Matching north light with fluorescent bulbs
 

I am in the process of reevaluating my studio lights. I have been using 4 foot T-12 bulbs by Ott. The color temperature is 5000 degrees Kelvin and the CRI (color rendering index) is 91. The Color Rendering Index determines how accuratly color can be seen.

I feel the light is too warm and doesn

Marvin, I unfortuntely do not know the specifcs with regard to CRI, although from what I have read is it extremely important.

There is enormous variability in the range of Kelvin temperatures, even controlling for the time of day. Temperatures are dramatically affected by atmospheric conditions, humidity, and altitude. Research I have done with respect to general Kelvin temperatures indicates generally that the light at noon is about 6500 degrees K, in sunlight.

North light conditions that would be as you are describing, would be light uninfluenced by direct sunlight. At noon the temperature could well exceed 15,000 degrees K, but that would be more characteristic of somewhere like Taos, with low humidity, high altitude and cloudless skies. In New York City, I would have to presume the temperature is much lower...salt air, lots of humidity, pollution...all things that influence the temperature of light.

If my memory serves me correctly, it is possible to measure Kelvin temperature for a specific geographic area (of course it would need to include assumtions about the atmospheric conditions), if you indeed want to pursue lighting that would mimic what you would normally have, given the location of your studio. This would be practical if you found yourself combining natural daylight and studio light. If I can recall how you might go about measuring specific Kelvin temperatures, I'll post it...it's been a while.

I am not aware of any manufactured bulbs that are rated at high K temperatures, but there certainly may be some. As I only paint in nautral daylight, I haven't had reason to look. Of the three bulbs you mentioned, I'd presume the higher rated temperature would be preferable to the 5000 K bulbs...it may not, however be enough a difference to appreciably impact choices you might make in your paintings.

Marvin I use GE Chroma 50 bulbs with a white frosted diffuser on the fluorescent fixture which are mounted directly over my window.

This window is not facing directly north it is kind of north east so in the early morning the light is slightly different but It is usually not a problem after 8 am.

I like the Chroma 50s they match the natural light color very well with the white diffuser on the fixture. (The diffuser may have some effect also.)

This is from GE's site about color temp.

Color Temperature

Originally, a term used to describe the "whiteness" of incandescent lamp light. Color temperature is directly related to the physical temperature of the filament in incandescent lamps so the Kelvin (absolute) temperature scale is used to describe color temperature. For discharge lamps where no hot filament is involved, the term "correlated color temperature" is used to indicate that the light appears "as if" the discharge is operating at a given color temperature. Chromaticity is expressed either in Kelvins (K) or as "x" and "y" coordinates on the CIE standard Chromaticity Diagram. Although it may not seem sensible, a higher temperature color (K) describes a visually cooler, bluer light source. Typical color temperatures are 2800K (incandescent), 3000K (halogen), 4100K (cool white or SP41 Fluorescent), and 5000K (daylight-simulating fluorescent colors such as Chroma 50 and SPX 50).

Now after reading this you would think that all 5000K bulbs would produce the same color light but they do not. I have tried many different 5000K and 5500 bulbs the Lite-A-Lux included.

In the GE line of so called daylight bulbs alone the Chroma 50 and SPX 50 which are both rated as 5000K bulbs you get two distinctly different colors if you hold a white card under each. The SPX which has a pinkish coating on the bulb produces a warmer light then does the Chroma 50 which has a grayish white color coating on the bulb.

So my advice is try a few and test them. (maybe you can find a lighting center that would let you return them if you did not like it but I would not count on it since these are usually special order at least for the lighting centers around here. Hope this helps.

P.S. This difference may be because florescent tubes have no filament so the color temperature has nothing to do with a actual filament temperature so the rating is some what arbitrary depending on how the manufacturer measures it. This is just a guess I do not know why one bulb has a different light vs. another of the supposedly same rating but they do.

More info on GE bulbs
 

Directly from GE's site: Well, since I have never noticed a big difference in light between the mix of daylight and my Chroma 50 bulbs and when I am painting after dark with the bulbs alone, it may be because I do not get direct skylight through my window - so I am matching a 5000K daylight and not 7500K sky light. Maybe with a higher window the Chroma 75's would work better for you, Marvin, if you have direct north sky light you are trying to match. Good luck.

I also found some more information on the GE site that explains the SPX 50's different color.

The SPX comes in two different colors: a red-enhanced SP30 or SPX30 for flowering and fruiting plants; or blue-enhanced SP50 or SPX50 for vegetative plants. The SP and SPX are plant grow-lights, so although they are rated as daylight bulbs, their color is not as important as the amount of energy for photosynthesis and other plant photoresponses they provide.

So I guess the GE Chroma 50 or Chroma 75s are the bulbs you want for studio lighting - not the SP or SPX bulbs. I hope this clears up the mistake I made in my first post.

