TheRailwire
General Discussion => DCC / Electronics => Topic started by: Dave Schneider on September 28, 2012, 05:12:50 PM
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I am getting to the benchwork building stage and my plan is for a shadow-box type arrangement with an upper lighting valance. At one point I thought that T-8 fluorescent tubes were the way to go, but now I am considering LED strip lights. One primary advantage I see is their light weight, which allows for less robust valance construction (like maybe foam core instead of masonite/wood).
In searching for LED strips, I notice a wide variation in prices from the $20 range to $100+.
I think what I want is something like this, a lexible strip that can be cut to different lengths: http://tinyurl.com/8d5nc53
Or do I need to go to "high power" LED strips?
There are so many different kinds now it is hard to figure out what is needed.
Thoughts? Vendors? Model Numbers?
Best wishes, Dave
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Only thing I can add is that light is measured in lumens.
And you probably need the really expensive LED lights to be happy.
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OMG, LED lighting is so dynamic right now. At the moment it's one of those things that anything you do will be obsoleted tomorrow, at half the price you paid yesterday. :scared:
As far as the LED strips, yes, you'll need high brightness, although I recommend a dimmer/controller. My concern about the eBay lights you're shopping is whether they will be available tomorrow. Seriously, the Chinese suppliers for this stuff come and go like crazy, and getting brightness and color consistency between orders is nigh impossible. Super Bright LEDS (http://www.superbrightleds.com) is going to be more expensive than the eBay discounters, but their business plan is apparently to lock-down suppliers so they can catalog consistent, higher-quality product.
I am going 100% LED for the Gibbon, Cozad and Western... in fact, for the whole building. I'm not planning valance-style illumination; the current plan for scene illumination is track lights with GU16 gimbal fixtures (http://www.lowes.com/pd_372814-53027-EC1596WH_4294925665__?productId=3646660) (the small, normally halogen reflector, 110V type) using 40 or 50W-equivalent dimmable LEDs. Believe me, I've shopped the zillions of online LED stores, but the best I've found so far is the Philips GU16 at Home Depot (http://www.homedepot.com/Philips/h_d1/N-25ecodZ5yc1vZ15b/R-203321687/h_d2/ProductDisplay?catalogId=10053). There are a lot on the market right now which are not dimmable. I do have samples of LED spot/floodlights that look like traditional consumer PAR30 and 38 bulbs. These are impressive for brightness and color, and reasonably-priced. http://www.wholesaleled.com
Room lighting will be a combination of LED "can" lights and track lights. I found a can-style downlight (http://www.homedepot.com/Lighting-Fans/h_d1/N-25ecodZ5yc1vZbvn5/R-202823462/h_d2/ProductDisplay?catalogId=10053&langId=-1) at Home Depot which looks really, really good in my tests.
For "mood" lighting I am reaching into the stage lighting catalogs for LED "wash" light bars and PAR can spots. These aren't cheap, but are getting better. The advantage with these is the integrated DMX512 control bus, which means that a relatively inexpensive ($75-150) stage lighting controller can be used to control all the room and display lighting, even via computer. Non-stage system lights like the track lights and downlights can be controlled through "dimmer packs", cheap (~$60) clusters of DMX512-controlled dimmers that you plug regular lights into.
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I am going to wait a while on LEDs .. I don't want the lighting to cost more than the layout ..
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Mike,
Thanks for the info. Very helpful. Any thoughts on whether this item is too good to be true (other than not shipping to Alaska!):
http://tinyurl.com/98hetxo
It is much less expensive than this one from Superbright:
http://tinyurl.com/9rmszo5
I have no feel for the different LED types.
Best wishes, Dave
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Those LED strips are not powerful enough to illuminate an entire layout on their own from ceiling height; you'd need several strips in parallel to build up the brightness to an acceptable level, by which time you've spent a fortune. Plus they do not have consistent color temperature. You are much better off looking at "proper" LED fixtures. My pick would be resessed units (http://www.homedepot.com/Lighting-Fans-Indoor-Lighting-Indoor-Ceiling-Lighting-Recessed-Lighting/h_d1/N-5yc1vZbvlwZ1z115g2/R-203010504/h_d2/ProductDisplay?catalogId=10053&langId=-1&storeId=10051). They are seriosuly bright, have a good color profile (very close to tungsten), and can be dimmed smoothly without flickering. I use them to illuminate my office/workshop, and would use them for a permanet layout in a heartbeat, if I started one tomorrow.
Those flexible strips are great, however, for lighting your backdrop. Leave a gap between the layout and the sky board, and run strips along the bottom of the gap. Use colors for different effects, like orange/red for sunset, blue for twilight, or spend a little more on RGB strips which will generate any color you want. By the way, I have purchased those LED strips for as little as $30 for the 16-foot 300-LED version on eBay. Run searches and sort by price--you will be amazed by the range.
