I just thought I'd show you four Tilleys running after I'd been doing some light meter tests. The lamp on the extreme right is an X246B-500 series, and it measures 71% brighter than the standard X246B on the far left. The two in the centre are Guardian X246s. Phil
Hello Phil, it does look brighter, but as you know, there are so many aspects which affect light output. Not Gaurdian, they are Guardsman lanterns and you could try fitting the 500 series kit to one of them, as those tanks will handle the pressure better. If they any of those two tanks are undated, then that's the one to use, because it will be a better built tank, Jeff.
Guardian? What was I thinking? Of course it's Guardsman! I knew that. Mind you, it was late last night when I posted the message... Good idea about swapping the 500 series kit over, and I might try that one day All the best, Phil
Hi Phil great display and light output test,i can see the 500 series brighter,but i am surprised it is 71% brighter than the rest
Thanks for that. For what it's worth, here are the actual footcandle readings from the lightmeter during my tests. Ignore the actual light levels, it's the difference between lamps that's relevant: Tilley X246B...........35 Guardsman 1..........45 Guardsman 2..........55 Tilley X246B/500.....60 The last reading is 71% higher than the first. Phil
I would expect a meter to read high because of reflected light and those readings seem to be very low. I understand the idea of relative measurement and it is revealing for sure. What distance did you use between meter and mantle? ::Neil::
Hi Neil, Yes, I agree, the meter is reading very low, and I suspect it may be faulty. I placed the footcandle meter exactly one foot (300mm) from the mantle, expecting the meter to consequently read directly in candlepower. The meter has two ranges, a X1 range dual-scaled at 0-50 footcandles and 0-500 lux, and a X5 range which reduces the sensitivity to 0-250 FC (0-2,500 lux). I expected to get readings in the 150-250 CP range. The meter itself is a simple device consisting of a selenium photocell, a variable resistance and a moving-coil milliammeter. Unfortunately I have no instructions for calibrating the meter. The selenium cell is probably duff. I've decided to compare it against several similar meters in a collection owned by an acquaintance locally. Phil
Well maybe the readings were near enough right then. I have had enough experience to know that you can easily get a bunch of Tilleys all shoving out under 100cp. As a rough guide see if you can find on old tungsten electric lamp bulb. I know roughly what they do and you might find the meter is not so bad. Because tungsten bulbs have a coiled strip inside they give a varied reading depending on the presentation of the strip so I recorded high and low for each. These readings will be a tad high. Perhaps by about 10% because they were taken before I baffled the light meter tube. 25w 23-30cp 40w 47-60cp 60w 77-99cp 100w 114-175cp 150w 221-308cp. I have not recorded what modern electric light bulbs do but maybe when I have the time I will have a go. ::Neil::
Hi Neil, Thank you very much for those very helpful comparisons between tungsten light bulbs and candlepower. I have just tried a 100 watt clear light bulb and got a reading of 95 CP, a lot lower than your reported range of 114-175 CP, which would seem to confirm that my light meter is reading low after all. I do have a selection of tungsten bulbs of other wattages, so it will be a relatively easy matter to see whether my light meter is anywhere near the correct calibration. In the interim, I have won another Avo Model 3 light meter for 99p. Whether this will be any more accurate remains to be seen! Phil
You might find some variation because I suspect Tungsten bulbs deteriorate a little with use. The bulbs I used back then were brand new and older bulbs may well read slightly lower.Probably not by much though and it does give you some idea. What was interesting was that a good working pressure lamp does not illuminate a room anywhere near as well as a ceiling mounted electric bulb. Pressure lamps tend to throw shadows because of the tanks but an electric bulb gains much from reflected light via a white painted ceiling. ::Neil::
