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Thread: UV light source thoughts

  1. #1

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    Oct 2003
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    UV light source thoughts

    I just reread Sandy's very well written article on unblinking eye about UV light sources. I have a question followed by a rather lengthy explanation behind the formation of the question, please bear with me.

    Sandy

    I noticed that the HID lighting set up you illustrated was positioned with the bulb in the verticle position. And you talk about the light quickly falling off at the edges. You placed the light 20 inches from the surface in order to cover, I think it was 11x14. Are you aware that there is a difference in HID bulb mounting? There are those that were designed to be screwed into your lightsource in a verticle position and there are those that are meant to be mounted horizontally? If you were, did you try both? and if you did, did you notice any difference in the evenness of illumination?

    In the field of hydroponics it has been known for a long time that the horizontally mounted bulb is much more efficient because it provides a much more even illumination over the garden area. In my classroom I run two horizontally mounted 1000watt fixtures. One is a Metal Halide and the other is an AgroSun bulb designed to mimic sunlight. The illumination of these two bulbs are very even. If you are still running the HID unit you might want to expore the horizontal mount, though you would need to replace the reflector. I have Tested a verticle lamp on my gardens and found it to have a serious hot spot with quick light fall off. I do not have that problem at all with the horizontally mounted bulbs.

    I must say that your article was very well written and this thought popped in my head.

  2. #2

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    UV light source thoughts

    Mark,

    Thanks for your interesting comments about my article on UV light sources.

    I am aware of the advantages in terms of eveness of illumination of horixontally mounted HID lamps. You can appreciate this by looking at any of the graphic arts printers from NuArc or Olec. All of them have horizontally mounted lamps.

    However, when I wote the article to which your refer one of my primary objectives was to provide an inexpensive HID alternative to a bank of UV fluorescents. The Luminaire unit that I describe in the article is inexpensive, available locally at good electrical supply stores almost anywhere in the US, and easy to set up. In this sense this type of light take less time and trouble to assemble and set up than a bank of UV fluoresents, and that was the point I tried to make in the article.

    There are clearly more efficent exposure systems out there and I would be very appreciative if you would forward me further information about your UV exposure system, which I presume is based on horizontally mounted HID bulbs.
    For discussion and information about carbon transfer please visit the carbon group at groups.io
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  3. #3

    UV light source thoughts

    Mark,

    This is really an issue of optics, and has little to do with the actual lamp orientation, although the orientation does affect the distribution of the light from the fixture.

    What I mean is: It is possible to design a vertically oriented luminaire to provide a uniform light distribution on a surface, as it is also possible to do the same with a horizontally oriented lamp. However, given the particular geometries of the situation, it is likely that one orientation or the other will make the optical arrangements necessary to achieve the desired distribution a bit easier.

    There are numerous practical reasons for the orientation of a lamp in a luminaire also, as is apparent when you consider the luminaire that Sandy has in his article (called a 'high-bay' or 'low-bay' luminaire, depending on the spread of light delivered).

    This luminaire was designed to hang from the ceiling of a relatively high open space, and provide relatively uniform illumination on a work surface that is typically 20' or so below. The light distribution from the fixture is intended to by symmetric, because these luminaires are often laid out in a grid. By placing the lamp vertically, the majority of the light leaving the lamp will be redirected by the reflector into a desirable distribution, resulting in little uncontrolled light. Also, keeping the lamp vertical makes the luminaire easier to keep properly balanced, which keeps the luminaire hanging plumb.

    However, it is unreasonable to presume that when you measure uniformity at 20" there will be no falloff, because the luminaire was not designed for this application. Sandy's method to even out the exposure is a reasonable approach to correct an inexpensive, off the shelf luminaire so that it provides reasonable distribution for exposure purposes.

    I believe the light from the luminaire is actually crossing somewhere in the path, as that is typically how a high bay luminaire is designed. If this is the case, it will result in a substantial nonuniformity until the beams of light have completed crossing, which may be many feet below the luminaire.

    A horizontally-oriented lamp has some benefits. If you place a bare lamp over a surface, it effectively acts as a point source, with light falloff following the square to the distance rules. Even unmodified, a point light source does a reasonable job WRT uniformity as long as the source is a reasonable distance away from the subject plane. Simple geometry calculations will determine if the distance is suitable for the size of the subject.

    However, when a reflector is wrapped around a horizontally oriented lamp, the light can fairly easily be made much more uniform, because the upward originating light can be redirected to help cancel out the inherent falloff associated with the point source nature of the downward originating light. This is exactly how most of the graphic arts light sources are designed, and they work quite well for that application.

    The reflectors have to be designed for a very specific subject distance, however, or they will either overcompensate, or undercompensate.

    This is all a long winded way to help explain that the optics for a particular luminaire are designed for a specific lamp orientation, and for a specific purpose and subject distance. It would be wholly unsuitable for a horizontally orientated lamp to be placed in a high bay fixture (even if it could fit), because the optics were designed for the vertical orientation.

    Fixtures that are designed for low mounting heights, like hydroponics luminaires, probably do use a horizontally oriented lamp because of the angles involved in the coverage, however, they are not inexpensively available at the local Home Deopt for purchase, which I think was a primary requirement of Sandy's article.

