Wireless optical links with intensity modulation and direct detection are widely used for short-range communication. For indoor applications, the main source of interference is artificial lighting. The emitted optical power of fluorescent lamps with reactive and electronic control gears as well as light emitting diodes is measured and analyzed in time and frequency domain using Welch power spectral density estimate and spectrogram with short-time Fourier transform. Driven by the need for energy efficient lighting, the optical interference environment undergoes a radical change from low-frequency incandescent lamps and conventional fluorescent lamps to fluorescent lamps with high efficient, high-frequency electronic control gears and LEDs with pulse-width modulation dimming. Based on the interference measurements, a model of the wireless optical indoor channel is presented.