Amateur astronomy has long been a pursuit that loves to debate the controversial topics, even from its earliest days. All those hours spent studying, observing and watching the sky frees the mind enough that it can form hypotheses and compare them with those of nearby observing companions. The earliest known controversy occurred one night long ago when one observant dinosaur looked to the heavens and said, "Look, a meteor! I think it's going to hit the ground!" His observing buddy looked up, pondered the scene for a moment and said, "No it isn't." History doesn't record for us the rest of that conversation. Thus was established the scientific method as it's typically practiced in amateur astronomy circles. These discussions contributed to some of the most fundamental philosophical changes ever conceived in the early 1600's when everyone in the world said "The Earth is the center of the Universe". To which Galileo simply replied, "No it isn't."
A topic that seems to generate slightly less debate amongst modern amateurs is the subject of star party light pollution and there' s no shortage of opinions on the topic. With the advent of electronic go-to telescopes, CCD Cameras and modern astronomical software the laptop computer has invaded star parties worldwide. The encroachment of electronics onto the observing field has been one of uneasy tension since the successful release of the Meade LX200 line of go-to telescopes back in 1992. The noise of the coffee grinder mount slewing across the sky forever changed the landscape of the star party. In the years since, more and more electronics have come to the observing field. Among them has been the advent of the laptop computer and a significant amount of controversy.
Some observers swear by them and their use in the field. Some observers insist that they're a nuisance and have a disruptive influence on productive visual observing. The modern astrophotographer has little choice but to use a laptop computer in the field for CCD imaging. The problem is that a laptop computer can generate an enormous amount of unwanted light on the observing field if they're not properly shielded. Some would maintain that it's not possible to properly shield a laptop computer in the field to preserve night vision. For someone who has a deep love of hopeless addiction to astrophotography like I do this presents a conundrum. I also enjoy visual observing and the fellowship of observing with other members of my club. I was quite cranky when astrophotographers were sequestered to a separate end of the airstrip at this year's Messier Marathon. "My laptop and the way that it's shielded is less damaging to night vision than many of the red lights that I see on the observing field on any given night!!". "Why do we have to go to the North end of the observing field? The visual observers should have to move to the south end if it bothers them so much!!" My own reactive hyperbole does nothing to further the discussion or find a way for all observers to co-exist peacefully. So instead of writing my own defensive but highly entertaining rant, I've opted to stage my own informal experiment to compare the effects of various observing field light sources on night adaptation.
Test Subjects
My test is designed to measure the amount of light pollution generated by five different test subjects:
· Laptop Computer - Unshielded: Anyone not named Ray Charles knows that this will be the most obnoxious test case in the group. The test will be done using a 16.4" Sony laptop and a SkyTools 3 generated chart of M31 with the laptop screen at full brightness. No red film or "night vision mode" is employed for this test.
· Laptop Computer - Shielded: Naturally this will be a test of the laptop as I use it in the field. I have used a laptop for almost 10 years in the field, even for visual observing. The test will be done using the same laptop and a SkyTools 3 generated chart of M31 with the laptop screen at minimum brightness and covered with a sheet of fitted, dark red acrylic plastic. In addition, the "night vision" mode implemented by SkyTools 3 will be turned on.
· Regular Star Chart/Dim Red Light: A common red LED flashlight (Celestron Item #93588) with the dial set to "minimum" and a chart from Uranometria 2000.0. The light itself will be suspended over the chart about 8 inches (20cm) away from the paper to approximate a typical observer's use in the field.
· Regular Star Chart/Medium Red Light: The same LED flashlight with the dial set to its halfway point and a chart from Uranometria 2000.0. The purpose of the medium light test is to establish a result for a standard red light that is typical of an average observer's use.
· Regular Star Chart/Bright Red Light: The same red LED flashlight and Uranometria chart, this time with the brightness dial set to "maximum".
Test Conditions
· The Eye: To provide an objective means of measuring the results I employed a Canon 60D DSLR camera operating at ISO 800 with an 18mm f/3.5 lens. This is in an attempt to approximate the optical specifications of the average human eye without a negative impact on the financial specifications of this particular observer's bank account.
· The Measurement: Each test subject will be photographed in a darkened room in aperture priority mode. By using aperture priority mode, the camera will adjust the length of the exposure based on the amount of light hitting the light meter (center weighted average metering). A shorter exposure indicates a more destructive light source. A longer exposure indicates a more night vision friendly light source.
· The Observing Conditions: Measurements will be taken from two distances. The first will be from 30 inches (76 cm) to approximate the effect of the light source on the observer that might be using it. The second will be from a distance of 10 feet (3 m) to approximate the effect of the light source on a nearby observer.
