stealth technology

[g8rdotony]

Previously asked a question about doing the stealth technology experiment using a laser instead of the LED flashlight as suggested. Have now completed the experiment. Painted the inside of box with "camouflage" black paint by Rustoleum that is supposed to be 20% less reflective than flat black matte paint. Lux readings on empty box are 0.0. Average reading on the cylinder is 0.86, crumpled paper cylinder is 0.7, V-shape is 0.5 and W-shape is 0.3. This seems to support hypothesis that the W-shape would reflect the least light and thus be the most stealthy. Question whether these readings are valid/accurate as they are all less than 1 lux. Shapes were placed approximately 15 inches from the laser and light meter - readings at this distance and shorter distances stayed the same. Would a longer distance affect these readings? Would you say out hypothesis was correct of that cannot prove or disprove hypothesis due to extremely low lux readings?

Thank you.

[deleted-71882]

Hello g8rdotony,

As you noted in one of your previous posts, the laser illuminates only a small spot on the test object, so the scattered light indicates only the properties of that small spot. If you want your results to correspond to the situation in which an aircraft or other extended object is illuminated, you would need to use a flashlight or other light source that illuminates the entire text object. If you have an optical lens available, you might be able to place it in front of the laser and spread the laser beam.
The fact that all your readings are less than 1 lux doesn't necessarily mean they are wrong. The reading you get depends on both the brightness of the light source and the properties of the test object. To get a feeling for how large the reading might be, try recording the reading from a flat sheet of white paper.
Whether a longer distance from the test object to the meter would change the reading depends on how big an area on the test object is viewed by the light meter. Since your readings remained the same for 15 inches and shorter indicates that 15 inches is okay, but longer distances might begin to view part of the black background and give lower readings.

[g8rdotony]

Thank you for your response. The reading on a flat piece of paper was 0.5 lux.

Originally planned to do project as suggested with flashlight, but got overuled by science teacher who preferred the laser. Not allowed to use any optical devices due to risk assessment guidelines as this could apparenlty intensify the laser and cause eye damage.

Family feels tight beam of laser hitting just a small portion of object and not assessing angles/shape of hte objects, but 6th grade student very happy that hypothesis seems correct.

[deleted-71588]

Originally planned to do project as suggested with flashlight, but got overuled by science teacher who preferred the laser.

Scientists shouldn't be afraid to color outside the lines! Earlier I recommended that you do each of the experiments TWICE, once with the laser to satisfy your science teacher and again with a flashlight to satisfy your curiousity. IMO: Any science or math teacher that discourages a student from doing more work doesn't belong teaching math or science. If you get the results I expect (that the light source significantly affects the result), then I would report that result. Teachers can learn things from well done student science experiments.

As to the safety of spreading out a pen light laser beam, the energy concentration decreases which decreases the safety concerns. The danger with any and all light sources is an unexpected reflection or refraction that directs the light somewhere it wasn't expected to go. Does your Mom have one of those "magnifying makeup mirrors"? If so, you can safely use it to spread the beam because you can predict where the reflection is going to be using a flash light. A pen light laser beam with the same incident angle on magnifying mirror will reflect inside the reflection of where the flashlight beam went.