Answer:
insufficient strength of the manipulation
Step-by-step explanation:
The non-significant results may have occurred because of insufficient strength of the manipulation. Since the variable being tested in this scenario had a very slight difference it caused insignificant results. The variable in the study (light bulb) needs to be drastically different in order for it to have an effect on the subjects and provide results that differ. The 100-watt and 125-light bulb provide almost the same luminosity levels.