I am going to wait a while on LEDs .. I don't want the lighting to cost more than the layout ..
Don't wait too long, because they save enough energy to pay for themselves in a few years. Plus, those recessed units are getting very cost-effective.
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I'm no expert on LED lighting so won't be able to add much here, but I would reiterate that the two main lighting factors you should consider are 1. overall brightness (lumens) and 2. spectrum (effective temperature).
To put this in context, I am using T8 fluorescents that have a brightness of ~2800 lumens per 4ft bulb and (in my case) a color temperature of 5000 K, which Philips calls daylight. I have 10 2-bulb fixtures in a 10x20 garage for a total of 56,000 lumens (from 640 watts of power). As ambient light goes, it's quite bright, but I find that when I'm looking at a train on the layout, it could still stand to be brighter, so it's not too much. (The figure you really care about is lumens/m^2 falling on your layout, but for linear lighting, and in the absence of too many dark surfaces, the light is fairly uniformly distributed). I really like the 5000 K color temperature, but some find it too harsh. Spectrum is a pretty subjective preference, so you'll just have to try a few types out to see what you like.
For comparison, the strips you link to are ~800 lumens/m, which as DKS points out, is rather dim. I think you'd want about 60-70 meters of these to get the same light output I'm getting (unless you really focus on lighting the layout and not the room). At $100/20 m, that's not crazy, but you'd have to think about where you'd put it. If your trailer is ~10 x 20 ft, and you have 200 ft of light strips, you'd have 10 strips running the long length of the room, one per foot. Only you can decide if you like the spectrum.
Hope this helps,
Gary
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Oh... almost missed it... the eBay listing is for four reels of the stuff, not one. Wow. That is cheap. Plus, the eBay reel is rated 4X the brightness, 800 lumens/meter, versus 200 lm/m (calculated) for the Super Bright reel. Super Bright really needs to get with the program on pricing; they were pioneers but seem to be resting on their laurels the past year or so.
800 lumens is very roughly equivalent to a 50-60W incandescent. So each reel of the eBay tape would in theory replace five 60W bulbs. It looks like a deal to me. The only caveat I can offer is firsthand experience with some Chinese eBay'ers overstating specs. It's an easy trap because of generations of equating watts with brightness, now we have to learn a whole new system.
David is right, the strips probably won't work for room lighting, but I think they would be more than fine for valance lighting.
"Warm White" is somewhat standard nomenclature for a color temperature of 3000° Kelvin (3000K), for a yellowish white pretty darn close to a conventional halogen bulb. That is usually my choice, and is where most consumer-grade LED replacement bulbs are going. You'll notice that the Super Bright "whites" are available in three color temps, 3000K, 4500K and 9000K. 9000K is almost blue, and IMO is that annoying white-but-not-really of the early "white" LEDs that now seem to be called "pure white". 4500K is called "daylight", probably because the white is very close to the "daylight" florescent tube color (as Gary mentioned), or only slightly bluish.
As Gary alluded, I'm one of those who find 5000K too harsh, and it is a subject of debate between my wife and I for the studio/layout building. Being an artist and experienced in the printing trade, she gravitates towards the 5000K as being the accepted "neutral" within the industry for color balance. Since I'm the family electrician, guess who wins this one? :D
If you are planning a lot of photography, you still might want some 4500-5000K in the mix. The 3000K alone will make photos appear yellowish, although these days you can certainly correct that in post-processing.
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Might find something helpful here:
www.4dpnr.org/articles/Layout_Room_Lighting.pdf
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Thanks everyone. This is quite a bit of information to digest, but I really appreciate the input. That was a great resource Chris.
As for my situation for those who are interested, I have a 10x20 layout space. I currently have four 2-tube T-12 (?) ceiling fixtures that provide adequate illumination for the room. What I pondering is how to illuminate just the layout space. The distance between the lights and the layout surface will be relatively modest, something like 15 to 18 inches, and the depth of the scene will be about 2 ft, and I have about 50 ft of run. While the LEDs can be expensive, a run of 4 ft fluorescent tubes aren't cheap either. Time for some calculations.
Suggestions still welcome!
Best wishes, Dave
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Dave,
As per several comments about color temperature, my cohort and fellow take-the-modules-to-the-show crazy Gregg Cudworth and myself put our heads together to standardize the color temperature of our modular lighting, and decided on 5000K.
I got a terrific deal on 5000K 25W (100W incandescent equivalents) Compact Fluorescents at The Home Depot and decided to try them out. At first I was put off by their "harshness", which translated means they were noticeably much more blue than the other bulbs in my layout room. I decided to change out all of the bulbs to be consistent, and as my eyes became used to the color, things started looking "right" to me.
