Violation of Inverse Square Law: How can this be?

[FJ and G]

Reg. the MR article (June04) on multilevel lighting, I have 2 questions.

But first, I'd like to state that overall, the article was outstanding and will likely help me as I'm now constructing multishelf lighting. The comparison of flourescent bulb spacing was an outstanding "scientific" experiment that clearly showed the gaping effect that left dark spots.

1. The article stated that flourescent bulbs, unlike incandescent, do not follow the inverse square law of light (e.g., if you double the distance from a light source, the lighting decreases by a factor of 4). Light is light. How can this be?

2. On the lower shelving, the flourescent bulbs are shining directly on the plastic trains and structures. No mention was made reg. the degredation to the plastic caused by flourescent lightwaves.

Lastly, I realize that flourescents don't heat up like incandescents, but the blue cast they leave on the layout is rather depressing. Incandescent or halogan-like lighting gives a much more cheerful cast, but is somewhat yellowish. A mix of the 2 lighting would be optimal, IMO.

Dave Vergun

[Anonymous]

Your point number 1 is interesting - light is light, regardless of the source, so I don't understand either. Number 2 - I think fluorescent lights pose the least danger to plastics or other "fading", especially compared with high-intensity halogens or sunlight. In all my years on the "cubicle farm" have never seen fabric or plastics faded by the fluorescent lights. [;)]

Andrew

[lupo]

Dave
fluoresent tubes are available in many different "colors" = shades of white, from daylight to a warm yellowish glow, and it is the ultra violet component in light is responsible for the degradation of styrene and other plastics. There are FT's available with blocked UV, but the UV coming out of ordinary tubes is just a fraction of the UV coming to us through sunlight and IMO do not cause plastics to degrade.

[ndbprr]

It could have to do with a couple of things:
1. In an incandescent bulb the light source is basically a point with light radiating in all directions from it. A flourescent puts out light over the length so there are infinite points creating an overlapping effect
2. It could have something to do with the wavelength and what part of the spectrum the light is coming from.

[dknelson]

I can say that flourescent lights have badly faded the book jackets on my railroad book library. Comparing the spine with the cover shows dramatic fading and these books have been under flourescent lights exclusively. With some of these books now selling for close to $200 each on the collector's market this is somewhat depressing.
Dave Nelson

[Anonymous]

David, I agree. Light is light. The inverse square law is a physical property of light. The source of the light doesn't change that property.

In my studio, if I diffuse a hard light source, it spreads the light out and it will not reach as far as the bare instrument. However, if you measure the light intensity from the front of the diffuser( the source), you will find that the inverse square law applies as you move away from this "source."

Dennis Brennan

[FJ and G]

Incandescent light sources also can be fitted with diffuser filters. I installed one in my shower unit. The advantage of diffusers is that it softens shadows, unless you are trying for a shadow effect.

The Inverse Square Law, like the speed of light, is an immutable fact. Perhaps MR could add a small correction or a clarification in the next issue.

However, I do want to reiterate that overall, the article was outstanding, as was the entire issue.

dav

[mondotrains]

Hi Dave,
I had read that flourescent bulbs give off UV light and considering I've avoided getting a lot of sun (because of the skin cancer potential), I didn't want to then deal with UV light in my train room. Therefore, I purchased clear plastic tubes which are available for flourescent bulbs which filter out most of the UV light. They are only a couple of dollars each and easily slip over the bulbs before you install them.

Also, the lighting store salesman advised me to buy mid-grade floursescent light fixtures because the so-called "shop" lights you can get cheap at home improvement stores have a cheap "generator" that will cause the light to "flicker" and drive your eyes crazy. I know he was correct because my eyes go crazy at my buddies house where he has installed cheap shop lights. After a few hours, I have to leave because I've got a headache. My 4-foot fixtures cost around $40.00 each but considering they're a one time investment and the resulting improvement in lighting, they were worth the investment. Installing better bulbs that are made for "kitchens and baths" gives a softer light that the cheaper "shop" bulbs. Believe me, the difference in the fixtures and bulbs makes a huge difference and is worth the cost. Go to a lighting store and a salesman will show you the difference.

You're right about mixing the flourescent light with incandescents. I have both in my train room and generally only turn on the flourescents when I'm working because the incandescents generate a lot of heat and I obviously don't want the extra heat when I'm working. I turn on both the flourescents and incandescents for visitors and during operation for the improved lighting.

Hope this helps.
Mondo

[FJ and G]

Mondo,

I too have sensitive skin & didn't even think about this problem. I'd imagine that black lights are even worse.

One other negative thing about flourescents is flicker; known to cause epileptic seizures, not to mention being annoying to the rest of us. Incidentally, the reason you often see 2 flourescent lights together is to reduce flicker by phasing them at different wavelengths to cancel the flicker.

dav

[mondotrains]

Hi DAV,
I didn't know that flourescents could cause epileptic seizures but I agree they can be annoying. Like I said in my post, a better fixture will significantly reduce the flicker....in fact the flourescent lights in my train room "feel" like incandescents.
quote]Originally posted by FJ and G

Mondo,

I too have sensitive skin & didn't even think about this problem. I'd imagine that black lights are even worse.

