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My enlarger bulb must be near the end of its life. So in readiness, I recently bought on eBay what I thought was a NOS 150W screw-mount Philips Photocrescenta enlarger bulb. What I received was a Chinese-made 'Photolux' copy. I found that quite annoying, as Photocrescenta (and its Philips code) were the title of the advert, and the label on the image. More fool me, I was pleasantly surprised to find one, and should have looked carefully in that image at the lettering on the bulb.
I gave the supplier a poor review for misleading advertising, and because I had no idea whether what I received was a reasonable substitute. Afterwards, it occurred to me that in fairness I could do a side-by-side comparison of the output wavelengths using the Lightspectrum Pro app on my phone. I measured the light as projected off the enlarging easel, without filters, and with each of the Ilford MG under-lens filters in place (whole grades only). The results are attached. The larger numbers on the right of each screenshot are (top to bottom) deg Kelvin, tint, Lux, and G-index (the latter two are not relevant here, I think). Perhaps someone wiser than me could suggest whether or not the small differences observed mean anything / are likely to be be significant in practice? I have not yet made a print with the bulb, nor tested coverage over the baseboard.
All of these measurements were made with room lights and safelights off, at my usual operating aperture of f/8. One odd thing I had noticed at the outset was that when there was no filter under the lens, stopping down the lens caused the spectrum both to broaden slightly and to shift slightly along the x-axis. This did not happen with a filter in place. I have a suspicion it may have more to do with the app than with any optical phenomenon, but please tell me if you can think of an optical explanation.
Before anyone else leaps in, I was also surprised that the filters did not make a consistent series, but I checked carefully and (for example) the one labelled G3 definitely was taken using G3. I also don't understand how the filters can produce wavelengths that apparently were absent in the unfiltered light. I clearly don't understand enough about the physics of light and would appreciate insights from those who do.
I must add that the Photolux bulb is distinctly askew in its screw mount, and in general it gives an impression of sloppy manufacturing quality compared with the Philips. But if it is good enough, so what?
I'd also be interested to know the experiences of anyone using LED bulbs in a Philips enlarger.
I gave the supplier a poor review for misleading advertising, and because I had no idea whether what I received was a reasonable substitute. Afterwards, it occurred to me that in fairness I could do a side-by-side comparison of the output wavelengths using the Lightspectrum Pro app on my phone. I measured the light as projected off the enlarging easel, without filters, and with each of the Ilford MG under-lens filters in place (whole grades only). The results are attached. The larger numbers on the right of each screenshot are (top to bottom) deg Kelvin, tint, Lux, and G-index (the latter two are not relevant here, I think). Perhaps someone wiser than me could suggest whether or not the small differences observed mean anything / are likely to be be significant in practice? I have not yet made a print with the bulb, nor tested coverage over the baseboard.
All of these measurements were made with room lights and safelights off, at my usual operating aperture of f/8. One odd thing I had noticed at the outset was that when there was no filter under the lens, stopping down the lens caused the spectrum both to broaden slightly and to shift slightly along the x-axis. This did not happen with a filter in place. I have a suspicion it may have more to do with the app than with any optical phenomenon, but please tell me if you can think of an optical explanation.
Before anyone else leaps in, I was also surprised that the filters did not make a consistent series, but I checked carefully and (for example) the one labelled G3 definitely was taken using G3. I also don't understand how the filters can produce wavelengths that apparently were absent in the unfiltered light. I clearly don't understand enough about the physics of light and would appreciate insights from those who do.
I must add that the Photolux bulb is distinctly askew in its screw mount, and in general it gives an impression of sloppy manufacturing quality compared with the Philips. But if it is good enough, so what?
I'd also be interested to know the experiences of anyone using LED bulbs in a Philips enlarger.
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