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. Author manuscript; available in PMC: 2016 Dec 16.
Published in final edited form as: Neuron. 2015 Nov 29;88(6):1136–1148. doi: 10.1016/j.neuron.2015.10.032

Figure 3. Characterization of the μLEDs.

Figure 3

(A) Current versus voltage.

(B and C) Optical power and plug efficiency versus current, respectively (mean and SEM, n = 5).

(D) Light intensity modeling in the brain along the main axis of the μLED (perpendicular to the probe surface) at a logarithmically spaced array of light power. At 4 μW (at which iHFOs are consistently generated, Figure 6), intensity falls below 1 mW mm−2 by 37 μm from the μLED; at 40 nW (at which local spiking is consistently induced, Figure 4), intensity falls below 0.1 mW mm−2 by 6 μm.

(E and F) Thermal modeling of μLED during continuous operation at various bias voltages: (E) μLED surface temperature rise over 10 s; (F) time required to elevate the brain temperature to 38°C at various distances away from the μLED surface.

(G) Thermal modeling of μLED using 5-Hz sinusoid voltage bias waveforms: the temperature rise follows the light power waveform (blue dash, normalized) rather than the voltage command (black dash, normalized), with minimal heat accumulation after five cycles. See also Figures S1 and S2.