Being an artist and photographer, and very conscious about light temperature in digital photography as it relates to digitizing my artwork, I decided to take some test shots of my "daylight" lit layout, and the results were fabulous. I was no longer messing around with manually adjusting my white balance, trying to get the "right" balance between several different color temperatures in use lighting up my layout room.
Since my layout is portable and I attend several shows per year with it, the new "daylight" module lighting attracts a lot of positive comments from onlookers, and when I'm set up in an arena with large windows, it is pretty amazing to compare the quality of light coming through the windows as nearly equal to the 5000K lights over my modules!
I still have warm incandescents in my living room, bedroom, den, etc., but now I light my workshop with 5000K lighting as well as my layout room. I really like the fact that what I build and paint on my bench looks the same on my layout now.
My suggestion is, no matter what style of light emitter you decide to go with, go with 5,000K for your daylight color temp. If I had lighting valences over my layout instead of drafting lamps, I'd go with 25W 5,000K CF fixtures every two to three feet 14" above your track, with the inside of the valence painted with the equivalent of Titanium White, or gluing crinkled aluminum foil on the inside of the valence to reflect and disperse the light.
By the way, my layout room is 11' X 25'...about the same size as yours.
Here's a photo of our modules set up at the Evanston Roundhouse Festival at the beginning of August of this year. Notice the color of the outside light coming through the open service door, the color of the layout lighting, and the yellow color of the overhead lights. This graphically shows how true 5,000K lights are to actual daylight.
(https://lh5.googleusercontent.com/-jxaO0YPDVKQ/UEGEaN93HqI/AAAAAAAAAsc/g7OzZNJJcUo/s800/_DSC7715.JPG)
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More important than the color temperature you choose is consistency. My recommendation would be to choose a color, and then change out the lighting for the entire space to match (as well as provide the ability to completely block any windows). This means no matter where or how you photograph your layout, you won't have to work very hard--if at all--to achieve correct white balance.
One concern I have with "daylight" temerature lighting is the UV component. If you use fluorescent lamps, be sure to get UV filters for them to minimize fade damage to the layout. Personally, I like the warmth of the tungsten temperature range, as it simulates the "sweet light" of late afternoon, which I also find easier on the eyes. The thing I find remarkable about some of the better warm white LED lamps is how close to tungsten they fall in temperature; I've been able to set my camera to the factory tungsten setting, with no need to tweak the resulting images any further.
I'm not overly fond of compact fluorescent lighting. For one thing, I've found too often the lamp life to be shorter than what's claimed. They also have a warm-up period, during which their brightness changes considerably, and their color temperature shifts somewhat, which forces you to wait until they're all at full operating temperature before you can do any critical photography. Plus they're often fussy about being dimmed; even those advertised as dimmable often flicker when dimmed, or dim a token amount before shutting off. Consequently I've replaced all of the CF lamps in my home with LED fixtures.
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Like DKS, I am not overly fond of CFL's either. They have their shortcomings, but...they also have their advantages and after weighing both the advantages and disadvantages, several of my N-scale modular associates (and me) have chosen them.
As per DKS's comments about their shortcomings, it is true that they take a while to "warm up" to their proper operating temperature and become consistent (at least to my eye). However, it's not hours, but from 1 to 3 minutes...so I'm usually turning on the DCC, or putting things on the track or composing my photo while that's going on. I don't find it to be an inconvenience.
I was not aware of any UV problems with the 5,000K lights, as they are not listed as "grow" lights. They do emit a small amount of UV light (all of them, no matter what color temperature) unless they are "double glass" CFL's, then the problem goes away with the second layer of glass acting as a UV filter. I will be replacing mine with double glass CFL's.
I am however, aware of the UV problems with quartz-halogen lights (that's why they have thick UV filters on the lamps).
Since I do not dim my lights for night effects (as DKS does) dimming is not something I take into account and I have had no experience with dimmable CFL's.
CFL's, if they are turned on and off a lot, do not last nearly as long as advertised. However, in the two years I've had my CFL's in use on my layout, I have yet to have one cease to function. Maybe that's because when I turn them on, I am usually going to work on the layout for several hours.
Since my modules are portable, an important quality of CFL's is their low power consumption (approximately 1/4 that of incandescents). Used to be that the big extension cords would get warm when all the 100W lights on the club modular layout were turned on. Now, they stay nice and room temperature.
Another quality that is important for portable layouts is that CFL's will take rough handling (meaning jiggling during transportation) better than will incandescent bulbs. Sometimes in the past, I've had two or three incandescents "die" during transportation to a show...that's why I'd always carry extras with me. However, I have not had similar problems in the past two years with my CFL's.
Although I would prefer LED's, their cost vs light output is prohibitive for me. I get a lot of lumens for my buck with CFL's.
