lux)

A discussion on Brightness values (Lux) and how to interpret the values to display a named vales and image.

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solar wm/2 is approx equal to 0.0079 * Lux value

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The relationship between Solar radiation and Lux is not linear.

"It is not possible to take the luminous flux and obtain the insolation (as radiant flux). Here’s why:

The luminous flux F is calculated from the radiant spectral power distribution J(λ) by weighting each wavelength with a luminosity function y(λ) as per


where c is some unit conversion constant between lumen and watts. The total radiant flux Φ would be


The problem is that the calculation of the luminous flux is not invertible - portions of J(λ) lying outside the visible range are cut off by the luminosity function being zero there, and it is perfectly possible for two J(λ) of different radiant flux Φ to have a similar luminous flux F."


Here it is.


Can you offer what that value will look like in a chart / graph?

Brightness, UV, and solar radiation:


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You can see for yourself, right here:

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Go to the map:

Pick any of the stations at this location:


Thank you all for sharing . . .

I understood the development team was pondering how best to render the brightness values. When I see Hanksters charts the value(s) of 100,000 either comes across as wow.

That’s a huge value but what does that mean to Human?!? :thinking:

This is why I suggested to the development team to provide imperial value like what Hankster has offered here. Along with something a person can relate too such as a light to dark phrase and color strip.

Sorry can’t load a picture here so use your imagination and the values I use are just random:

0.00 Lux / what ever 50 Lux 100 Lux 100,000
<----- ------->
Dark Light Moderate Extreme
Black Yellow Orange Red

Anyways this is why I asked about the brightness sensor because I wanted to help our other team come up with a method to best render those values that made sense to Human. :sunglasses::heart_eyes:

Maybe this will help.


And this should help:

The end result is that what you are asking is already documented.

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The chart you provided is helpful only if its present for the end user. This is why my inquiry was about how best to relay numeric values to Human. Nobody is going to know 10, 752.7 is daylight vs 107,527 is sunlight or any other value in between.

As noted early on my primary goal is to help a couple of third party developers come up with a visual method that includes numeric, words, and color scale. My primary focus in all of the Alpha / Beta programs I have been involved in has been to help make a product, service, human ergonomically simple, easy, for the lay person.

The goal is to have a At a glance view where anyone seeing X vs Y knows with out thinking for example 107,527 = Sunlight = Red color strip etc. Any other value would fall within the gradient so again a person at a glance could identify a numeric value and translate it to human readable.



As you are wanting to provide this data to a developer, a developer will know. That’s how I know. So simply pass the data on to them. Better yet, have them join the forum here and get first hand help.

That’s the data I am using for RTI and ISY drivers.

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Kind of hard to explain. Lux is not a measurement of how bright a light source is but lux will be how bright the surface illuminated is going to be. Does this help?

Full moonlight = ~1 Lux
Dark overcast day = 100 Lux
Office lighting = 300~500 Lux
Halogen Headlights @25’ = 500~550 Lux
Direct sunlight = 32000~130000 Lux

It may be a concept that many people will not be able to grasp.


Appreciate the feedback and insight but as stated my belief and goal(s) are to make the numeric values meaningful to all where at a glance it makes sense. Everyone knows by looking at a image of a half moon that it directly translates to: (half moon = 50%)

A full moon equates to 100% etc.

Anyone can indicate a value but if it has no human reference its meaningless to the public at large. Weather34 (Brians) PHP web page is the perfect example of simplicity and common sense. A ten year old child knows at a glance viewing a cylinder the amount of liquid equals X volume / Y height for a given defined vessel.

The same way Brian has rendered how the wind direction equates to its numeric value by providing a simple circle with phrase, numeric value, symbol, etc.

My expectation is to see the very same for brightness . . .


Since they are yours, you have the choice of using standard formulas or inventing your own. You can use the above graphs and information to create the images you want to display.

As for Brian, he is using standardized formulas and calculations. He can do the same with brightness.

@Weather34 Brian, what are your thoughts on a visual indicator? I am considering an indexed heatmap type vertical bar.

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hello i have done something a few weeks back however my newer sky unit is stuck in customs here in istanbul. so here is how I was going to use the Lux data ive not done anymore and will polish it off once i have the newer unit installed but it will look like this . still need to work on descriptive text in relation to the value at different times and fully test it for a few days on a live not sure i will use the Lux value on the main page just include it in the pop up module… im going for the simple output heatmaps will confuse anyone outside the enthusiast area .

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hi patrick

think you know i worked at a school and used that experience of how to interpret certain things visually and make it understandable. colors were a strong feature of teaching younger students it got them over the 1st stage of understanding unfamiliar or new subjects etc… weather data doesnt have to be complicated however i tend think a specific user wants more than the daily relevant weather data they will find a way of implementing it.if you implement every possible idea ive had requested over the last few years unlikely it would look like it does currently .

a year or so ago i got 5 grade 7 students together and simply asked some basic questions like what is the temperature, whats the wind direction, so on using the template all came back with answers within seconds… none had seen or had remote interest in weather apart from is it going to snow sir :grin:…so they get a day off…

my goal is to install a weatherflow air and sky at the school in the near future…the teacher i was working with on it and we purchased and had planned last year to install a davis but he left and went to china and his replacement is not ready still learning the ways of the school so hopefully next year term it will happen.



IMHO, a LUX number is pretty much meaningless for anyone other those in the photography or lighting field. It is almost never used for weather related data. Who is going to explain to the “masses” that if you place a 100 lumen bulb in a flood light that shines on only one square meter of surface, that surface will be lit at 100 lx. However, if you back the flood light away to shine on four square meters, the surface is now lit with 25 lx. And that relates you and weather how?

When was the last time you have ever heard any weather related information that contained the word “LUX” in it? Now if you are a photographer, lighting engineer, stage hand, commercial building designer you will have used LUX in your calculations.

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your probably absolutely right but has we have seen other technologies and formulas creep into the hobby .i share the same opinion about web cams and weather especially at night 90% of them have or displaying a dark non viewable scene or sky. however we all have different interests , where would i use lux ? no idea yet… time will tell if I find any personal use off it …i have a couple uni students i help out im sure they will hink of something nearby ambient light or something …really dont know personally…brian

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