My workstation environment - lighting

[Rufus]

I am looking to refine my editing environment now that I have redecorated it.

I have pale to mid grey walls, a white ceiling and several white cupboard doors behind me. The window is fairly small (about 1 square metre / 1 square yard) with a grey blackout vertical blind so I can reduce the amount of daylight significantly. It potentially allows daytime and night time light levels to be similar.

There is a ceiling light fitting with 3 spotlights that do not point toward the screen but can provide some general illumination. The bulbs are a tad on the blue side but are the best I could find: 6500K, 575 lumens, CRI 90, dimmable, made by Phillips.

I am about to recalibrate my BenQ monitor for its new surroundings. I realise that the brightness of the environment will affect my perception of the displayed image and can lead to a mismatch between the on-screen image and the printed result.

I also recall Manfred saying his environment has about 70 lux and others a bit higher. I cannot find any tips on how to measure the lux value in the absence of an incident lightmeter. Can a sheet of white paper and a camera’s (reflective) lightmeter be used to arrive at a suitable brightness?

In the UK a lightmeter (Sekonic L-208 Twinmate) costs about GBP125 (USD150) which I am reluctant to spend as it would have no other value for me.

I have a feeling this has been touched on before but my searches have not come up with anything. If I am overthinking this feel free to tell me.

[DanK]

I bought an old, used Sekonic incident meter an eBay solely for that purpose. I think it cost me about US$20. However, I just looked, and the prices seem to vary from $10 to $400!

I'd characterize the level I ended up with as "moderately dim".

I don't know how to do this with the camera's meter. I'd be very interested if someone can show the math.

Re lights: CRI is only part of the issue. That metric omits key reds, and many LEDs that are sold without R9 values have weak red production. I don't know what's available in the UK, but in the US, if you search long enough, you can find bulbs that have published R9 values over 90. There is also an Rf (fidelity) index and an Rg (saturation) index, but those are are rarely made available.

The bulbs I use where I edit and proof photos are Soraa Vivid BR 30, 3000K. The values are CRI=95, R9=95, Rf=90, Rg=100. They run close to US$20 each. I can't say whether it's made a difference in how I printed, but it makes a substantial difference in how the prints look, particularly the reds.

[Manfred M]

The range for the screen should be 80 - 120 candela / square meter. Because I do a lot of printing, the lower end of the range (80) makes my prints matchup to the brightness of what I see on the screen quite well. You need to shield your screen from the direct light of your lights.

Rather than buying an incident light meter, you might be able to find a phone app that does a reasonably good job for you. The general recommendation is that the light at the work area needs to be below 70 lux and ideally below 30 lux. At that light level you should be able to read a book for short periods, but will find it eye straining.

The CRI 90 is not good enough to evaluate your prints under. A good rule of thumb is to evaluate the prints under the light that they will be shown under, but that is not always easy or possible. I have been told that a good compromise is to evaluate prints with 150 lux of light on them.

Just remember, your screen, with its transmitted light, additive process,RGB output will never match your printed output which uses reflected light, subtractive process and a CMYK process. Close is as good as it gets.

[Rufus]

Thank you Dan and Manfred for your thoughts.

I have recalibrated based on 80 lux which I believe is equivalent to 80 candela per square metre.

I knew my lightbulbs for ambient light would fall short of the ideal, but I searched in vain for normal UK mains lightbulbs that were any better. I shall see how I get on with these.

As I have not found a club to join since moving home any prints will be for my domestic enjoyment and therefore I can test the prints in the ambient light that they will be in.

I had not thought that a phone app might be available that measures incident light. An initial search found exposure meters that indicate a shutter speed and aperture for a given ISO but they don't show the lux value of incident light. I will take a more determined look for one.

This evening I printed a 4x6 image and compared it to the screen and it seems similar enough to me. Tomorrow I shall use the low light reading test and see how I get on.

[Stagecoach]

I had not thought that a phone app might be available that measures incident light. An initial search found exposure meters that indicate a shutter speed and aperture for a given ISO but they don't show the lux value of incident light. I will take a more determined look for one.

I have just downloaded the free 'Lux Light Meter Pro' App from Google for my phone which gives the Lux value.

Very clear basic readout of Lux or Fc values, a good help page that explains how it works and lists suggested values of common spaces and outdoor conditions.

[Rufus]

Thank you for the lead Grahame. I have looked into the Lux Meter Pro in the Apple App store. That led me to the Light Meter LM-3000 app which can be tested for free for a limited number of times after which its "battery" runs out and a lifetime "battery" can be purchased for GBP6.99 in order to use the app for ever (or more correctly until the OS is no longer compatible!).

The LM-3000 is simple to use and the one off charge seems reasonable. I shall never know how accurate or otherwise its readings are but it will enable me to check the light levels at different times of the day and evening while I get used a light level shown as 30 lux.

[Manfred M]

A couple of light measurement distinctions:

candela / square meter (a.k.a nits) is a measurement of light emssion at the source. This measurement is taken by placing the meter against the source.

lux is a measurement take at the work surface (i.e. the light falling on it) and the value will be different at different distances from the light source (a practical example of the inverse square law at work).

The two terms are not interchangeable and measure different aspects of light.

This chart helps convert a light meter reading in ev to lux.

[Rufus]

A couple of light measurement distinctions:

candela / square meter (a.k.a nits) is a measurement of light emission at the source. This measurement is taken by placing the meter against the source.

lux is a measurement taken at the work surface (i.e. the light falling on it) and the value will be different at different distances from the light source (a practical example of the inverse square law at work).

The two terms are not interchangeable and measure different aspects of light.

You also said in post #3 “The range for the screen should be 80 - 120 candela / square meter.” So I set the Luminance in Calibrite’s Palette Master Elements software at 80 on the assumption that it corresponds to 80 Candela / square metre (but this may be an invalid assumption).

And in the same post “The general recommendation is that the light at the work area needs to be below 70 lux and ideally below 30 lux.” I have established from the phone App how much ambient light produces a reading of 30 lux when the phone is on the desk in front of the display screen. I hope thereby to have an appropriate ambient light by adjusting the blind or electric light dimmer to reach that reading.

So far the prints look reasonable compared to the screen although the colour saturation of a cloudy blue sky is liitle reduced so far as the blues are concerned. To check this I shall need to test some other images.

[Manfred M]

I have recalibrated based on 80 lux which I believe is equivalent to 80 candela per square metre.

I was referring to this line. in my response in #7. Lux and cd/meter squared are two completely different measures. Sort of trying to compare pounds and gallons.