As to color temp, it's a matter of personal taste. However, the "golden moment" photographers love so much (myself included) does not only involve the warming of the color temp of sunlight as it filters through the atmosphere, but importantly, also the angle of the light source. A very vertical position of "golden" light looks odd to me...like sunlight at noon filtering through clouds of smoke generated by a nearby wildfire.
To my eye, evening lighting also involves long shadows such as those in this photo, taken a long time ago using Fujichrome Velvia, a Nikon F2 with a 60mm Nikkor Micro lens with quartz-halogen lamps providing the warm, angled light, and me "painting" the skyboards with a 5,000K flood during the long exposure...because, even in the evening, the sky stays blue, even though the clouds may "warm up".
(https://lh5.googleusercontent.com/-3hizw1Z4Xnk/UECGa4IxvbI/AAAAAAAAADk/euUnGOxaRFA/s800/Evening%2520F%2520Units001corrected.jpg)
The printing industry standard for evaluating and judging color is 5000K (daylight), and "light booths" are commonly in use throughout the printing industry to properly judge both the consistency and quality of prints coming out of the presses. Since I was involved in the printing industry for 18 years (part owner of a press) my experience, of course, leads me to prefer 5,000K lights.
As a long-time pro photographer, my recent experience with being able to fiddle with the white balance of my digital photos, either post-camera (using Photoshop) or in-camera (using camera controls) without having to screw on a warming or cooling filter, :D has told me that if I want warmer lighting for my photos, I can easily manipulate the quality of color in my photos by simply setting my white balance to either "shade" or "cloudy" which will warm things up considerably. However, I usually prefer to do my processing post-camera on my calibrated monitor using Photoshop, masking, cloning and generally having fun with my photos. I have found that if the quality of light is poor, which usually means different color temperatures of light illuminating a scene (incandescents, fluorescents, halogens, the window...all at the same time), the quality of color in my photos is not "complete" (meaning the full spectrum of color is not available across the whole image). Excessively "warm" or "green" lighting (normal incandescent or traditional fluorescent lighting) actually eliminates certain visible colors when either being perceived by the human eye, or recorded by a camera.
The point is, if you're going to take a lot of photos of your layout, use lighting that contains the complete ROYGBIV spectrum (5,000K daylight) which can then be manipulated for whatever effect you're shooting for (either cool or warm) because the whole visible spectrum is there to play with. If you want consistent lighting that pleases only your eye, then go with whatever you like, since no two human eyeballs/brains perceive color exactly the same. You might as well use what "tastes" best to you, rather than use what functions best for your camera due to the engineered-in calibrations of its sensor and software.
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I've followed this thread with interest. I have been attracted to LEDs as a light source and I am learning quite a bit from some of the posts here. I'm skeptical of the quality that reels purchased on ebay might provide, but it is an attractive way to do valence or lower level lighting for a layout.
One comment I'll add is that people seem to have a lot of lights for their layouts. I guess I am rather concerned about issues like power consumption, but when I finished the layout room (approximately 10' X 10'), I installed two circuits of pot lights and installed 14W warm white CFL spot lights. The dual circuit allows only turning on two lights for quick trips into the room. The brand I bought turned out to have a very noticable warm up period, but like Bob, I don't see this as much of an issue. The bulbs have worked fine for 6 years and I expect probably 4-6 years more, given most of my CFLs have lasted ten or more years (we have one from 1993 that still operates). The total load is under 60W, and it is quite bright in the room with this. It seems excessive to me to have more lighting and I think the heat load would be substantial, even with CFL or tube versions. In Alaska, heat load might be a benefit, but in many places this is a concern.
The CFL and tube technology is quite mature now, which means a good variety of products, generally good quality, and excellent energy/light output performance. Judging by a survey at Home Depot today, I see CFLs are about 1/4 of the price of the same lumens from LEDs. There are conservation coupons at HD today that made my four-bulb purchase total $3. Given this, I would seriously consider tube or CFL options where you have space or if you are thinking about general lighting of the room.
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The point is, if you're going to take a lot of photos of your layout, use lighting that contains the complete ROYGBIV spectrum (5,000K daylight) which can then be manipulated for whatever effect you're shooting for (either cool or warm) because the whole visible spectrum is there to play with.
Except for ordinary tungsten lamps (and even they have a trace of near-UV), all light sources contain the complete spectrum; it's just a matter of where it peaks that creates its apparent color temperature. For that matter, fluorescent lamps are more problematic than tungsten sources since they contain spikes in their spectra which can affect color rendition, whereas tungsten has a very smooth output curve. Very costly full-spectrum fluorescent lamps will be more controlled than what you'll find at the big box stores, but they will drain your wallet. Thankfully, modern cameras and software are able to compensate--to a degree; they're not all perfect.