Link to GE site http://www.gelighting.com/na/home/index.html

Bright idea
 

Thanks for the info Michael. I'll keep you posted on my search.

Studio lights
 

Marvin,

I am interested in knowing whether you want to use these lights to paint under or to photograph your models, or both? As somebody who is trying to improve the quality of my source photographs, would you recommend using these lights to photograph and light subjects?

Clive,

You might also check some of the threads on lighting the model here: http://forum.portraitartist.com/foru...?s=&forumid=72

Lighten up
 

Clive,

These lights are for the purpose of illuminating the area of my studio where I paint. My north light is obstructed by trees and sometimes I need more light than my windows provide.

When I take my reference photos I use strobe lights. The reason I use these lights is to compensate for the difference between the way film and the human eye perceive reality.

I have previously gone into some detail about this subject in other strings.

I wouldn't recommend using these lights to light the model unless you want a very diffused soft light.

Marvin:

I have a mostly north facing window. While it is not nearly high enough, it serves and I love the natural light.

I have always wondered about temp and CRI and what the values were equivalent to. In other words, I have heard before that a 5000+K bulb better simulated natural sunlight - but sunlight has nothing to do with the light that you get from a north window and I wonder if it is too intense to simulate what you would get from a north window. Do you have any thoughts about this? What is the temp and CRI of the light coming into a typical north window? Unobstructed of course. :)

I have heard a lot of people talk about this and I wonder if they are getting the wrong info about temp because those companies seem to be selling bulbs that simulate sunlight, not the soft, cool reflective light of the sky that comes through a north window.

Dim bulb
 

Actually Sun-a-lite sells the bulbs. They are made in Germany and Sun-a-lite is a dealer. I have ordered these bulbs and will post the results when they arrive.

Comparisons
 

Sounds like none of us are ready to trust those selling to judge how true their product is. The trouble is that we can't easily compare "stereo A" with "stereo B" which is always very informative when comparing other products. Holding a white card up doesn't really do it either.

I wonder if the curve here is lower than we suspect. When you wish to insulate your home once you pass R-value of 38, any improvements are moot and certainly a poor investment. North light in Iceland in April is very different from North light in Madrid in June. I rather think that if we can get from 5500-6000k, even if this involves mixing of bulbs, then that is likely as good and certainly more constant than northern light which we all concede varies.

On a related subject, too much light in a studio is wicked. Photograghers measure "how much" light all the time. Seems we painters should ask this question too.

Bingo!
 

Tim I am happy to report that your theory doesn't apply to light bulb manufacturers. I just received the bulbs I ordered on Friday. The name on the bulbs is Lumichrome made by Lumiram. They are spectacular. In comparison Ott lights are too green and Ott true color are too yellow. They are not precisely the same as true north light but are so close that the difference is negligible, to my eye anyway.

In addition I've never seen any lights that are better.

Here is the description from their site:

Lumichrome

I'm glad for you.
 

I bought some too. I like them. Two things though. Imagine one room lit by 5500k lights and one lit by 6,000k lights. Without seeing the print on the bulbs can you walk from one room to the other and tell one from the other?

Our eyes adjust like digital cameras and declare "okay, this is white etc. What's that feature called on a digital camera where it reads the light source and adjusts? Secondly, and more important, what happens to the work when it's sold? Maybe (at best hope) 4000k halogens or worse if it goes to a museum with really weak light from 30 or 40 feet away. The museums sometimes use good light color but it's often to far away.

I see the light
 

Tim, the fixture I use in my studio uses six bulbs on two separate circuits so I can flip on three of one type of bulbs and then flick them off and flip on the other type.

The difference is very discernable.

I don't worry about the light my paintings are eventually going to hang in. If it harmonizes in my studio and my values hold it will read wherever it hangs. Also, if you paint a painting geared to a particular color temperature of light what guarantee do you have it won't be moved? The old masters painted their pictures in their north studio light, which is one of the primary reasons for my quest to find a better bulb.

However, since I want to insure that my paintings look good on the wall, I recommend a great picture light made by fineartlight.com. They custom design their fixtures for each painting. Another fabulous product and definitely worth every penny.

More lighting questions
 

Hey Marvin,

My concern here is not only my paintings but my health. I was using regular ol' fluorescent bulbs. I found that they offset the gold, pine wood ceiling I have. But then, I remembered the health effects of those lights when used alone for long periods of time. I was wondering if you still like the afore mentioned lights and do you think they have close to the full spectrum of color in them which is said to be very beneficial to our health?

I'm hoping if I have enough of them and they are positioned advantageously I will not have to worry about that yellow ceiling or even my gray-green walls. What do you think?

Thanks for your help!

