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Improving CF bulbs for task and shop lighting

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  • Improving CF bulbs for task and shop lighting

    I used compact fluorescent bulbs for the headlights on my lawn tractor. To make it work I designed a simple reflector that concentrates as much light as possible to make a flood light. I did this because the ready made CF flood lights suck. They have a diffuser and are always soft white, at least that is all I can find. They also don't perform half as well as my design.

    With a simple reflector a CF bulb can provide twice as much light or more where it is needed. It isn't a spot light but a flood light with very even distribution and no hot spot. I realize that for many this is a very simple project but not everyone has experience with even simple sheet metal work.

    The reflectors are made of standard aluminum flashing which is then polished to a reflective finish. If you have a reasonably priced source of what is called "reflector sheet" then that would make an even better reflector. I checked around here and the only way to buy some is to order an entire 4 x 8 foot sheet at about $200. That's too rich for me so polishing aluminum flashing is how I do it. I will point out that even highly polished stainless steel makes a very poor reflector as the maximum reflectivity of SS is only around 50% while the reflector shown here is about 80 percent reflective.

    Below is a series of pictures. I will refer to the pics by number.

    In pic 1 are some 8.5" discs cut from standard 9" flashing by stacking up five to ten 9" squares and cutting them in a vertical band saw using a center pivot. Easy to do and a wood cutting blade works fine for this.

    Pic 2 shows the tools needed for polishing. I use one buffer wheel to apply Mother's Aluminum Polish. Then the second wheel is used to remove the residue. The disc is screwed down at the center so it doesn't turn into a Frisbee of death.

    3: About 5 minutes buffing gives a good reflective finish. Be careful not to catch the edge with the buffer turning toward the center of the disc. Always brush away from center.

    4: A method is needed to fasten the reflector in it's final shape. I find that the best and easiest solution is to make some bent clips from thin mild steel sheet, These clips should be prebent so that all that needs to be done is a final squeeze with some Visegrips.

    5: The polished reflector is marked for cutting the center hole for the CF bulb. A hole diameter of 2.5" is about right. You can use a compass or the cap of a rattle spray paint can is the right size. Cut out a pie shaped piece to give access to the center cut. This is where you can use that $5 set of aviation snips to cut.

    6: Warp the sheet around into a cone and press on a clip on the OD with the locking pliers, squishing it flat to hold the metal. The center hole should be made slightly smaller than the ballast OD of the lamp this is meant for. About 1/16" smaller is good. This is accomplished by varying the amount of overlap of the sheet metal. Add two more locking clips, one to the OD and one to the edge of the hole.

    7: Snip a series of 1/8" long cuts around the center hole. This makes it possible to press the reflector over the base of the bulb and stay in place.

    8: This is how it looks when installed over the base of the bulb. It should be positioned as close to the top as possible

    9: The finished reflector should look like this with the reflection of the coils of the bulb filling most area.

    10: This is a picture of a plain bulb (the left) and the same bulb with a reflector (right) as installed in a plain fixture in the unfinished ceiling of my basement. The images were taken with my Nikon 4300 in manual mode with all exposure settings locked and the flash enabled.

    11: On the left is the scene looking down the basement stairs with a plain bulb installed and warmed up. Exposure is locked at 1/60 second and f 2.8 with no flash. On the right is the same scene with the same settings but with the reflector bulb installed. Absolutely no processing except cropping and resizing has been used on these photos.

    As can be seen the reflector is very effective. This cannot be achieved by using an ordinary fixture with a normal shroud around the bulb even if it were as reflective. The distance and slope of the reflector won't be correct unless mounted as is shown here. By using the bulbs with such a reflector mounted the apparent brightness is approximately doubled which can either greatly improve task lighting in the shop or reduce the power consumption by requiring smaller bulbs. The reflector may even extend the life of the bulb somewhat by acting as a heat sink for the ballast unit which is where most of the heat is generated. It's also much cheaper than the equivalent CF bulb floodlight.

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  • #2
    I have never heard it called reflector sheet before, in the race car world it's called hi polished or mirror finished and yes it can be used as a mirror.
    Here in the midwest it's up to about 120.00 for a 4 x 10 sheet x .032.
    If you need any drops in the future holler at me because I go through ten to fifteen sheets a year and usually have quite a bit of small scrap lying around.
    Don't have any idea if it would be worth the freight.