I will say that the early LEDs were wimpy and had color issues. They are, however, improving very rapidly, and the latest ones are quite powerful and seem to have a very servicable spectrum. (I'd love to run a spectral analysis of them--if only I had the gear.) I use them now for product photography and I have no complaints.
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I'm surprised that the lamp's CRI (Color Rendering Index) has not yet been discussed in this thread. For explanation see http://en.wikipedia.org/wiki/Color_rendering_index (http://en.wikipedia.org/wiki/Color_rendering_index) This is very important with any sort of fluorescent and LED lights. DKS' explanation of the "peaks" and color temperature is IMO a bit awkward but it is not incorrect. However, besides the color temperature, the CRI is also important for true reproduction of the full range of colors visible to the human eye.
Most white LEDs are actually blue LEDs where the actual light emitting element is placed under a dome of phosphor (or the LED case is molded of epoxy/phosphor mixture. WHen the LED is emitting light, some of the blue light passes through the phosphor layer while the rest of the blue light is converted to other colors (green , red and colors in between) by the phosphor. The CRI of white LEDs depends on how ell the phosphor covers the visible spectrum of light.
Fluorescent tubes (including CFLs) work on a similar principle. The ionized gas within the tube emits UV light and the phosphor coating on the inside of the glass tube converts the UV light to visible spectrum. Again, the CRI depends on the type of phosphor used.
A simple visual demonstration can be rigged by covering the light source with a piece of cardboard with a small home in it. A good prism substitute is the surface of a ordinary music CD or a pressed (not burned) data CD. Place the light source with the cardboard apperture in a dark room and view the light emitted through the aperture reflected of the surface of the CD. That will show the spectrum of light emitted by the light source.
Most current white LEDs have fairly complete light output over the visible light spectrum. Most fluorescent lights notoriously have very distinctive bands of emitted color, with dark bands in between them. Those usually have a poor CRI. As a result, when using them for illumination, they can change apparent colors of objects.
The best way to make sure to get lights which will show true colors is to find out their CRI values. I prefer using lamps with CRI value of at least 85.
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This is a very interesting thread. I decided to Google about to see what the dif was between actual sunlight, incandescents, LEDs and CFLs as far as their Color Rendering Index (CRI), Spectral Power Distribution curves, and "perception of quality of light" by humans. I discovered this article by Popular Mechanics that showed graphically the difference in the way different light technologies render their colors...or perceived colors. Go here: http://www.popularmechanics.com/technology/gadgets/tests/incandescent-vs-compact-fluorescent-vs-led-ultimate-light-bulb-test-9#slide-1
When it's all said and done, I'm not sure what any of it proves other than go with what you like! Each light source has its advantages and disadvantages, but the clear loser is the incandescent, especially considering the governmental obsolescence being imposed upon them, the heat they generate and their obvious inefficiency. However, their CRI and SPD curves are smoothest, whereas both LED's and especially fluorescents have "spikes" and "troughs" which means the color temperatures of both of these technologies are "correlated" or "averaged" temperatures, and because of the sharp spikes and large troughs, their CRI's are correspondingly lower than incandescents or true sunlight.
Which means, for me, that the very best technology for taking photos would be incandescents...but...I am not going back to them because of their heat, short life, obsolescence and power consumption.
Second best would be LED's, but the price per lumen is too steep. Interestingly, even though their SPD curves are smoother than CFL's, the perception of humans on them was more mixed. I'm sure it's the "delivery" system, or the optics needed to get them to be more similar to incandescents. I am sure as the technology matures, that will be worked out and the price will come down.
As far as Peteski's comments about CRI...I am not sure how a person would find out what the CRI for a particular light source is, since the rendering of the color of light between manufacturers is notoriously inconsistent. That means each manufacturer would have to post the CRI of a particular LED "bulb" or CFL somewhere (website?) and allow the consumer to pick which light source they prefer...cheap and low CFL, or more expensive and better CRI.
Since you (Peteski) buy lamps that have a CRI of 85 or above, how/where do you find it? Or, do you test each batch of bulbs you purchase?
Yep DKS, the total visible spectrum IS present on all lamps, but...CFL's do have big troughs, no matter what their color temp, and I am now certain that my contention that 5,000K CFL's have more of it is incorrect.
However, I am not certain what effect a low CRI would have on photography, since digital photography is becoming extremely competent...especially in the more professional-leaning DSLR's. Guess I'll just keep doing what I'm doing, since that seems to work pretty well for me and my Nikons!
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I completely agree that the best advice about choosing the spectrum of your lighting is to try it in as-close-to-layout conditions as you can and see if you like it. You should especially gather locos and cars of different colors and see how they look to you. When I first tried my daylight bulbs, I was quite surprised how vivid all the blues were, for example. Effective temperature and CRI are just two numbers that attempt to characterize what is typically a very "rich" spectrum. By the way, CRI values are often listed on the box for fluorescent tubes; I imagine the same is true for CFL's and LED's, but I haven't researched that.
