Arunas Eimulis Posted November 24, 2017 Share Posted November 24, 2017 I have acquired some old 2,5K and 4K HMI's. Both are dedicated 2,5k and 4k ballasts. 4k ballast is twice as big as 2,5k. When testing them I noticed that 2,5K LTM HMI gives the same light output as 4k Sirio HMI. I don't have a light meter to do the accurate test, but to my eye and on the camera it seems to give the same light output on spot and flood setting, see pictures attached. What could be the reason? Why 4k is not brighter? Both lights has new Chinese bulbs now, but the output was the same with used Osram bulb on 4K. Can it be the bulb? Ballast? Or something else? Link to comment Share on other sites More sharing options...
Mark Dunn Posted November 24, 2017 Share Posted November 24, 2017 There's no way to judge without a meter. The eye compensates. Likewise we can't tell whether you exposure for each shot was identical. The spot setting is clearly brighter. Link to comment Share on other sites More sharing options...
Stefano Stroppa Posted November 24, 2017 Share Posted November 24, 2017 Do you have any fresnel lens attached at the front? Link to comment Share on other sites More sharing options...
Arunas Eimulis Posted November 24, 2017 Author Share Posted November 24, 2017 Yes, they both are fresnels and have fresnel lenses Link to comment Share on other sites More sharing options...
Michael Rodin Posted November 24, 2017 Share Posted November 24, 2017 (edited) Output also depends a lot on the reflector and (not as much) on lens diameter. And Sirios have smaller lenses than old-school fixtures like LTM Luxarc - but that doesn't make them 2x less in output, of course. Check if the reflectors are clean, make sure the ballass are set to correct mains voltages (big magnetic ballast have separate primary winding taps for 250, 230, 200V, etc). I won't trust my eyes in such a test, lights are something like 50 000 and 30 000 lux spotted, kind of hard to distinguish in a dim room. Edited November 24, 2017 by Michael Rodin Link to comment Share on other sites More sharing options...
Arunas Eimulis Posted November 29, 2017 Author Share Posted November 29, 2017 Thank you for help, I'll order light meter, time to start use it anyway :) Link to comment Share on other sites More sharing options...
Dennis Hingsberg Posted December 13, 2017 Share Posted December 13, 2017 Sekonic L-508 zoom master is a great meter you can get one used for very little. Features a spot meter as well as incident which can be handle if you want to measure reflectivity vs incident (light falling on meter). Link to comment Share on other sites More sharing options...
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