and on the local scene, Paul Richards from Nutshell
/ ŶŽǁ ĂĐƟǀ ĞůLJ Ăǀ ŽŝĚ > ůŝŐŚƟŶŐ͕ especially cheap stuff. We nearly lost a shoot in Hamilton for Rock Quest due to ƚŚĞ s ĞŶƵĞ ƉƌŽǀ ŝĚŝŶŐ ƚŚĞ ůŝŐŚƟŶŐ ĨŽƌ ƚŚĞ gig, which … like you say, did not show as Ă ƉƌŽďůĞŵ Ăƚ ƚŚĞ ƟŵĞ͘ /ƚ ǁ ĂƐ Ă ŵĂũŽƌ ŝƐƐƵĞ ĨŽƌ ƚŚĞ ƉƌŽĚƵĐƟŽŶ ĂŶĚ ŵƵĐŚ ŚĞĂĚ ƐĐƌĂƚĐŚŝŶŐ ĂŌĞƌǁ ĂƌĚ͘ ZĞƐĞĂƌĐŚ ŚĂƐ ŶŽǁ revealed that CCD and CMOS sensors react differently to LED. ^ŚŽŽƟŶŐ Ă ƚĞƐƚ ŝƐ ǀ ŝƚĂů ĂŶĚ ĞŵƉůŽLJŝŶŐ , LJƉĞƌ-gamma or a ƐŚƵƩ Ğƌ Žƌ ďŽƚŚ ƐĞĞŵƐ ƚŽ ďĞ ƚŚĞ ďĞƐƚ ƐŽůƵƟŽŶ͘ and from Clive Cannon, Technical Product Specialist, Sony ANZ
Firstly this is a completely different issue to the one that I am aware of with LED lights – especially blue, and that relates to CCD not CMOS. The issue described appears to be much the same as the issue one would expect to get with fluorescent lights, but more severe. CMOS sensors acquire differently to CCD ƐĞŶƐŽƌƐ͖ ŝŶ ƐŝŵƉůŝƐƟĐ ƚĞƌŵƐ ƐĞŶƐŽƌƐ ƚĂŬĞ Ă ƐŶĂƉ ŽĨ ƚŚĞ ĞŶƟƌĞ Į ĞůĚͬ ĨƌĂŵĞ ǁ ŚĞƌĞĂƐ D K ^ ƐĞŶƐŽƌƐ ƐĐĂŶ ĨƌŽŵ ƚŽƉ ƚŽ ďŽƩ Žŵ ŽĨ ƚŚĞ ĨƌĂŵĞ͘ dŚĞƌĞĨŽƌĞ ǁ ŝƚŚ D K ^͕ ŝĨ ƚŚĞ ŝŵĂŐĞͬ ůŝŐŚƟŶŐ ĐŚĂŶŐĞƐ ĚƵƌŝŶŐ ƚŚĞ ƉĞƌŝŽĚ ŽĨ ƟŵĞ ƚŚĂƚ ƚŚĞ ƐĞŶƐŽƌ ŝƐ ƐĐĂŶŶŝŶŐ͕ ƚŚĞŶ ŝƚ ǁ ŝůů ďĞ ƌĞƉůŝĐĂƚĞĚ on the recorded picture. In the case of an LED light switching on/off/on /off fast ( i.e PWM ), then of course this is going to be captured by the sensor and seen as horizontal banding. Fluorescent lamps do a similar thing but with much less severe results due to ƚŚĞ ŚLJƐƚĞƌĞƐŝƐ ŽĨ ƚŚĞ ƉŚŽƐƉŚŽƌ Ğŵŝƫ ŶŐ ƚŚĞ ůŝŐŚƚ͕ ŚŽǁ Ğǀ Ğƌ ƚŚĞ ƉŝĐƚƵƌĞ ŵĂLJ ƐƟůů ďĞ ƐĞĞŶ ƚŽ ŚĂǀ Ğ ŵŝůĚ ŚŽƌŝnjŽŶƚĂů ďĂƌƐ ƌƵŶŶŝŶŐ ƚŚƌŽƵŐŚ ĚĞƉĞŶĚĞŶƚ ƵƉŽŶ ƐŚƵƩ Ğƌ ƐƉĞĞĚ ĞƚĐ͘ ^ŚƵƩ Ğƌ ƐŚŽƵůĚ Ăůǁ ĂLJƐ ďĞ K && ǁ ŚĞŶ ƐŚŽŽƟŶŐ ƵŶĚĞƌ fluorescent lights. Many professional camcorders with CMOS sensors have a flicker reduce feature for use with fluorescents.
