Shop fluorescent lights

[Gerald Ross]

A friend is building a shop (for pottery making) and wants fluorescent lighting that is like daylight for colors. What type is best, and do they make these in T8?

[John]

You may find that a mixture of tube types (Daylight White, Warm White) gives a truer color appearance than the Daylight White alone.

You probably do NOT want Warm White only, as most people think they are too pink.

Since color is subjective and artists are more critical of lighting color, you probably need to have the friend take samples of favorite colors and see how they look under each bulb type.

It may help if you can find a spectrum chart at the manufacturer's site.

John

[Lew Hodgett]

If you are trying to duplicate natural light with artificial sources, you can't get there from here without spending lots of money.

People attempt to do this with what is known as a "Color Table", which is relatively small.

They consist of a mix of lamp types, operating at controlled voltage and temperature as well as being operated over a very tightly controlled life span.

OTOH, if you simply want to obtain a pleasing to the eye color rendition of the pottery, that is another matter.

As I once told customers, if all you need is a consistent color from batch to batch, that does not require an expensive lighting system.

If true pink looks like purple under your lights, as long as it is the same color of purple every time, it is not a problem.

Exact color rendition is VERY expensive.

Lew

[Steve Hall]

What you want is a bulb with a high Color Rendering Index (CRI) value. This is a percentage, the proximity of the light color to natural sunlight. Anything 92 or above is very good, and you can find 48" long ones at the local home improvement place for about $5 each.

I purchased Philips brand bulbs with a 92 CRI for a 4-bulb fixture in our master closet and it would fool someone into believing it is a skylight. With four bulbs it is very bright, the color is very white and clear, although my wife sees it as a fraction blue....

...that's the caveat, sunlight from directly overhead *is* blueish, which is why our fixture look like a skylight. Many people have become accustomed to reddish incandescent light and prefer the color of morning or evening sunlight over noon. In these cases, very high CRI bulbs can seem too hot, although they are no where near as blue as the typical fluorescent bulb. For fashion and art, lighting sometimes is intentionally forced to the red side of the spectrum to convey the feel of evening or candlelight and to exaggerate reds. Likewise for film, Kodak is often preferred over Fuji for the same reasons.

The bottom line is some prefer to *match* the shop/studio conditions to the final resting place for the piece, be it art or furniture. However, my preference is to go with *accurate* rendering of sunlight since it is fairly in the middle and a safe hedge against being too far either way. Plus, it feels more like outside, perhaps what your friend's desire is, too.

[Bruce T]

Gerald:

Actually, "daylight" is about 6400 degrees Kelvin and yes, they do make T8 bulbs close to 6400 degrees K (maybe it's 6200K, I don't remember). Get them at Home Depot, I think they're in the blue-ended Phillips container. Most people don't like them in their home, because they seem too "cold" (i.e. blue). Actually, they really appear too hot (blue is "hotter" than red), but that's people for you. Anyway, we're sort of used to incandescant lighting (standard light bulbs) which are really kind of orangish, so when we see indoor lighting that is the same color temperature as daylight (6400K), it looks way too blue to us. I use the 6400K bulbs in the laundry, because it makes it really easy to distinguish between navy and black socks.

By the way, a lot of people say that they want "daylight" lighting, but sometimes that's not really true. If you friend is going to be making pottery that will be used or displayed outdoors mostly, then daylight color rendition is probably best. But if they are making pottery that will be used and displayed indoors under incandescent light, then maybe they really want lighting that is closer to incandescent, i.e., 3400K (these are in the reddish-ended Phillips containers).

Anybody who does any semi-serious photography has to learn this stuff if they want to make decent photos.

BruceT

[Chris Friesen]

For accurate colours you want a high CRI rating (100 is "perfect"). Totally aside from the CRI value is the colour temperature, which determines whether the colour is biased towards red or blue.

One very high quality T8 bulb is the Philips TL 950. This bulb has a CRI of 98, and a colour temperature of 5000K which is quite white but not as blue as a 6000K or 6500K bulb. They also have other bulbs at different temperatures with somewhat lower CRI ratings.

One step down from this there are quite a few manufacturers that make bulbs with CRI values of 84-86 and colour temperatures ranging from

3000-6500K so you can pick exactly what you want.

Chris

[Gerald Ross]

Thanks, that makes a lot of sense.

[Gerald Ross]

Thanks to you all for your insightful replies to a mostly off-topic question.

[beecrofter]

After you sort out your mix of flourescents consider adding a few small incandescent lamps close to the wheels so that rotating parts do not look stopped due to the flicker .

[Gerald Ross]

Good thought! I never thought of that. Thanks.

[Scott Lurndal]

Look for Chroma 50 (sometimes known as C-50) bulbs. They have a color rendition index pretty darn close to daylight. The Borg carries them.

scott

[Robatoy]

Or wire every odd one out-of-phase.

[Chris Friesen]

The Borg doesn't carry them around here. Closest thing they have is the Philips "natural sunshine" in a T12.

Chris

[Steve Hall]

Those are great bulbs, that's what I use and they have a CRI of 92.

[Wes Stewart]

On 17 May 2007 17:28:23 -0700, Robatoy wrote: .

How are you planning to do that?

[Tom Veatch]

Maybe use both legs of a 240v branch? Each leg is 180 deg out-of-phase to the other leg and 120v to neutral. Would require 240v breaker and 4 wire cable (3 conductor + ground) with alternate fixtures fed by opposite legs.

Or use two 120v circuits fed by breakers on opposite legs of the service at the breaker box.

Not sure that would stop the stroboscopic effect since both legs of

240v two-phase service go to zero voltage at the same time. Now if you had 3 phase service (three hots with 120 degree phase differences) you might have a better shot at it. Two out of the three phases would be at non-zero voltage at all times.

[Mike M]

Just go with electronic ballasts. They operat at about 25KHz. The T8 lamp is probably the best value of the fluorescent lamps if color is important, but as was previously stated if you want the highest color rendering lamps it will cost you about double per lamp. Mike M