One other negative thing about flourescents is flicker; known to cause epileptic seizures, not to mention being annoying to the rest of us. Incidentally, the reason you often see 2 flourescent lights together is to reduce flicker by phasing them at different wavelengths to cancel the flicker.

dav

[Anonymous]

OK. I like to think I am well versed in the sciences. But this is way over my head. Can somebody please put in baby talk terms what this thread is about????

[MAbruce]

QUOTE: Originally posted by FJ and G

1. The article stated that flourescent bulbs, unlike incandescent, do not follow the inverse square law of light (e.g., if you double the distance from a light source, the lighting decreases by a factor of 4). Light is light. How can this be?

This is over my head, but your concern makes sense (somehow... [%-)] )

QUOTE:
2. On the lower shelving, the flourescent bulbs are shining directly on the plastic trains and structures. No mention was made reg. the degredation to the plastic caused by flourescent lightwaves.

I would think it would all depend on what kind of bulbs you are using and how close they are to the structures. Some bulbs throw off more ultra-violet rays because they are made to simulate sunlight.

QUOTE:
Lastly, I realize that flourescents don't heat up like incandescents, but the blue cast they leave on the layout is rather depressing. Incandescent or halogan-like lighting gives a much more cheerful cast, but is somewhat yellowish. A mix of the 2 lighting would be optimal, IMO.

I use a special florescent bulb made by GE labeled “Kitchen and Bath”. It sounds like Mondo is using the same bulbs. It really does make a difference. I took these two pictures using the “indoor” setting (usually intended for incandescent lighting) on my digital camera:





I tried to use the three special “florescent” lighting settings on my camera, but those pictures turned out too reddish (obviously over-compensating for the blue tone that fluorescents usually throw off).

I really like these blubs!

[cmitcham]

QUOTE: Originally posted by Grayhound Challenger

OK. I like to think I am well versed in the sciences. But this is way over my head. Can somebody please put in baby talk terms what this thread is about????

james:
<sarcasm>
when you walk in a room, flick the switch and the light comes on. if it's too dark to see what you're after, get a lamp and put it close to what you need. any more time studying the science of light is time that could be spent building/running trains.
</sarcasm>

calvin.

[Anonymous]

Thanks Calvin

[ndbprr]

Well the aspects are important to realism. ideally we would have shadows that replicated what the sun does through the course of a day so we would sense early morning or late afternoon when operating. Flourescents just don't give much in the way of shadow detail and it does have an effect.

[FJ and G]

Off-topic but Bruce's abandoned track thru the tipple is really neat. I'm modeling an abandoned spur and nice to see someone else doing something similar.

Also, agree that your lighting looks good. All lights have color rendering numbers on them that you can compare with the northern sky at noon, which is the benchmark used to compare artificial with natural "daylight".

dav

[Anonymous]

Allright,

While risking putting my foot in my mouth, lemme give this one shot:

I don't have my university physics book with me to give the exact relationship, but the fact that light intensity does not vary with the inverse square of distance for a florescent light has some merit if it is implied that the light comes from an infinitely long "bar" or light as opposed to a point source. One way to see this is to think that the further you are from the bar of light, you can see more of it head-on (you can now see parts of the light source that are further away from the centre where you started moving from), hence there would be more "light source" visible to you than, say, from a single point source, so the intensity would not decrease as much (in fact, I think in this case the intensity drop is inversely proportional to distance as opposed to the inverse square).

However, the farther you are from the fluorescent tube, which is in all practicality finite in length, the more it acts as a point source, in which case the intensity would follow the inverse square rule.

In the end, it's all up to interpretation, and I'm a bigger geek than I was yesterday.

Calaille

[eng22]

After reading this entire thread i am left with the following key points:

1. MAbruce has an awesome layout!
2. Kitchen and bath lights work best, because MAbruce has an awsome layout![:D]

[mondotrains]

Hey Craig,
You missed one other point. Buy a better flourescent light fixture and Don't buy cheap shop lights unless you want your buddies to leave early with a headache.

Mondo

QUOTE: Originally posted by eng22

After reading this entire thread i am left with the following key points:

1. MAbruce has an awesome layout!
2. Kitchen and bath lights work best, because MAbruce has an awsome layout![:D]

[Anonymous]

For those who want to know what the Inverse Square Law of Light is . . .

The intensity of light on a surface is proportional the one over the square of the distance from the surface to the source.

Explanation . . .

Picture a candle with the flame happily dancing and giving off light. The amount of light created at the candle is constant and is moving away from the candle in all directions at the speed of light. The amount of light is constant at any given distance away from the candle but the surface area grows as a square of that distance. So now picture a basketball around the candle. Add up all the light shining on the inside surface of the basketball and you have the amount of light given off by the candle. Now increase the size of the basketball by a factor of two (doubling the radius) and the surface area goes up by a factor of four. But the amount of light shining on the inside of this larger ball is still the same. However, the intensity of the light per square foot has dropped by a factor of four and this is what you perceive as brightness.