Val, the lights I use are full spectrum. There are many degrees of color rendering accuracy in the full spectrum area. There is a designation called color rendering index or CRI. If a bulb is rated over 90 CRI it's considered full spectrum. The Lumichrome bulbs I use are rated at 98 CRI, the very highest available. Daylight is rated at 100 CRI.

The color of your ceiling and walls shouldn't matter as ling as the bulbs are in white fixtures. If the lights are reflecting directly from the ceiling you would need to employ some sort of reflector housing to eliminate this since the color of a reflective surface will compromise the color temperature of the bulbs you use.

Hope this helps.

You might want to bring some photos of your studio to Atlanta and we can discuss this further.

:thumbsup:

Oh you are the bomb! That makes it very clear. I was not giving any credit to the housing/reflectors that the light is mounted in and I will make sure they are white and wide to throw lots of the CRI 98 light.

I will bring pictures of the studio to Atlanta, thanks!

Marvin--

I've always understood the temperature of a north light to be around 6500K to 6800K, approximately in the middle between a regular fluorescent light and 5000K.

I've used the Lumichrome tubes in the ceiling of my studio for years, supplementing my northwest window, and found them to be generally very good. However, a complicating factor for me is that when I paint under any single overarching wavelength of light all day, my eyes get tired, especially at night--to the point where color discernment goes completely South. So I've used a cheap reflector on a stand and bounced another wavelength--sometimes regular tungsten household bulbs, sometimes the Sunwave corkscrew bulbs, sometimes blue-coated bulbs (whatever feels right)--off of the ceiling into the overall Lumichrome illumination. It's really just a "trace" of another wavelength, but the mixture helps immensely in avoiding the eye fatigue over long sessions.

Thanks as always for your thorough research and generosity in sharing it.

Best--TE

Tom, I haven't experienced the eye fatigue you describe, but if I do I'll certainly apply your remedy. I'd never have known about this solution if I hadn't shared my knowledge first. What goes around comes around. Thanks!

[QUOTE=Marvin Mattelson]
In addition I've never seen any lights that are better.

Here is the description from their site:

Lumichrome

The 5000k bulbs do not match the color of the light coming in from my north window. What can I say? The 6500k bulbs, on the other hand, are a perfect match. I love painting under these bulbs. The 6500k bulbs are used in the textile industry where color matching is hyper critical. Artists have always sought the cooler light of the norther exposure. Also, the CRI of the 6500k bulbs is higher than the 5000k ones. 5000k is a standard in the printing industry which is why they suggest these for artists.

I find that the manufacturers of bulbs (or anything for that matter) are usually wrong when suggesting what is right for the artist. I'd rather take the word of an actual real live artist myself. For example Soltek recommends 3500k bulbs which are ridiculously yellow-orange. They've convinced galleries and museums of the superiority of their bulbs. You can't even see the color of the paintings, it's so distorted. The Ott 5000k bulbs appear very green to me. Caveat emptor!

When all is said and done, you might prefer the 5000k.

I definatley agree with you about the OTT lite... they are terrible. I bought one to use for a model stand to simulate cool window light for my classes and all I get is green. It's terrible.

HI all,

I recently ordered a pair of 6500 bulbs from www.1000bulbs.com, and I just love them. They are the spiral shape and are very strong, 42 watts (equivalent to 150w), 2800 lumens, and best, they screw into a regular light socket ( with a little extender) . They are really cool, literally and figuratively.

The mfg is TCP, consumer info 800-771-9335.

AWESOME!!! I have been looking for something like this!!!

I just placed an order!

Thanks Chris!!!
Tony

Comparing CRI among fluorescents
 

Hi All,

Holly Snyder introduced me to the Diffraction Grid method of visually comparing the CRI (color rendering index) of light sources, and I got a grid sheet of my own to compare my findings with hers.

I use JUST Normlicht Color Control Daylight 5000 fluorescent tubes in my studio. They are 36 watts, 5000K, and 48 inch T-8 tubes, and are rated at 98 CRI. This is as good as a fluorescent light can get.

I don't have a north light window to match, so 5000K is comfortably cool for my purposes. Marvin's argument for 6500K illumination seems valid for the purpose of matching a north light, which would be cooler due to the dominant illumination coming out of the blue sky.

For comparitive purposes, I've grouped four diffraction grid spectrums into one chart. From the left, the first two strips are from my camera, and the last two are from Holly's camera. I believe we both have the same camera (Nikon D100), and the same brand diffraction grid sheets. I shoud note that the spectrum looks very different to a camera than it does to the naked eye. Cameras have their limitations.

The 5000K Just Normlicht, and the 6500K Lumichrome appear to be about equal and genuinely 98CRI each. The 5000K Lumichrome, is not as good as the JUST Normlicht, as it shows more gapping in the spectrum. A Standard cool Philips tube is clearly way down on the CRI scale as there are wide black gaps.