For those of you interested, I thought I'd mention a little of the background physics. My apologies if it's pompous, or if graphs give you a headache. Please skip it in that case. The first thing to ask is: what is the spectrum of sunlight? This Wikipedia plot of brightness vs. wavelength summarizes the that information pretty well:
(http://upload.wikimedia.org/wikipedia/commons/4/4c/Solar_Spectrum.png)
The smooth curve labelled '5250 C Blackbody Spectrum' is the spectrum that would be emitted by a perfectly absorbing ("black") body at a physical temperature of 5250 Centigrade. The shape of this spectrum is governed by quantum statistical mechanics and was first predicted by Max Planck near the turn of the 20th century. In fact, Planck's explanation of this spectrum invoked the idea that light consisted of quantized particles ("photons") rather than continuous waves, and was one of the first lines of reasoning that led to the quantum revolution in the following decades. It was a remarkable intellectual triumph!
The surface of the Sun matches the blackbody conditions pretty well. (Of course the Sun is not "black", the term means that any light the reaches the Sun would be absorbed, or "thermalized", by the hot gas of its atmosphere, and eventually re-emitted with this spectrum.) The actual spectrum of sunlight measured in space is shown by the yellow curve. While there are a number of fine absorption lines in the solar spectrum, the overwhelming character of it is it smoothness and its peak at a wavelength of ~550 nm (greenish-yellow light). Once sunlight reaches the atmosphere, a good deal of it is absorbed or scattered by atmospheric gases. A typical spectrum measured on the ground looks like the red curve above, but this will depend on time of day, particulate content, and elevation. In the visible range (~390-750 nm), the spectrum mostly just looks like a dimmer version of the primary spectrum.
The effective temperature of an artificial light is an attempt to identify which blackbody curve is closest to the actual spectrum produced by the lamp. To see what this means, it helps to see how the blackbody spectra change as you change the temperature of the emitter:
(http://upload.wikimedia.org/wikipedia/commons/thumb/a/a2/Wiens_law.svg/648px-Wiens_law.svg.png)
The peak of the spectrum shifts to longer wavelengths as the temperature decreases. This is a direct result of the fact that photon energy is proportional to its frequency, nu, specifically, E= h*nu, where h is (appropriately enough) Planck's constant. As the temperature drops, there is not enough energy in the system to populate the high energy (high frequency) modes, so the high frequency side of the spectrum rolls off more and more, which means less blue, more red. If you have a lamp with a measured spectrum, you can mathematically 'fit' a blackbody spectrum to it and find which one it most resembles; that is the effective temperature (or 'correlated color temperature') of the lamp.
As noted earlier, a fluorescent lamp typically has a feature-rich spectrum, something like this:
(http://upload.wikimedia.org/wikipedia/commons/thumb/e/e6/Fluorescent_lighting_spectrum_peaks_labelled.gif/800px-Fluorescent_lighting_spectrum_peaks_labelled.gif)
Describing this spectrum by a blackbody curve (and temperature) is a crude approximation at best, but it is well-defined, and it does give a surprisingly good indication of what the light looks like to a human. (Part of the reason for this is that the human eye responds logarithmically, so that we can cope with a large dynamic range of light. This has the side effect that features in a spectrum tend to be de-emphasized by the eye.) Roughly speaking, the color render index is a measure of how much structure is left in the spectrum after the best-fit blackbody portion is subtracted from it. It is defined as 100 if the spectrum is already a blackbody, and the values drop from 100 as more and more structure remains in the subtracted spectrum. The index tells you very little about the nature of the structure (e.g., which wavelengths are enhanced or diminished), and the actual recipe for measuring CRI is rather technical.
In a digital camera, the CCD sensor is typically divided into separate red, green, and blue pixels, in a Bayer pattern:
(http://upload.wikimedia.org/wikipedia/commons/thumb/3/37/Bayer_pattern_on_sensor.svg/700px-Bayer_pattern_on_sensor.svg.png)
The R, G, and B filters are broad and centered on their respective colors. The only thing that matters to a camera is how each of the three filters responds to the spectrum presented to it. The goal of color correction is to adjust the relative RGB response to what it would be if the camera were presented a 5000 K blackbody spectrum. As long as each R, G, and B sensor detects some light, color correction is possible, though it can get tricky in practice.
Sorry to ramble... I love physics.