    If a person were intending to spend some substantial money on a specialized luminaire, then the logical approach is to purchase a used plate burner, since they have a built in vaccuum frame and an integrator. They can be obtained from Ebay for anywhere from $300 to $600, and are substantially more convienant than any home-built approach that I have used. They are also much a more energy efficient solution, since the light is turned off between exposures.

    ---Michael

  4. #4

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    UV light source thoughts

    Sandy

    My "UV exposure system" is really a 5x15 foot indoor hydroponic garden(education grants are cool) that I will use as light sources on those few cloudy days we have here in AZ.

    One of my lights, the non-"professional" set up, was put together to show how to set up on a small budget. Bulb, Ballast, mount, and reflector(diamond Luminarc horizontal mount reflector) cost under 200 dollars with a majority of the money going for the reflector. It gets the same results as the 500 dollar setup from HydroFarm.

    In your Article you talk about the fact that you need to wait for the light to heat up, which is definately true. Do the lights in the plate burners need to warm up?

  5. #5

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    UV light source thoughts

    Mark,

    You have an interesting set-up. No many of us have units that will cover 5X15 feet!

    The bulbs in plate burners also have to warm up before they reach peak output but they do so fairly quickly. The metal halide bulb in a NuArc 26 1K takes about 20-30 seconds to reach full output whereas the metal halide bulb that fits the Luminaire type reflector takes between two and three minutes. In general metal halide bulbs reach full ouput much faster than mercury vapor bulbs and they are generally interchangeable iin the same fixture.
    For discussion and information about carbon transfer please visit the carbon group at groups.io
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  6. #6

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    UV light source thoughts

    Mark,

    Designs, material lists, sources would be a nice addition to the description you gave of your setup. Winter is coming, the fog is rolling in here in South San Fransico Bay area. All those days of clear blue skys are going away.

    Thanks for any help,

    tim

  7. #7

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    Oct 2003
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    UV light source thoughts

    Sandy and Tim.

    I actually have more light than I need with two 1000watt units. One unit moves on a six foot lite rail light mover that is how I get to the 15 feet of coverage. The lite if not moving would cook my veggies in a 5x5 area of pretty even illumination The pamphlet says it will cover an area of 8x8 at four feet from the plants, but the light fall off is noticeable after about 6 feet.

    Hmmm......Every one I talked to about lights said there was a diffeent ballast needed when moving from MH to HPS or spending a lot on a convertable ballast. One company said with a metal halide ballast the sodium lamp would not burn as efficiently. Maybe I was being had, I do not know but the sickly yellow light in a 6th grade classroom would be quite depressing so i had no desire to get one.

    Everything I got for my garden is from a small store in Albuquerque, called AHL- http://www.ahlgrows.com/?ahlhydroponic

    I bought a Hydrofarm radiant 1000watt system from them for about 320ish and the agrosun bulb for about 120more. I also got a Diamond Lumenarc horizontal reflector for I think 60 dollars but it was on sale and it is not on their website or in their newest catalog. Might be there I just did not look real hard Other places have it I am sure. Try typing it in a search engine or if you are in a city just call a hydroponic supply store. The bulb was bought off Ebay from seller a813335. It was cheap I can't remember exactly how much. And the ballast came used from an online add for 100 dollars. While I in no way advocate the growing of illicit green leafy plants, the growers are very budget minded and often have used stuff like this for sale. Considering the smell surrounding my ballast when I unpacked it, it has a much more legal home now.

    I was going to just buy a cheap reflector but the hydroponics people at the University of Arizona explained the importance to a really well designed reflector. The diamond lumenarc has twelve reflective surfaces engineered to focus light from twelve different directions onto the garden surface. Both lights are designed to be suspended four feet above the garden. I am not sure if the diferent light angles are as impotant in a UV source but it really peps up the basil and lettuce.

    I do not know how to post a plan of the set up on this site. If you can tell me how I will. I am only going to be using the area for four seperate growing systems so I will have enough room to pull a student desk over to print on if I get this whole thing going like I want to.

    Hope this is the information you wanted.

  8. #8

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    UV light source thoughts

    Mark,

    That was great. Enough information to get started and the plans in the end should be pretty self explanitory. I live in SJ, CA and we have a hydroponic store or two around here. I'll check them out as well as your references.

    Thanks a lot,

    tim in san jose

  9. #9

    UV light source thoughts

    Tim and Mark,

    I would caution that a light designed to cover a 5 foot wide zone may make a terribly inefficient and slow printing light source if you are intending to expose an image that is at most about 2 feet wide.

    The speed of the printing is related to the amount of incident UV and near-UV light on the printing easel. If you take 1000w of MH light and spread it over a 5x5 foot area, it is covering 25 square feet. If the same lamp were used, but the light concentrated on a 2x2 foot area, then the coverage will be 4 square feet. The larger coverage yields more than a 2 1/2 stop reduction in light, which will result in a substantially longer printing time.

    The hydroponics lights may be suitable for the task desired, which in this case is typically a small target zone with a very high level of uniformity, but I would suggest you check it carefully before you commit the time to set up a printer based on these lights.

    ---Michael

  10. #10

    UV light source thoughts

    I thinking of trying a facial solarium myself -for contact printing on 8x10 Azo. Time to hit the Goodwill stores.

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