In this paper we describe the "Ambient Timer", a tool to assist users in task switching in an office context. We use ambient light to notify users in an unobtrusive way that they have to finish one task and get on to the next one. We have created a prototype and have evaluated it in a lab study with seven participants. Results of our pilot study suggest for potential for exploring the design space further. Overall, participants response to our prototype was positive. A long-term evaluation in

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... e wild" should be conducted to further explore the utility of this ambient light display.