-gfh
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Gary,
Who let the rocket scientist in? ;)
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Outstanding Gary! This has to be a Railwire first: The on topic presentation of the Planck curve and Wien's displacement law. I appreciate the figures being presented as wavelength instead of frequency as you physicists are apt to do! I haven't been so happy with a post since Dave Vollmer posted a geologic map in his building thread. I wish I still had access to a visible wavelength spectrometer, but I now work in the thermal infrared and microwave region of the spectrum. The fluorescent light spectrum is a very useful figure. Interesting how little blue (450-495 nm) there is in this spectrum compared to green (495-570 nm) and red (620-750 nm). Thanks for digging that up.
This has been a very interesting discussion and I have learned quite a bit. In the end, like all things it comes down to tradeoffs. Incandescent lights are out for me due to heat and power requirements. As Robert points out, there are times when they have their place, but not for lighting the entire railroad. I have decided to stay away from LED light strips at present, but may pick up some shorter lengths for testing. The LED fixtures mentioned by DKS look great, but I am still hesitant to do that way at present (worried about valance construction). My plan at present is to experiment with T-8 fluorescent tubes, augmented by some CFLs were needed. The UV warning is really appreciated. I really appreciate all of the input and encourage others to weigh in.
Best wishes, Dave
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You guys are a bunch of nerds. :D
As opposed to those of us who just play with toy trains. 8)
Jim
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Gary is a nerd who plays with trains! 8) Seriously though, Gary, that was an excellent explanation!
Bob, I read your other post in the Crew Lounge and I'm surprised that you (as a serious photographer) were no aware of the CRI specifications for lamps. I'm not trying to put you down, I'm just surprised, period. I'm an amateur photographer and I have been aware of CRI lamp ratings for several years.
As gary eloquently explained, Digital cameras use sensor elements which use RGB filters over the light detectors. As he also explained, the high CRI rating od a lamp doesn't guarantee a good performance with a digital camera. If the high-CRI rated lamp has color peaks in between the colors used in the camera's sensor, this will results with poor color rendition. My logic dictates to me that the best illumination for a digital camera would be a white lamp in which the emissions peak at red, green and blue (at the same wavelengths as the camera sensor's filters).
Such pairing of light emitter/detectors exists in flatbed scanners which use cold-cathode fluorescent lamps and light sensors with red, green and blue filters. Those lamps are designed with specially blended tri-phosphor coating. They appear white to the human eye, but when the light is viewed split through a prism (or reflected off a CD) they clearly show that they are emitting red, green and blue light and nothing in between those colors.
As far as finding CRI rating of lamps, more and more often manufacturers include this raring either on the packaging or in online technical specs.
The Wikipedia article about CRI to which I linked in my last post shows a photo of such package.
(http://upload.wikimedia.org/wikipedia/commons/thumb/5/58/AmbientLED.png/433px-AmbientLED.png)
Also, PHILIPS fluorescent tubes I buy (at Home Depot) have CRI specified on them. For example one of the bulbs I use is "Soft White", COlor temperature 3000K, CRI=85.
Here is a chart of fluorescent lamp specs, including CRI (although it is very dated)!
http://www.thekrib.com/Lights/fluorescent-table.html (http://www.thekrib.com/Lights/fluorescent-table.html)
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Gary is a nerd who plays with trains! 8) Seriously though, Gary, that was an excellent explanation!
Guilty as charged! Thanks for the kind words though. Having spent some time with Dave in Anchorage this summer, I knew he did remote sensing, and your post on CRI made we want to fill in a bit of the back story. So I thought I'd have a little fun with it, and thought Dave would get a kick out of it.
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Thanks Gary. I really did enjoyed your post. The plot of the solar spectrum also explains why we see light in the 450-750 nm region...because that is where it peaks.
Best wishes, Dave
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WOW! Love this thread! Although light behaves as both particle and wave (until observed), a fact that Schroedinger admitted, but made fun of, modern technology uses this fact and many more in the quantum mechanical toolbox without explaining the "why" of it all...an obvious omission that engineers and practical physicists hardly worry about when designing machines to use these principles for our enjoyment and benefit.
Gary...no way would I consider your explanations "pompous". The graphs and charts make what your explaining much clearer.
Peteski...I'm not offended whatsoever by your curiosity as to why I've never heard of CRI before. Actually, I'm a little curious as to why I haven't heard of it too. It has not been a serious omission in my photographic efforts, as I am pretty happy with my results. When I think about it, it's probably because I use professional lighting equipment, and available light...both of which I trust to give me consistent results.
It's only recently that I've been using my layout lighting as my primary lighting source for my model train photos (like in the last two years).
In all my university photographic classes and on-the-job apprenticeships over the years, not once have I heard anything about a lamp's CRI as something I needed to worry about as far as photographic quality is concerned. When I wanted a lamp to replicate daylight, I'd just buy them at my local photography store...250W incandescents of course...and they'd last about six hours. I had half a dozen of 'em for my copy table before I started using strobes.
