The Compact Fluorescent Bulb Spectrum as a standard calibration spectrum for low resolution spectrometers in astronomy, and comparisons with alternative calibration light standards

I have annotated the following compact fluorescent light spectrum with the wavelengths of the main peaks, in order to make the diagram most useful for spectrometer calibration purposes. I am indebted to Wikipedia for the source information on which this graph is based.


The above is useful for calibrating my CCDSPEC and Science Surplus DIY Spectrometers and other similar spectrometers.

The process involves me taking a spectrum and then identifying the lines on it and calibrating the spectrometer using the process in the relevant software package. This is a spectrum from the Science Surplus DIY Spectrometer of a Compact Fluorescent Light:

The compact fluorescent spectrum can be used to help identify lines on other calibration lights, such as one made from a RELCO neon fluorescent bulb starter:

Further enhancement of calibration can be achieved using alternative calibration standards such as the solar spectrum – here I have annotated that spectrum with the Fraunhofer elemental lines:

Another alternative to calibration standard lights is to use an LED light – this one provides lines in red, green and blue, and is from on a variable colour strip light I purchased from ebay:

Compare the above to a commercially sold white LED calibration light:


Three LED lamp calibration light

I purchased the following multi-coloured LED strip light from ebay – Ed at the last RAG meeting asked whether coloured LEDs could be used as a calibration light for spectrometry – it seemed like a good idea! This one comes with a neat little remote control to allow it to be placed some distance away (ideal for focusing a telescope on it and then turning on and off and changing colours).


I made a calibration light out of the strip light above and a piece of Perspex made to diffuse light (off ebay designed for light boxes). I could then take spectra using my CCDSPEC spectrometer:

The first three spectra show that red, green, and blue are all very pure colours from the relevant LEDs in the strip:

Spectrum of LED strip light – green LED (below):

Spectrum of LED strip light – red LED (below):

Spectrum of LED strip light – blue LED (below):

Producing multiple lines on a single spectrum:

The above graphs demonstrate that the LEDs individually produce pure colours. However, for calibration purposes, it is useful to be able to have multiple lines on a single spectrum. This is where this particular colour-changing LED strip is useful – the strip uses three different coloured LEDs as above but allows you to select various combinations of LEDs to produce variety of “colours” – each of this is a mixture of LEDs switched on together in varying amounts.

The following are three examples of combinations – there are a total of 16 colours available (16 combinations):

Spectra from the three examples of colour combinations:

X-projections from spectra from the three examples of colour combinations:

White colour on the LED strip:

Probably the most useful combination is when all three LEDs are turned on together “white” – donated by a convenient “W” button. The spectrum from this produces three convenient peaks for calibration (below):


Comparing spectra from compact fluorescent lights in lounge, portable 230V desk lamp and portable 12V calibration light

In previous posts, I have discussed the various calibration lights I have tried for my spectrometers. Each time I come back ultimately to fluorescent lights – these have typical spectra and easy to identify peaks and are ideal for relatively low resolution spectrometers such as my CCDSPEC and Science Surplus DIY Spectrometers.

They are available as long bulbs or more compact portable bulbs called Compact Fluorescent Lights (CFL). The spectra are similar.

Initially I used a compact fluorescent light in my study/lounge but then realised I could do with a portable arrangement to take outside into the field. I obtained a simple desk lamp and used 230V CFL bulbs powered using an inverter on my leisure battery. This is not the safest method – 230V can cause harm – but then I found a caravan online shop selling off its last 12V CFL bulbs. I did not realise these were sold in 12V varieties so I have obtained a number of these and built myself a lamp holder than plugs into a 12V cigar-type lighter plug socket so it can be powered from any standard 12V telescope power supply.

In today’s post, I am comparing the spectra on the three sources of CFL bulbs – the ceiling lights in my lounge, 240V desk lamp and homemade 12V mobile calibration system. The question I need to answer is whether all three produce similar spectra – in which case the 12V homemade setup will be my preferred calibration light as it is mobile and safe.

I used my CCDSPEC spectrometer for today’s tests.


Taking spectrum from 240V desk lamp CFL arrangement (below):


Taking spectrum from 12V desk lamp CFL arrangement (below):


Comparing the three spectra:

Spectrum from 240V CFL ceiling light (below):

Spectrum from 240V CFL desk lamp (below):

Spectrum from 12V CFL homemade lamp (below – here I have altered the exposure to give longer and shorter exposures to show that this made minimal difference to the spectrum as long as it did not reach maximum (16000 on intensity at which point peaks broadened and became less useful for calibration as exact wavelengths difficult to read from graph)):


To assist in comparison between the three spectra, I have repeated them below but this time one after the other:

It is amazing how similar these bulbs are – from different manufacturers but still providing same peaks with slight differences only in intensity. It shows that the similar chemical makeup of their constituent gases and that the emission spectra of those gases do not vary.

