How to Measure Sunlight in Watts for a Room

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Discussion Overview

The discussion revolves around methods to measure the amount of sunlight entering a room, specifically in terms of power measured in watts. Participants explore both direct measurement techniques and approximations, considering various factors that influence sunlight intensity.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • One participant inquires about devices for measuring sunlight and seeks approximation methods for sunlight energy entering a room.
  • Another participant notes that the power of sunlight at noon on the equator is approximately 1 kW per square meter but emphasizes the variability due to multiple factors such as time of day, season, and obstructions.
  • A different participant suggests using a solar cell with a known efficiency curve attached to the window, measuring voltage across a load, and calculating power produced while considering efficiency and window size.
  • This participant also clarifies that total energy over time should be expressed in watt-hours rather than watts.

Areas of Agreement / Disagreement

Participants express agreement on the variability of sunlight intensity but propose different methods for measurement and approximation, indicating that multiple competing views remain regarding the best approach.

Contextual Notes

Factors influencing sunlight measurement include the angle of the window, direction faced, latitude, and environmental obstructions, which are acknowledged but not resolved in the discussion.

TSN79
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I need to measure the amount of sunlight that enters a room over a given period. I assume I'll need to get my hands on some device which can measure this, but in the meantime, is there a way to approximate how much light/energy enters the room at a given time? The best would be to get a Watt approximation...
 
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The power at noon on the equator is about 1 kW per square meter. However, sunlight is incredibly variable, owing to time of day, time of year, angle of the window, direction the window faces, latitude, cloud cover, trees or other obstructions, you name it.

- Warren
 
Yeah, that's exactly what's making it hard...
 
Buy a solar cell having a known efficiency curve [data usually found online] and attach it to the glass in the window, facing outward. Apply a constant load the the solar cell - a resistor. Meausure the voltage across the load throughout the day and write down the data. Calculate the total power produced for any point in time, compensate for the efficiency, and scale up for the size of the window. You can do this for a few bucks though you may need to buy a $5 meter at Radio Shack. Also, if you want the total energy over a period of time then the final answer for would be in watt-hrs, not watts.
 
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