In the late ’70s, a new type of lighting was introduced. The first range were called CSI lights and they were using some kind of a pulse, I think, within the bulb which generated a daylight colour. The problem with them was that the... from one lamp to the next the colour varied, so CSI lamps never really caught on but very soon after that there was a new development of HMI lamps which provided daylight colour from an alternating current source whereas with brutes you see, you needed direct current. You could plug in these lamps in... into your household supply. And the first lamps that came out were 2.5kW, so you could plug them in to the household supply and you got this brilliant lamp of daylight colour- 5600K- and it didn't produce much heat; so that was quite an advantage when you were shooting in... inside, because previously, if we were shooting with... match... trying to match daylight, you'd have to take the tungsten lamp and put a full blue filter on and care... carefully check the colour temperature to see if it matched the daylight. Sometimes you'd have to put more than a full blue, so you'd use an awful lot of light level by adding this blue. So this was a whole new development and they started off just with a 2.5kW and then various other sizes followed. And it was a marvellous new development.

I was to actually make a mistake when they were first brought out because nobody realised quite how important the flicker was. You... because this is a pulsed lamp which is going on and off every 50 seconds, every 1/50th of a second, sorry, every 1/50^th of a second there's a pulse, it means that you've got to synchronise the camera shutter to that pulse, and if you were coming off a 50 cycle supply and you were shooting at 24 frames on the camera, you had to have a shutter opening of 172.8 I think, and if you were shooting at 25 frames on the camera coming off a 50 cycle supply, you had to shoot with 180 shutter. Well, when the first... lamps first came out, we didn't realise that there was what we call a very narrow window where you wouldn't get any flicker and these lamps came out and I used them on a commercial and when we saw the rushes there was a slight flicker which couldn't be eliminated, and I was in a certain amount of trouble with the producer. And John and Benny Lee then went back to the drawing board and they produced a new... new generation of HMI lamps which are called Square Wave, which meant that you wouldn't get the flicker, even if you didn't have the correct shut... shutter aperture, so that you could then change the shutter aperture if you wanted to without... without getting the problems of flicker. So, these were things that we learnt along the way and now they're accepted on... on every shoot where you're involving daylight. What you do have to be careful with them, though, is when you first switch them on, they're not the right colour temperature. They have a... a cyan bias and it sometimes takes a minute or two while the lamp warms up until it's reached the proper temp... colour temperature and if you shoot before they're warmed up, you get a cyan bias on the skin tone, which... which can be really unpleasant. So I... I always check with a colour temperature meter all... all the HMI lamps just to make sure they balance one another.