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Idea for LED Rainbow Light

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Hi Stephen,
Many years ago I designed and made a bunch of slowly fading ultra-bright gadjets that shine their red, blue and green LEDs on the ceiling. I used opamps as oscillators and to make the current ramps at slightly different rates so that all colors and brightness levels slowly appear randomly. Since the LEDs draw current continuously they are mains powered by a wall-wart adapter.

A couple of years ago a similar Chinese product was available at Wal-Mart cheaply. It is controlled by a microcontroller and has a selection of many combinations of LED patterns and surf, wind and waterfall sounds. It has a glass ball with many small bubbles for the LEDs to light. Batteries (three AA cells) would last only a few evenings so a wall-wart adapter powers mine.

A year ago I bought some cheap Chinese solar-charged garden lights that use an RGB ultra-bright LED that shines on a fractured-glass ball. Their two AA 600mA/hr Ni-Cad cells power them all night long after a full day in the sun for recharging. They are bright enough at night to light the ceiling of my bedroom on the 2nd floor pretty far away. The 3 colors brighten up then fade down one-at-a-time.

None of these things make a rainbow. They just project slowly changing single colours at slowly changing brightness levels at their ball or at the ceiling.
A white LED won't make a rainbow if shined through a prism. It is only a blue LED shining through a translucent yellowish phosphor. An RGB LED has separate color chips inside so might be able to make a rainbow with a prism.

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