My conclusion – any of these bulbs can be used for calibration of my spectroscopes and hence I can happily use the 12V outside in the field.

Observing and Imaging 17th September


It’s been a sparse few months for imaging. As well as the short nights of the summer months I’ve also had a few problems with my DSLR, plus the roads around my house have all been fitted with tall bright LED lights (see photo below, showing how much bigger they are) rendering my light pollution filter useless and limiting me to subs <1min. To fight back I’ve invested in the new version of the IDAS filter which offers some relief, plus a second hand Canon 600d with the IR filter removed. Monday was my first chance to use it, and I decided to go for M31 for the purposes of comparison with previous camera and streetlights. After setup I had an hour to try it out and the results are quite promising- I think I’ve gained more from the new kit than I’ve lost from the LEDs. There are some further things that I can do to improve it (I think I can get away with longer exposures, plus I want to try and make a cooling unit for it)- but altogether I’m quite pleased. It’s 20x 180s exposures on a 130 pd-s, with guiding, plus dark, bias and flats.


Whilst the imaging rig was doing its stuff I went for some instant gratification with the Dob. Whilst the LED lighting has hurt the imaging it seems to be better for the visual. At a RAG meeting a while back there was discussion of how counting stars in Pegasus would give you a good indication of your light pollution levels. I went home and found I had a depressing big fat zero. Although the new lights are brighter, they are better directed and I can now see 3 or 4 (faint) stars. This realisation was a good start to an enjoyable session- transparency seemed pretty good, and I doubt there’ll be another session this year where it’s too warm for a jacket. From the observing log:

M71 – Struggled to get my eye in to start with and I found it a tricky find, but satisfying once in.
M15 – Really bright central core and with a ring of resolved stars around it covering around a quarter of the eyepiece at 220x
M2 – Was tighter and not quite so bright or widespread but still a nice view
M52 – Gorgeous open cluster- 30-40 bright stars and many much fainter ones. Tried it at 220x, 70x and 45x and the middle magnification was the best- really filling the view. Highlight of the night.
NGC7789 – Caroline’s Rose – Another nice open cluster- but quite faint, and I couldn’t really see the rose. Maybe it’s like one of those Magic Eye pictures.
M103 – A nice triangular shaped with a lovely red quite central in the Eyepiece.

Monday night’s a bit early in the week to stay up late, and the only downer was packing up as the skies were getting better still. At least I was heading to bed with a full memory card ready for the clouds and rain that have dominated the remainder of the week…


How to turn iPad screen red for observing sessions

Thanks to Damian for these instructions



  1. Settings
  2. General – accessibility shortcut on right at bottom
  3. Colour filters – tick on
  4. General – display accommodations
  5. Colour filters tick on
  6. Choose colour tint
  7. Touch finger on red crayon
  8. Increase intensity right up

Once set up the red colour can be turned on and off by clicking home button 3x in quick succession.

New base for mobile radio meteor scatter operations

Last time I bought my mobile meatiest scatter radio equipment to an outreach event at Rosliston forestry Centre, children were dipping and diving around pegs and ropes holding the ex-military Klansman aerial up. This was identified as a health and safety risk. I have just received the item below – recommended by Ed – it is a wonderfully well-designed piece of kit sold as a mobile stand for garden parasols – it locks both up and down using a spring-loaded mechanism and a metal bit which fits into a slot at the top or the bottom so that it is very solidly held in place in either the open or closed position. It is quite robust be made of solid metal construction, and its ability to fold up makes it easy to transport – bank said for a brilliant idea!


My Clansman radio mast that I am hoping to erect using this base:

Observing 17-18 th October.

Swadlincote 17-18/9/18 Vixen 102 on heq5pro pro mount.

What 4″ of aperture in light pollution can do.

It is a constant source of amazement and pleasure to observe targets from here. We are surrounded by some nine streetlights , neighbours with security lights and no curtains. Using poles and dark throws has quartered off an observing area. It’s also on the hedgehog highway, they have been known to trundle past through the tripod legs.

The night started very favourably with Saturn below a low yellowish Moon. Mars was still wobbling. It was great to set up about eight and finish about two. Some beautiful targets. I haven’t done the research on their stories yet.

It’s often enjoyable just to look at them. I turned to Cygnus as it passed the zenith and again caught NGC 6811 , ” the hole in the cluster” . There was good dark sky action with M27, the blue snowball, Eastern Veil and even a core to NGC 7331.

Here’s a few targets off the beaten track.

Lacerta gives the most stunning background , set in the stream of the Milky Way. Of the open clusters , NGC 7209 is an old favourite. There are some pretty delicate pairs in NGC 7394 and NGC 7245.

