Hello, Crinju. Thanks for posting.
I think approximate current draw is determined via the environment that the sensor is subject to. I don' think we can give an approximate value, however, I can give you an idea on how much current it may consume below.
According to a document I have found regarding phototransistors:
"When the phototransistor is placed in the dark and a voltage is applied from collector to emitter, a certain amount of current will flow. This current is called the dark current (ID). This current consists of the leakage current of the collector-base junction multiplied by the dc current gain of the transistor. The presence of this current prevents the phototransistor from being considered completely "off", or being an ideal "open" switch.
The dark current is specified as the maximum collector current permitted to flow at a given collector-emitter test voltage. The dark current is a function of the value of the applied collector-emitter voltage and ambient temperature."
According to the datasheet for the TEMT6000 https://www.sparkfun.com/datasheets/Sen ... MT6000.pdf
"Collector dark current VCE = 5 V, E = 0 ICEO 3( 50 nA)
Collector Light Current Ev = 20 lx, standard light A Ica 3.5 10 (16 µA)"
I hope this helps.