Of course, nobody used fluorescents in those days (we all avoided them if at all possible because they were impossible to filter for), and nobody had heard of LED's powerful enough to be used for photography.
I guess it's kinda like an artist not knowing the composition of his pencil "lead" when he's drawing a portrait...just how it feels in his hand and looks on the board.
Guess my age is showing... :D
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Some other thoughts on this:
About a year ago, I was remodeling some rooms in my house and wanted to use recessed lighting with LED bulbs to avoid heat issues. That is the neat thing about LEDs: they are cool to the touch even after hours of operation.
I used EcoSmart and another brand that I can't recall (Commercial Electric?). I ended up keeping the EcoSmarts, despite a very cool color (that is a little too blue for my tastes) and a .5-1 sec. turn on delay (annoying since I have 4 in one room). The other brand needed to be grounded (which I thought was odd) and 1/2 of them worked out of the packaging. I returned them for Philips.
The Philips LED bulbs are perfect - great color that is consistent with the label on the packaging. The two that I have turn on at the same time. However, they cost a little more.
If I was doing layout lighting, I would select a flexible track lighting fixture and populate it with these $29 bulbs (http://www.homedepot.com/Philips/h_d1/N-25ecodZ5yc1vZ15bZ12kz/R-203321686/h_d2/ProductDisplay?catalogId=10053&langId=-1&keyword=led+light+bulbs&storeId=10051#.UHbJ8o6hBHg) (HD also sells a 4 pack for $107). I bet the four pack would be sufficient to light 12' of a layout.
Just my thoughts.
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About three years ago, I started investigating LED lighting for the layout. The thing that caught my attention was the flexible LED strips with 3 LEDs per 2" segment that could be cut into segments that were a multiple of 2" that would allow the strips to be bent in the "horizontal" plane rather than the "vertical" one. These operate from a 12VDC source and the equivalent of a Pulse Width Modulated transistor throttle allows complete control for dimming. The strips I experimented with have a colour temperature of 3500 K and were augmented by 12 VDC LED floodlights with a colour temperature of 4100 K.
(http://www.trainboard.com/railimages/data/500/LED_Lighting_Test_-_1.jpg)
The photograph shows the test area on my under construction layout. In the foreground-background direction, the strip LEDs have a 120 degree illumination angle so the strips are mounted at a 45 degree angle behind a valance that mimics the shape of the front fascia (when it is installed). A contoured horizontal baffle will restrict the light to the actual scenicked surface of the layout with little or no spill-over into the aisles. As noted on the photograph, the illuminance of this combination at the centre of the scene, as measured by a Gossen Luna 6 Pro light meter in incident (rather than reflected) mode, is approximately 550 - 600 lux. A brightly lit office is typically 1000 lux. To my eye, the colours in the photograph are a good match to what I see on the layout and are also close to what I see at the workbench. If I wanted to increase the brightness and broaden the spectral range of the lighting, I would consider adding a second strip of LEDs with a colour temperature of 2700 K. However, with the room lights turned off, I am happy with the illuminance of the current set-up.
(Edit: The only illumination for the photograph was from the LEDs. The room lights were turned off.)
At the time I started the experiment, the LED strips were costing $15/foot! The same strips are now down below the $1/foot range. The LED floods use an MR16 socket and run in the $9 range each. These are Canadian prices. My plan is to use one of the floods every 2 feet. Based on the experiment, I expect to illuminate both decks of a 15' X 17' L-shaped layout with a total power consumption of about 200 W. In terms of room heating, this is roughly equivalent to having two extra people in the room during an operating session.
Cheers,
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Interesting read about LED life http://hackaday.com/2012/10/23/graphing-the-efficiencies-of-led-light-strips/
Also I wouldn't think about LED lighting with those "strips", use these as a minimum
http://www.luxeonstar.com/Neutral-White-CoolBase-Rebel-Stars-s/347.htm
These get pretty expensive for units with all the electronics and hardware to run them.
https://www.sparkfun.com/products/8202
http://www.ledwholesalers.com/store/index.php?act=viewProd&productId=746
Anyone try those 68watt fluorescent / 300watt incandescent equivalent bulbs? I have one, its huge but I've only seen them at 2700K. I got one at HD for around $17.
Also off topic, I use 23watt/100watt equv. around the house and try to always dremel out holes/slots in the base to extend the lifespan. Only because I read somewhere they expire early from circuitry heat related failure (and from short powered on state cycles). Most of the CFL's aren't mounted with the base down anyway, so they get hot.
And no I haven't done any testing to back this up with solid data, I've planned to but forget when changing bulbs.
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There is a thread on the MRH forum going right now (I feel like I just admitted cheating on my wife :trollface:) that is quite good at addressing the LED subject... specifically the strips found on eBay from Hong Kong.
http://model-railroad-hobbyist.com/node/9736