Onto a few binaries here , the inline h ( Herschel)1735 being triple. I was very surprised to catch a tiny field star next to the pair of 8 Lacertae. 13 Lacertae is a ticklish challenge.

Then a Star Trek to the northern constellations. NGC 7510 in Cepheus is a wondrous cluster. There is a dusty triangle at low power, like fairy dust ! NGC 7686 gave a beautiful bright shape in Andromeda. I started on the Perseus binaries . Straight away theta Persei gave the most challenging tiny spec of a companion. ΟΣ 81 and DOO 7 I caught in the same view.

No great aperture here (4″), no great magnification , going from x42 to x77 with one at x182. Next time out it’ll be trying out the Baader astrometric eyepiece, to verify some separations and ensure the capture of those elusive faint multiples, under ,

clear skies ! Nick.

M34 multiple stars.

when you look at M34 it’s most appealing feature is the mass of multiple stars on view. I have details of those in M44. Open clusters are mainly young stars .

New stars are formed in the gas and debris loaded arms of spiral galaxies, you can observe new stars in the Trapezium of the Orion Nebula.In the early universe star formation gave a ratio of binaries to triples of 60:40. Later this evolved into a ratio of 65 binary : 25 triple : 35 singles. Gravitation pulls apart open clusters , one of the biggest we can see is Ursa Major . The whole of the plough is a moving cluster apart from the first and last star.

I got the whole wide view , but found a more detailed drawing showing the main multiple stars. Just using a 4″ scope , these are very accessible.

Next time I”lol use some more magnification to get these stars and increase the contrast. I also had look at Sigma Cassiopeiae, a lovely delicate view, under clear skies ! Nick.

Message from George – Greek astronomer from Skopelos

Hi Folks

I had a reply from George Mihail that I met in greece. It’s worth having a look at his website. Very interesting setup, a great view. The last photo is the latest live feed from his webcam at 1711 15th september. If you read further down, the english translation of my message is at the bottom



Dear friend
We manage to communicate and to take pictures of every activity of the stargate we have a very interesting winter here in Skopelos.Thanks with the best wishesGeorge Michail

——-Original Message——-


Date: 12/9/2018 9:18:21 μμ


Subject: Αστρονομία στη Σκόπελο (Astronomy in Skopelos)

Γεια Σας  Γεώργιος , το όνομά μου είναι Ed, σας μίλησα στη Σκόπελο πριν από λίγες εβδομάδες στο φεστιβάλ. Είμαι ο αστρονόμος από την Αγγλία.

Μου άρεσε να μιλάω μαζί σας και με ενδιέφερε πολύ να μάθω ότι έχετε ένα παρατηρητήριο στο νησί. Θα ήθελα να έρθω και να το δω την επόμενη φορά που θα είμαι εκε

Είμαι μέλος της Ομάδας Αστρονομίας Rosliston που συναντάει κοντά στο Burton on Trent στην Αγγλία (

Αν κοιτάξετε την Αρχική σελίδα, εγώ είμαι στην πρώτη φωτογραφία (μπλε παλτό) και την 5η φωτογραφία (λευκό πουλόβερ). Μάλλον θα με αναγνωρίσεις από αυτό

Έχω επισυνάψει ορισμένες φωτογραφίες που πήρα. Ήταν τόσο ωραίο να βλέπετε κάποιον άλλον να κάνει δημόσια εκδηλώσεις προβολής. Κάνουμε αρκετά στο κλαμπ μας

Είπα σε άλλα μέλη για το γεγονός της Σκοπέλου και ήταν πολύ ζηλιάρης για το πόσο καθαρός ήταν ο ουρανός

Θα ήταν καλό να μοιράζεστε μαζί σας πληροφορίες και φωτογραφίες, αν θέλετε, και αν έρχεστε ποτέ στο Ηνωμένο Βασίλειο, θα ήσαστε πολύ ευπρόσδεκτοι να έρθετε στις συναντήσεις του συλλόγου μας

Θα σας δούμε το επόμενο έτος το 2019


My Greek is not very good so I have written it again in English just in case

Hi George, My name is Ed, I spoke to you in Skopelos a few weeks ago at the festival. I am the astronomer from England

It was great talking to you and I was very interested to know you have an observatory on the island. I woiuld like to come and see it next time I’m there

I’m a member of the Rosliston Astronomy Group that meets near Burton on Trent in the UK   (

If you look at the Home page, that’s me in the 1st  photo (blue coat) and the 5th photo (white jumper). You’ll probably recognise me from that

I have attached some photos that I took . It was so nice to see someone else doing public outreach events. We do quite a few in our club

I told the other members about the Skopelos event and they were very jealous of how clear the sky was

It would be good to share information and pictures with you if you’d like, and if you ever come to the UK, you’d be very welcome to come to our club meetings

Bye for now