Professional fluoro units ( Kinoflo, Lowel, etc ) all use high frequency ballasts which drive the lamps at a rate well ĂďŽǀ Ğ ŐĞŶĞƌĂů ĐĂŵĞƌĂ ƐĐĂŶ ĂŶĚ ƐŚƵƩ Ğƌ ƌĂƚĞƐ͘ dŚĞ ďĂŶĚŝŶŐ and flicker issues that you see are the same as have always occurred with any light source driven by an AC waveform. ĂƩ ĞƌLJ Žƌ ŵĂŝŶƐ ƐŚŽƵůĚŶΖƚ ŵĂƩ Ğƌ͘ /Ĩ ƚŚĞLJ ĂƌĞ Ěƌŝǀ ĞŶ Žī mains they will generally use a DC power supply to run the unit. As all the notes state, the strobing issue is about the frequency of the PWM dimming that most cheap units use to control intensity. t ŝƚŚ ƌĞŐĂƌĚ ƚŽ ƚŚĞ > ƵŶŝƚƐ͕ Ăůů ŽĨ ƚŚĞ ŝŶĨŽƌŵĂƟŽŶ LJŽƵ have provided is accurate. Paul's problem is one that is ŐŽŝŶŐ ƚŽ ďƵŝůĚ ƵƉ ĨŽƌ Ğǀ ĞƌLJŽŶĞ ƐŚŽŽƟŶŐ ŝŶ ůŝƚ ĞŶǀ ŝƌŽŶŵĞŶƚƐ which are not under their direct control. There is a vast drive to use LED colour changing fixtures to light everything and most of these are the cheapest units available. There are a large number of very good and pricey LED colour changers on the market, but not a lot of them end up in places we are going to shoot. If you need to shoot in a suspect environment, as Paul says, shoot a test. It may result in you having to tell your client ƚŚĂƚ ƚŚĞ ůŝŐŚƟŶŐ ŝƐ ŶŽƚ ƵƉ ƚŽ ƐƉĞĐ ĂŶĚ LJŽƵ ĐĂŶΖƚ ƐŚŽŽƚ ƚŚĞŝƌ Ğǀ ĞŶƚ͘ WĞƌŚĂƉƐ ƐŚŽŽƚĞƌƐ ĂŶĚ ƉƌŽĚƵĐƟŽŶ ĐŽŵƉĂŶŝĞƐ ŶĞĞĚ ƚŽ ƉƵƚ Ă ĐĂǀ ĞĂƚ ĂďŽƵƚ ƐŚŽŽƟŶŐ ŝŶ ƉƌĞ-ůŝƚ ƐĞƫ ŶŐƐ ŽŶ ƋƵŽƚĞƐ and proposals. dŚĞ ŬĞLJ ƉŽŝŶƚ / ĨĞĞů ŝƐ ƚŽ ƵƐĞ Ă ƌĞƉƵƚĂďůĞ ůŝŐŚƟŶŐ ƐƵƉƉůŝĞƌ͖ Trade Me is not one!! Any supplier worth their salt will be aware of the PWM strobing issues. Buy fixtures with brands that you recognise on them.
and Chris McKenzie, Professional Lighting Services, NZ
Firstly I agree with Clive. The key point with all of these fixtures is the level of ΗƉƌŽĨĞƐƐŝŽŶĂůΗ ƋƵĂůŝƚLJ ǁ Ğ ĂƌĞ ĞdžƉĞĐƟŶŐ from "prosumer" level product in the marketplace. New Zealand users are all ǀ ĞƌLJ ƉƌŝĐĞ Ěƌŝǀ ĞŶ ĂŶĚ ĂƌĞ ŵŽƟǀ ĂƚĞĚ ƚŽ shop around for the "best" deal. ^ŽŵĞƟŵĞƐ ƚŚĂƚ ďĞƐƚ ĚĞĂů ŝƐ ŶŽƚ͘ t ŝƚŚ ƌĞŐĂƌĚ ƚŽ ƚŚĞ ŇƵŽƌŽ ŝƐƐƵĞƐ ŵĞŶƟŽŶĞĚ ďLJ ůŝǀ Ğ͕ ƚŚĞƐĞ ǁ ŝůů ŐĞŶĞƌĂůůLJ ƐŚŽǁ ƵƉ ǁ ŝƚŚ ŵĂŐŶĞƟĐ ďĂůůĂƐƚ Ěƌŝǀ ĞŶ ŇƵŽƌŽƐ ŝŶ ŝŶƐƚĂůůĂƟŽŶƐ͕ Žƌ ŝŶ ĐŚĞĂƉŽ Į ƫ ŶŐƐ͘
So, what should you do? If you already have an LED or Fluoro panel and you are using CMOS or CCD cameras, you need to do tests at different dimmed levels. If you are planning to buy a new light or two, be well aware of the issues. Ed. NZVN
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