Note how there is a paucity of blue in the top, ordinary tungsten domestic light bulb, and inspite of its blend with tungsten, the Mercury lamp still has rather narrow spectral lines, which should make it easier to filter out. However, technology marches on and the current-technology Energy-Saver bulb has spectral lines all over, making notch filters less effective. This bulb is supposed to be "Cool Daylight" typical for use in offices and consequently has extra attention paid to the blue/violet side. I am impressed at how the design of this latest-technology lamp dumps most of the energy where it matters, in the range of visible wavelengths. Rather than present you tons of data (that I did gather) I decided to narrow things down to only the results with the Energy Saver, possibly a tougher test than much existing, old, street lighting (i.e. this lamp contains numerous spectral lines sprinkled all over the place) but definitely the likely trend for the future. Human vision spans, roughly, wavelengths between 4000 and 6500 Angstroms, so the above also presents what happens in the Near Infra Red. Note the location of the most important emission-nebula lines; Hb (Blue), OIII(Teal) and Ha(Deep Red, at around the limit of human vision). For most emission nebulae, these are the brightest spectral lines. The other marker tags are simply for my own use when calibrating a captured spectrum to the Angstrom axis. It is unfortunate, however, that even emission nebulae have in addition, reflective and other esoteric-emission regions that are too many and varied to be captured fully using single-line narrowband filters. Consequently, narrowband imaging of most nebulae is very unlikely to replicate a straightforward, deep capture in white light at a very dark site. But there are a few popular targets, e.g. the California Nebula and the North American that can be captured in a very satisfying manner using a very narrow H-alpha filter, even at a highly light-polluted site. When one adds the capture of OIII in narrowband one adds a whole slew of targets that can be imaged quite nicely with simply 2 narrowbands, OIII and Ha. Still, one has to admit that there is a gradation of targets vs skyfog vs narrowband imaging. The primary message from the above is that not all fluorescent lamps are created equal. There are a few major common spectral lines that the astro notch filters attempt to block; but depending on the precise, proprietory gas mixes and phosphors that a particular bulb manufacturer has used, it would appear that, inevitably, we can expect some rogue emission lines that will leak onto the camera sensor. The only "perfect" solution is to use very narrow filters and image each nebula line individually (tiresome!) or compromise and use a more crude duo-tone filter concentrating on OIII and Ha only. The narrower the two passbands are, the more the filter will reject the spurrious spectral lines from street lights (very desirable) but the more they will also reject the more esoteric emissive lines from a nebula, and also the nebula's reflection spectrum (undesirable). Often it is these "other" lines that lend a certain delicacy and overall enhanced beauty (OK, sounds like wine tasting or audio HiFi!) to the multi-colored nebulae.

If your monitor screen is large enough please click on "original" below right to view the images more comfortably. It's like astro filters; the convenience of a tiny netbook compromises on screen size. The cleanliness of narrowband captures compromises beauty ;-)