3.3 Dimmability and its price

There have been various methods around to achieve the dimmability of fluorescent lamps with magnetic ballasts, ranging from phase angle control to an inverter feeding a whole lamp arrangement with a variable frequency. The problems were, especially in the former case, the increasing flicker when dimmed down low and to keep the lamp from extinguishing completely. Methods such as longitudinal electrodes paralleling the lamp and permanent filament heating were the more or less satisfactory solutions, the latter of which decreases the energy efficiency and makes dimmability doubtful if used in order to cut electricity costs. The variable frequency was not so much different from the use of electronic ballasts today, only the frequencies were lower and the magnetic ballast on top of electronic frequency inversion still needed. At 50 Hz, the full power was fed into the lamp, while as frequency rose, impedance of the ballast became higher, so the current dropped, while the voltage across the complete luminaire remained largely stable. Therefore and on account of the higher frequency the light flux was also more stable than with phase angle control, but after all the method was not so much cheaper than equipping each lamp with an individual dimmable electronic ballast. A new dimming technique for magnetic ballasts is presently being developed in Canada), which seems quite promising but is not yet commercially available on the market. So until today, if dimmability is required, the choice is still an electronic ballast, while the stand-by consumption of these (mind section 8.1) remains an issue! Moreover, the dimming feature does not come together with an electronic ballast without mentioning (Fig 7), as is sometimes believed, but rather doubles the price once again (Table 3.1), which is already very high in comparison to even a high-quality magnetic ballast. The quoted prices per piece are valid for a quantity of one unit package, which is usually about 20 pieces, and possible rebates for larger lots range from 0% to a maximum of 50%. For OEM equipment being traded to the luminaire industry in tremendous piece numbers a substantially higher rebate may be possible. The unfortunate consequence of this is that the luminaires are then equipped with electronic ballasts by default, and customers who do not purchase huge quantities will be served with magnetic ballast luminaires not even on demand, however justified their desire may be (see section 7).

The prices of electronic ballasts are valid for those with a warm start as well as the so-called cut-off features, which is the only fair comparison. A cold start electronic ballast without cut-off technology comes at 47.50 € from Vossloh-Schwabe (0). Both warm start capability and cut-off technology are appreciated as a valuable extra with electronic ballasts, while they come without mentioning, enforced by the principle, with magnetic ballasts, be it with electronic starters or with the poor conventional glow starters.

Table 3.1: Catalogue prices for a 230 V, 50 Hz, 58 W ballast

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