Science Fair Project Help? PLease? Pretty Please?

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YoHoHo Shop
Last seen: 7 years 2 weeks ago
Joined: 10/05/2014 - 14:18
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Science Fair Project Help? PLease? Pretty Please?

So, i was thinking about making this, as a science fair project. My project is about finding the “Best” Light bulb. I am measuring several different things, and lumens are one of them. I would like to know how to use an illuminating sphere. Thanks!

BTW: IF you help, i would be eternally grateful. Smile

Arrgh ye ye cowardly fools! I’ll skewer you on the banks of the great Mississippi. I’ll take yer bones to the 5 great shops throughout the land, and I’ll sell them for but 10 gold doubloons! Arrgh!

Edited by: YoHoHo Shop on 10/05/2014 - 14:35
DaveO's picture
Last seen: 6 years 5 months ago
Joined: 09/23/2013 - 00:38
Posts: 21
Location: Sydney

As per the original post.
You need a reflective, but diffuse sphere, with two holes and a baffle. The light source goes in one hole and the light meter in the other (behind the baffle, to avoid direct light). You’ll also need a known light source for initial calibration. You can use a iPhone if you can’t afford a proper light meter.

For non directional light bulbs the entire light needs to go into the sphere. So the sphere also needs to be fairly large. You also need to try and keep it all at a constant temperature. Especially for LED testing.

The other option is to make your own goniophotometer. We made an automated unit, with a stepper motor, but it is fairly easy to make a “manual” goniophotometer where you manually move the light meter around the globe.

The advantage of the sphere is speed of measurement and no maths is required. The advantage of the goniophotometer is that you can also measure the light distribution (e.g. polar diagram, lux at the center of the beam, beam angle).