Overhead Projector: 3M, Elmo, WolfVision, Liesegang?
Since projectors were introduced to the market, the familiar overhead type has become completely outdated. This fact means that you don't have to part with much cash at all for a model with high luminosity. If your main concern is functionality, you could go for an older device with an old-fashioned housing, and save even more. Used projectors can be picked up for around $50.
A prime consideration when buying a projector is the brightness, which mainly depends on the lamp used. We used a simple data projector from Liesegang (OHP 2510), equipped with a 400 W halogen lamp , which, according to the datasheet, produces 3,500 ANSI lumens. The top-of-the-line models feature HQI lamps of 600 W and even more.
As most of the energy is given off as heat loss, operating a projector means the surroundings become heated. Most importantly, the LCD panel must be sufficiently cooled to prevent any damage. We have included a special section on this.
Simple construction: the opened overhead projector with bulb holder, transformer and fan
A major advantage of a projector with a normal halogen lamp is its price: replacement lamps are available for less than $30, where HQI lamps are much pricier. Here, too, it's worth comparing with the projector we settled for. Its lamps costs upwards of $200 each - the manufacturers take this into account in the overall price calculation.
If they break, these halogen lamps cost $30 dollars at most - but a lamp for a new device is at least $200!
Our recommendation when all's said and done: for good illumination and adequate brightness, your projector should have at least a 350 W lamp. At low brightness, the room has to be effectively darkened to achieve a good picture on the screen's large dimensions.
Lamp socket: in our case, it is designed for a maximum of 400 W. Metal halide lamps are also available for 600 W and more.