    • #3
      That was pretty cleaver Evan. I had no idea that would make such a difference.


      • #4
        Reflector sheet aka Lighting sheet is a special product used mainly for lighting fixtures. It has a reflectivity of up to 98 percent and is made of specially optically coated aluminum.

        Hi polished aluminum is good enough but for maximum efficiency reflector sheet is the material to use. It's expensive.
        Last edited by Evan; 08-17-2007, 05:39 AM.
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        • #5
          Wonderful Post !


          The local home depot has a new kind of CF. It is suppose to have a light that looks just like sunlight. I got one and love it ! You can really tell a difference. There are also CF flood lights available IIRC. They are expensive though.
          Since I have a dozen or so of the old kind in the shop, I'll try out your method. I can always use the extra light. I tried this before, but did not polish the metal at all. And I did not make a cone, I just made a cylinder. Will try something like what you did.



          • #6
            How do those CF flood lamps compare with the old type has far as brightness?


            • #7
              Looked at link that's the same stuff I use, the suppliers up there are sure hosing
              you guys.


              • #8
                Looked at link that's the same stuff I use, the suppliers up there are sure hosing you guys.
                That's a very common problem here. I just priced out exchanging my acetylene B bottle and the cheapest I can find is $43. Keep in mind that the Canadian dollar is almost the same as the US dollar now so that works out to about $40 USD. The price in the US is around $12 to $15 for the same thing.
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                • #9
                  How do those CF flood lamps compare with the old type has far as brightness?
                  That depends on the type of CF bulb. There are a lot of cheap ones that don't work that well. I use NOMA Electric brand as they seem to be very reliable. Noma has been around since the 1920s.

                  Look at the lumens that the bulb is rated to produce. The cool white bulbs are more efficient than the soft white bulbs and are what I use. In general the CF bulbs are around 4 times more efficient so a 15 watt CF bulb is about equal to a 60 watt incandescent.
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                  • #10
                    Amazing difference! I have a couple of the CF floods, they have built in reflection so a backing would not help, but I think they are more concentrated than what you produced, good pics on "how too" Evan.


                    • #11
                      Originally posted by Evan
                      3: About 5 minutes buffing gives a good reflective finish. Be careful not to catch the edge with the buffer turning toward the center of the disc. Always brush away from center.


                      A wittle buffing Twick, (my best elmer fud impression)

                      I noticed buffing all around the edges of the aluminum where it meets the plywood and wanted to comment on a short cut I often take (if the "part" is uniform and will allow it, maybe you already tried and it wasnt, but you can always set it on top of a uniform spin plate underneath)
                      For grinding or buffing sometimes you can leave the center screw loose so the object rotates, then you start buffing for direct spin, once the object starts spinning then change the vector of the buffing wheel to control objects speed, Ideally you want a very slow but uniform object speed and while your buffer is kinda Crosshatching,,, very uniform and nice results, keep in mind the vector angle has to be changed as you go from center to outer, but it allows you just a small linear movement of the tool instead of covering the entire surface, you can also "cant" it in the direction that it never catches the outer lip of the material...


                      • #12
                        I guess on the tractor is won't matter as much when the CF bulbs start smoldering............

                        Sorry couldn't resist, I'm up to two burned-up ones now, and expecting more. Made in china, of course.....................

                        Keep eye on ball.
                        Hashim Khan


                        • #13
                          Evan , it must depend on location if you can get a bottle that cheap in the U.S. I just exchanged my acetylene bottle last month, 43.00 here in NW Okla.


                          • #14

                            do you need to coat the aluminum with anything to stop it from re-oxidizing? if you didn't coat yours, how long do you think they will stay shiny? i haven't played around with polishing aluminum lately, so i'm just wondering if the reflectors will need to be pulled off and re-polished every few months, or if you think they will stay reflective for a long time (the life of the bulb, optimally).

                            andy b.
                            The danger is not that computers will come to think like men - but that men will come to think like computers. - some guy on another forum not dedicated to machining


                            • #15
                              I dunno if you'd want to, but i think you should submit your article to the magazine. I would think it would be popular with the whole "save the environment and use less electricity" fad (not that i'm not all for helping the environment but some of the stuff seems pretty political) and its an easy but rewarding project for a beginner.

                              just my two cents....