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Salvage It! BY JULIAN EDGAR Using the convex lenses from fancy car headlights Good quality convex lenses can be salvaged for next to nothing from car wrecking yards. Here’s how to use them to make a really bright handheld spotlight or a broad-beam bike light. W HEN YOU WATCH cars go by at night, you can see a variety of headlight designs on display. For example, old cars use sealed beams which are often rather yellow in appearance. Then there are the whiter designs with replaceable halogen bulbs, while recent luxury cars feature high intensity discharge lights which have a brilliant blue/white colour. Projector headlights There are also lights which, when viewed at an angle, have red or blue beams graduating to white as the car is seen face-on. These headlights have an abrupt beam cut-off and a very even spread of light within the beam. They are known as “projector” headlights and use a simple reflector teamed with a large convex glass lens. Want to know something? Those A projector headlight is easily recognised because of its convex glass lens. 72  Silicon Chip large glass lenses can be obtained for nearly nothing from broken headlights at car wreckers. Want to know something else? They make excellent lenses for use in bike lights, torches and handheld spotlights. Fig.1 shows a typical projector car headlight. From the front, there’s a cover plate of glass or plastic. Behind that is the convex glass lens (normally used only on low beam), followed by the bulb and then a simple reflector. The bulb is masked so that the upper part of the beam is abruptly cut off, to avoid blinding oncoming drivers The single headlight assembly also contains a high beam, which usually comprises a conventional halogen lamp and a reflector. The headlight is near worthless to the wrecker if the cover glass is broken, the high beam is broken, the low beam is broken or the rear plastic housing is shattered. However, if the low beam convex glass lens is intact, the convex lens can be bought for next to nothing. For example, at a major wrecking yard, I found and salvaged three convex lenses and took them to the front counter. I made the point that I hadn’t needed to break any headlights to obtain the lenses and asked for a price. The man behind the counter was puzzled: what on earth did I want these lenses for? I told the truth – I was making a bicycle headlight – and he charged me $10 for all three. On another occasion, when I was buying some other car bits, the convex lens didn’t cost me anything extra. Many recent cars have projector headlights while amongst older cars, the Mazda 626 and Ford Telstar are the siliconchip.com.au Large convex glass lens are easily salvaged from wrecked car headlights that use a “projector” design. These lenses use high transmission glass and are optically accurate. most common. Some Nissan imports also have them, including one car that has two such lenses each side. If you are salvaging the lens from a headlight with a broken cover glass, be very careful. It is extremely easy to cut yourself on the shards of glass, especially if you slip while wielding a screwdriver. Incidentally, smaller lenses of a similar shape can also be salvaged from old slide projectors. Using the lens So you have a bunch of high-quality, large, convex glass lenses that you’ve obtained for nearly nothing. Now what? I could get all theoretical and talk about focal lengths and beam angles and point sources but let’s forget all that. The easiest way of coming up with the best design for your particular application is to simply play around with the light source and the different lenses. For example, a Luxeon LED makes an excellent light source as it is small, very bright and has high efficacy. Power-up the LED (after mounting it on a suitable heatsink if it’s a 3W or 5W design) and hold the convex lens in front of it. Now view the beam pattern on a wall or the ceiling. By altering the distance between the lens and the LED, it’s possible to change the beam from a broad diffuse beam to a narrow spot. In the case of the Luxeon, you can also try matching the glass lens with the various collimators available for these LEDs. The lenses can also be used with siliconchip.com.au This photo shows the components needed for a bright, wide-angle light (from left and then clockwise): convex glass lens salvaged from a projector car headlight; shortened stainless steel drinking cup and bracket made from aluminium angle; and a 1W Luxeon LED and narrow angle collimator mounted on a salvaged aluminium block. Missing from this photo is a cut-down U-PVC plumbing cap to hold the lens in place over the end of the cup. Fig.1: this diagram shows a “projector” type car headlight. The main optical element is a large