So if you need to match north light, the 6500K Lumichrome tubes That Marvin uses look best. If you prefer 5000K, then JUST Normlicht is your best option.

Garth

Marvin,

When I was setting up my new studio I researched lighting extensively. Hopefully the following will help. Color Rendering Index is very important as is the Kelvin temperature. Both must be considered together to get the best light compromise...and it is a compromise. North light is about 7500 Kelvin according to some sources and tends to be more blue and balanced in spectrum than south daylight. However, the reflected color from your studio walls and ceiling will influence the color you see. Hence my statement about chosing the best compromise.

Lumichrome flourescent bulbs at 6500 kevin and 98 CRI seem to be the best compromise of both criteria for bulbs on the market for the studio artist. Going with lights that are between 5000 and 7500 kevin and with a CRI greater than 92 should work well in any case.

If you want to get very technical you can do prismatic spectral analysis to verify that your new lighting reasonably matches your north light. In the end though it will come down to what pleases you as your art will ultimately be displayed in lighting that will be anything but north light.

Wish you success.

Garth must have posted his reply as I was writing mine. Way to go Garth. Your diffraction grids show that there is a reasonable spread of light Kevins that can be chosen.

Chris, thanks for posting that link for the screw-in 6500K bulbs. I have two light stands in my studio that I like to move around depending on what I'm doing and it would be great to have decent bulbs to put in them. I'll check out the TCP bulbs.

Chris, I checked your link and could not find the 6500K bulb. What was the CRI for this bulb?

http://www.1000bulbs.com/search.php

You'd have to ask them about the CRI

And
 

And here's what happens. We paint under perfect lights. Then (some of us) send our works to galleries who place them under hot spots about 3800k. Then someone buys them and you have no control or idea of how they will be hung.

This was the long view when the CAA's began discussing this 10 years ago. Perfect circumstances are for perfect worlds. Compromise is the reality. As many of you know, the galleries may never even give you the name of the buyers. Selling directly to a portrait client, you can nudge them and try to educate them-but everyone won't listen.

The bulbs also change their temperatures as they age-just like in the tanning booths. But take heart, Sargent, Whistler, Monet, Titian, Zorn, Sorolla and Vermeer did okay without these.

They all painted in the daylight, either indoor or out, right?

I have read that Da Vinci recommended painters to shade there studio windows with thin white linen to dim the light and even put an extra layer along the sides of the window to make the light extra soft. I came to think of this information some months ago when I had trouble seeing values because the light was too strong over my easel. I then changed the direction of the light to a reflection from the white wall and felt that it was much easier to judge the light values of the colors.

One thing that I have noted is that paintings with a good value scheme always show well no matter what light conditions they are seen under.

We could mark our paintings to inform the costumers about the optimal light to be seen in. Some of them might be interested I think.

Allan

Cools
 

Despite all the tests etc the companies do, I desire to see more purples and blues in the shadows. I feel natural light does this better. Many modern painters work seems hot to me-I blame electric lights. These old artists had nicer cools. What do you think Bill and Michael?

When I paint outside on cloudy days the mids and cools are lovely. I'm designing my lights for my new studio and all this is most interesting.

I don't mean this to sound like an incredibly stupid question, but... on a very nice day does anyone just roll their easel and reference (not live models) outside?

Outside
 

Well, outside the light is still directional even on a hazy day. Maybe I don't understand the question..help, help...

Beth, as the saying goes: there's no such thing as a stupid question. I think it would be ill advised to change the source of light you're working under in the middle of doing a painting. The color relationships would change to some degree. To what degree, would depend on the quality and temperature of your studio bulbs.

I've heard many stories from artists, particularly back before the advent of color corrected lights, who worked all night to finish a painting, under artificial lighting, and were horrified to see their results the following morning, in the light of day. Also, wouldn't this require you lugging your computer and monitor outside as well?

How True!
 

Marvin,

How true!

I've been one of those work-all-night-and-be-horrified-the-next-morning-by-the-light-of-day artists, every time I worked at night, until I installed those 98CRI Fluorescents. They really work!

5000K 98CRI
JUST Normlicht Color Control Daylight 5000

6500K 98CRI Lumichrome (Marvin's Choice)

Garth

This makes sense, but we had one of those lovely early spring days and it was just so tempting to just roll out on the deck - since I use a laptop the computer was not a big deal.

I haven't been able to get accustomed to working with oil under artificial light. I think I have them hung incorrectly, or it's my old age eyes. I'll have to re -read this and see what I am doing wrong!

OK, here's a (I should know the answer but I don't) question - does anyone know the measurement of halogen lights? Because of a low ceiling and it being white, I bounce two halogen lamps off of the ceiling for illuminating my canvas. I recognize a difference in color when I take my paintings outside.

I may experiment with other lamps that I can bounce off of the ceiling.