This is what the inverse square law of light is all about. It is also true, I believe, for all other energy sources that radiate in all directions such as sound; however, heat will not obey this because heat wants to travel in a specific direction. I hope I didn't bore anyone with this and I hope you all enjoy your model railroading. - Ed

[Anonymous]

Warning ! This will not be technical, scientific, and hopefully not boring.

Cheap fluorescent fixtures are also dangerous for anyone working w/ table saws, chop saws, radial arm saws and any other tools w/ spinnning cutters because their flickering can create an optical illusion - in other words, it can sometimes be difficult to tell if a turned off machine's blade is still spinning. There are documented cases of lost fingers and worse from such a situation.

Also, fluorescent fixtures, esp. cheap ones, and those that have an accumulation of shop dust (which may be flammable material), have been identified as the cause of fires in shops, garages, etc. Some very expensive car collections and shops have been reduced to cinders because the fluorescent lighting was left on for extended periods of time, unattended, until the fire department showed up.

The recommended bulbs for replicating sunshine have a CRI of 90, which is a measurement of color shift when an object is illuminated by a light. CRI ranges from 1 to 100, with natural light and incandescent light equal to 100. Kitchen & Bath has a CRI of 70. Lower CRI #s are typical of both warm (53 CRI) and cool (62CRI) whites. In wood finishing shops C-50 bulbs (85CRI) are recommended for balanced and accurate color rendition and matching of finishes. The lower CRI rated bulbs will cause muted and odd looking colors. The higher CRI bulbs cost a bit more than the standard warm or cool ones more commonly found in shop fixtures.

If you don't have your fluorescent bulbs protected by a plastic diffuser or grill work, consider putting the clear plastic tubes or sleeves (avail. at home centers) over the bulbs. If you should strike one of the tubes, the glass shards will be contained in the sleeve and not rain down on you and your scenery.

Hope this sheds some more 'light' on the subject.

[locomcf]

From what I remember, the 'standard' cool white fluorescent tube emits a broad spectrum of light colours at a colour temperature of 3600K. These tubes emit more UV light than incandescent bulbs, which is probably why they are said to cause fading (relative to incandescent). If you want to avoid the UV, there are options such as tri-phosphor and quad-phosphor tubes which emit light in (essentially) just 3 colurs and 4 colours (respectively).

Fluoro tubes also come in different colour temperatures, such as 5000K and 5600K (as well as others), each of which gives a different look. Generally, 5000K is considered to be more like "daylight" than 3600K. Stores that want their meat to look 'redder' and their fruit to look fresher will often chose a fluoro tube which 'enhances' the colours. Modellers can do the same thing on their layouts.

Unfortunately, Tony's article didn't explain all this in great detail, although he does mention it (saying he prefers 'cool white').

I'd like to hear more about the "Kitchen and Bath" lights mentioned by MAbruce. I have never seen them here in Oz.

Ron

[FJ and G]

Ron,

That's a good point about stores wanting their meat to look redder. Specialty stores dealing in jewelry and cosmetics avoid the cool white flourescent bulbs. If there's any moral to this thread, it is that modelers who desire true color rendering close to natural light, should not skimp on price? Get some good lighting so your true colors show up.

DAV

[GerFust]

All:

This was an interesting topic. So I took it as a challenge to understand MRs statement.

Sorry if this was mentioned above, but some we research shows that fluorescent lights follow the "Inverse-linear law". For more information see http://www.npdi.dcc.ufmg.br/disciplinas/reportagens/imagens/Morepower%20to%20you%20(inverse-square%20law%20to%20sound%20and%20lighting).pdf.

Basically, think of the fluorescent tube as a row of small light points. each point emits light according to the inverse square law, but the area covered by each point overlaps with the next several in each direction. The net affect is that light coverage is inversely proportional to the distance from the tube, and not the square of that distance.

-Jer

[Anonymous]

After reading some of what's on the net, a few points were recalled, light from bulbs or tubes isn't coherent lite as with a laser. As it moves away from it's soarce, the beam widens and must cover more area unlike a laser beam which remains together over a longer distance and concentrates its' light only on a small area. You can compare it to water from a hose. tighten the stream, and it remains very dense and concentrated, open up the nozzle for a fine spray and the stream becomes much less dense while covering a much wider area. Actually, even light from a laser, traveling thru a fiber optic cable must be regenerated every few miles to maintain its' level or intensity. Sound, which really comes from the same spectrum as light, just at the opposite end, must also be regenerated, but more often. The only variable here seems to be the color of the light in the comparison. Incondesant lite is really yellow or a very off white and probably doesn't maintain its' intensity as long or over a given distance. White, on the other hand, even at low power ratings, is very intence at the soarce, and therefore will maintain a higher level of that intensity over the long haul.

[Anonymous]

Guys,

This thread from the Atlas forum contains some of the best explanations on the topic of flourescent lighting I have ever seen. There is a posting from a bona fide expert - a guy who worked at a plant designing and testing flourescent tubes!!!

http://forum.atlasrr.com/topic.asp?TOPIC_ID=42210

The second is a good explanation of color temperature:

http://www.edbergphoto.com/pages/Tip-fluorescents.html

Enjoy!!

Guy