Solar Freaks

Hi everyone,

I want to make a custom LUX/Light meter with a spare solar cell that i have. How can i do this? I want to build one so i can understand the concept within a LUX meter, therefore i don't really want to buy one.

1 more question, how do you find out the percentage on light it is?

Thank you,

Karo

Hello Karo,

The sunlight meters that are used to measure sunlight percentage at events are made up of ordinary solar cells and measure their short circuit current output with an ammeter or multimeter. You can easily make your own.
These work on the principle that a cell's short circuit current is directly proportional to the sun intensity. In other words, half the current is produced at 50% sunlight, 25% the current at 25% sunlight, etc.

At the last few nationals sun intensity has been measured using a couple of dicksmith modules in parallel and taped off to produce 1amp at 100% sunlight. This makes reading the multimeter easy since, for example, 63% sunlight would read 630mA, 27.5% would equate to 275 mA and so on. Likewise, a cell could also be taped off to produce 100mA instead of 1A at 100% sunlight.

Of course you don't even have to do this. Any cell will do. You just have to calculate the percentage if you want it on a 0% to 100% scale. For example, if a single dicksmith module, which say produces 550mA at 100% sunlight, is used instead then 63% sunlight would read 63 / 100 * 550 = 346.5mA. Going the other way, 215mA would equate to 215 / 550 * 100 = 39.1%.

The problem with these meters is what do you call 100% sunlight? They are all relative. Unless they are somehow calibrated to a standard, some meters may show sunlight percentage being at 90% while others 110% at the same time. The light meters used at the various events by the time keepers are reasonably consistent with one another though and are calibrated.
A meter that you make at home might however end up being a little different but this doesn't really matter. If you set up your own meter for testing, just make sure you then use that same meter on competition day to help you decide on gears, motors, etc.
Just go out at midday on a sunny day in summer, measure the current and call that 100%. If you want to get a nice figure like 100mA or 1000mA for 100% you‘ll probably need to tape over some of the cell/s as mentioned a little earlier.
You can still go out and measure the current even though it is now March. Your meter will then just read a little over 100% in full sunlight during summer.

miseli

I forgot to mention in the previous post that Scorpio Technology http://www.scorpiotechnology.com.au/ are now selling a calibrated solar cell module (panel #10 in the solar catalog) that has been designed specifically for use, in combination with a multimeter, as a sunlight meter.

These modules are fully encapsulated and are meant to be calibrated to produce 100mA short circuit current at 100% sunlight. The mA reading on the multimeter therefore translates directly into a sunlight percentage.

miseli