Koninklijke Philips Corporation N.v.

Philips Electronics North America Corporation

Wolfgang Doetter

Erik Paul Boonekamp

Ray G Gibson

Johannes Adrianus Frederikus Peek

Eduardus Johannes Cottaar

The electric lamp employs a lamp vessel ( ), which is transparent to visible light and which accommodates a light source ( ). The lamp vessel ( ) is covered with a combination of a light-absorbing medium ( ) and an optical interference film ( ) employing layers of alternately a first layer of a material with a comparatively high refractive index and a second layer of silicon dioxide. A spectral transmission T of light transmitted by the light-absorbing medium ( ) changes from T&lE;0.15 to T&gE;0.75 in a wavelength range having a width &lgr;&lE;50 nm. The variation in reflection R amounts to less than 10% in the wavelength range 400&lE;R&lE;690 nm, the reflection R and lies in the range 50&lE;R&lE;90%. In operation, the electric lamp emits colored light in the transmission mode and has a substantially color-neutral appearance in the off state.

Electric lamp

Thin film interference filter consists of alternating first and second layers, the first layers being silica, the second layers being a mixture of tantala and niobia. The filter may be used on a high temperature lamp in an inert atmosphere if the niobia in the mixture is less than 40% by weight. For higher percentages a partial pressure of oxygen has been found to prevent blackening of the layers.

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Aachen, Germany

Wolfgang Doetter