convex glass lens mounted within the headlight assembly (1) and this replaces the reflector and flat glass lens used on other headlights. A shield (2) prevents on-coming driver glare, while (3) is the rudimentary headlight reflector and (4) is the bulb. [Bosch] conventional incandescent bulbs and reflectors (and incidentally, lots of working torches with perfectly good reflectors are thrown away each day). Again, it’s a case of trying different combinations and looking at the results. If the lens is placed very close to the light source, it’s possible to get an extremely broad beam, which greatly November 2006  73 The Luxeon LED, its collimator and the mounting block are attached to the base of the cup using screws and nuts. The convex lens fits over the mouth of the cup to provide a broad, even beam. enhances its visibility at night. It’s just the shot for a flashing warning light or bicycle tail-light. Building a compact light I used a convex lens from a car headlight to make a very bright, broad beam, flashing tail-light for a bike. First, a stainless steel drinking cup was shortened in length using a hacksaw and file. This gave a housing with an opening that matched the diameter of the lens. A 1W red Luxeon LED and a narrow-beam collimator were then installed on a small block of alu- They’re Glass The convex lenses salvaged from car headlights are made from high quality optical glass. So if you drop them, hit them or squeeze them hard enough, they’ll shatter! Here the lens has been reversed compared to its normal automotive orientation, with the curved (convex) side facing the light source. This design is being used as a rear light on a road-going recumbent pedal trike. minium (a 1W Luxeon doesn’t need a heatsink but having one doesn’t hurt), after which the block was mounted in the base of the cup. Next, a U-PVC plastic pipe cap to suit the diameter of the lens was obtained and its inner diameter cut out with a holesaw. This gave a flange that fitted over the end of the cup, holding the lens in place. Silicone sealant was then used to secure the cap in place and to weatherproof the opening. In this application, the best results were obtained by reversing the lens as compared to its normal car orientation – ie, it was mounted with the convex part of the lens facing the LED. The Luxeon LED was powered by a 12V cigarette lighter phone charger adaptor which was modified to act as a constant current source (see “Cheap 1W Luxeon LED Driver” on page 101 of the August issue of SILICON CHIP). A modified “Nitrous Fuel Controller” Rat It Before You Chuck It! Whenever you throw away an old TV (or VCR or washing machine or dishwasher or printer) do you always think that surely there must be some good salvageable components inside? Well, this column is for you! (And it’s also for people without a lot of dough.) Each month we’ll use bits and pieces sourced from discards, sometimes in mini-projects and other times as an ideas smorgasbord. And you can contribute as well. If you have a use for specific parts which can 74  Silicon Chip easily be salvaged from goods commonly being thrown away, we’d love to hear from you. Perhaps you use the pressure switch from a washing machine to control a pump. Or maybe you have a use for the highquality bearings from VCR heads. Or perhaps you’ve found how the guts of a cassette player can be easily turned into a metal detector. (Well, we made the last one up but you get the idea . . .) If you have some practical ideas, write in and tell us! Stainless Steel Cup As detailed in the main text, a stain­less steel drinking cup makes an excellent housing for the convex lens. Single wall stainless steel drinking cups can now be very hard to find but Coastal Kitchen and Cutlery on the Gold Coast (07 5526 9399) have them in stock at $5.50 each. A double wall (ie, insulated) cup can also be used but it is heavier and a little more difficult to cut and drill. circuit (from in SILICON CHIP’S High Performance Electronics for Cars) was used to flash the LED. Modifying the Nitrous Fuel Controller is simple – all you have to do is substitute a 2.2mF 16V capacitor for the original 220nF timing capacitor. This gives a flash rate of about 4Hz, with the duty cycle of the flash able to be altered by the on-board pot. So why go to all this bother when LED tail-light flashers are cheaply available? Well, you’ve never seen a flasher like this. It is extremely bright from directly behind and can be seen at distances of 500 metres or more. The convex lens creates a broader beam than would otherwise be achiev­ ed, allowing the light to be visible over a much wider angle than just having the LED on its own. This effect is further enhanced by reflections from the internal walls of the stainless SC steel cup. siliconchip.com.au