Test Results
I conducted all of the photography in my state of the art darkened laboratory which also doubles as the storage room for my astronomy and camping gear in its spare time. I conducted all of the tests as described before learning that there wasn't a memory card in the camera. I put a memory card in the camera and conducted the tests again. The table below lists the results of each test scenario. As would be expected an unshielded laptop computer will instantly turn you into one of the fabled three blind mice. The main point of the experiment though was the comparison of a shielded laptop with that of a standard red LED flashlight. Results show that a properly shielded laptop computer is no more damaging to an observers night vision than the ubiquitous red LED torch that we all use - placing 2nd overall of the five test cases.
In the table below are the test results listed in order from the dimmest to the brightest. The 2nd and 3rd columns show the results of the tests from a distance of 30 inches. My patent pending and proprietary "Fried Retina" Factor measures the additional light output of each additional test when compared to the dim red light test. For instance, an unshielded laptop is 250 times brighter than a dim red light. The 4th column shows the test results as measured from a distance of 10 feet - designed to measure the effect of the light source on nearby observers. The magnitude column attempts to express the results in the form of star magnitudes as another basis of comparison. For instance, if an unshielded laptop is equivalent to Vega (0.0 magnitude), then a dim red light shines with the magnitude of a 6th magnitude star.Test Case | 30 in. Exposure | FR Factor* | Magnitude | 10 ft Exposure |
Dim Red Light | 5 seconds | 1 | 6.0 | 8 seconds |
Shielded Laptop | 3.2 seconds | 1.56 | 5.6 | 6 seconds |
Medium Red Light | 2 seconds | 2.5 | 5.0 | 8 seconds |
Bright Red Light | 1/3 second | 15 | 3.4 | 4 seconds |
Unshielded Laptop | 1/50 second | 250 | 0.0 | .6 seconds |
*FR Factor - Fried Retina Factor
My own subjective thoughts on the experiment:
Dim Red Light: The output created by the light source at this setting would have been unusable for me. Ten years ago I would have been able to use this light with a chart, but there's no way that I could do it now with my aging peepers. I believe that very few observers would be able to use the light at this dim setting.
Shielded Laptop: The laptop with all of the shielding methods in place is a about 1/2 f stop brighter than a dim red light. This is right in line with a typical observers red flashlight that I typically see on the observing field. I did find it interesting that at a distance of 10 feet the laptop appears to be marginally brighter than a red light at medium setting. This is almost certainly due to the fact that it's still a backlit light source.
Medium Red Light: This light setting is a touch brighter than what I see from most observers at a star party and would be too bright for me to use without damaging night vision unnecessarily. I actually added this test after completing the other four in an effort to provide a fairer comparison of real world conditions.
Bright Red Light: This light was really, really bright. I can say that I've never seen an observer use a red light to look at a star chart at this setting. I have used a light at this setting when crossing the observing field to keep an eye out for tripping hazards like dark colored dogs sleeping on the ground or random satellite dishes. Don't laugh. I've found myself face first in the ground because of both.
Figure 1: Comparison photo showing a 3.2 second exposure of a shielded laptop, and a medium brightness red LED flashlight.
Conclusion
In a case of astronomy imitating life, everything old eventually becomes new again. The laptop computer, go-to hand controller and smartphone are simply new expressions of an old issue: proper light control. A properly shielded laptop is no more damaging to night vision than a properly shielded flashlight. Even with the influx of technological advances to the observing field the age old task of maintaining proper dark adaptation is still the same, just in a different form. Without question, there are additional precautions necessary with many laptops. In my case I generally take four steps with my laptop on the observing field to properly shield it for myself and my fellow observers:
1. Red Fitted Acrylic Cover: I cover the laptop screen with a dark red fitted cover and tape it down to prevent any unfiltered light from leaking out of the screen. These can be custom ordered from http://www.tapplastics.com/shop/product.php?pid=519 . I also cover every indicator light on the laptop with electrical tape.
2. Red Light Mode: Most charting/observing programs have a night mode that will turn everything on the screen to a red light type of color scheme in an effort to help. I use SkyTools 3. The red light mode in Sky Tools 3 turns everything on the screen black and all of the relevant text to a deep red. In conjunction with a red plastic cover, the screen is very readable.
3. Adjust Screen Brightness: I adjust the screen brightness to be as dim as possible. These three steps were taken to create the results in these tests on a 16.4" laptop screen.
4. Point the screen to the North: I try to setup so that the laptop screen itself is always pointed to the north on the observing field. Few observers are ever trying to observe an object that is low in the north, so this setup puts my screen out of the line of fire of almost every observer on the field.
I don't expect that this will be the final word on the subject. Astronomers love a lively debate and this will continue to be debated long into the future. I simply hope that my admittedly unscientific experiment has added to the discussion in a positive manner.
