This page contains a Flash digital edition of a book.
TECHNOLOGY / THE ARC SHOW 183


Joe Bokelman gave a presentation to the IALD Enlighten Europe conference 2012 on the use of spectral equalisation to avoid potentially disastrous ‘metameric failure’. Here he reveals the principles behind this fresh approach to making colours ‘pop’.


BEYOND RGB: SPECTRAL EQUALISATION


Figure1: Left The hat is lit using cyan light. Right By adding an additional colour, in this case green, we can make both blue and green stand out – we can make it pop.


Lighting is an art – but it involves science. Everything we see is an interaction between the surfaces being looked at, the light available at the time, our eyes, and our brains. These factors make up our view of the world around us. What colour works, and what doesn’t, and why? When we use coloured or even white lights in our work as lighting designers, there are things that we think about, consciously or not. We perceive light based on information taken in by the eyes, and then interpreted by the brain – which is why you can’t neces- sarily trust a meter or gauge to tell the truth. Metamerism is ‘the matching of appar- ent colours with different spectral power distributions. Colours that match this way are called metamers’. Take the example of a car in a body shop that is being prepared for respray. A paint mixer will (hopefully)


look at the colour of the car, and mix up a paint that’s identical to it, rather than relying on the colour codes of the paint. But will they take the car outside to look under natural light, or just use the artifi- cial lighting of the workshop? If they just use artificial light, then they will be very likely to get it wrong. This is because only natural light is made up of all the colours of the rainbow. Trying to match up apparent colours under lights with different spectral power distributions is bound to end in fail- ure: metameric failure. Now, imagine the colours of the rainbow, with blues and violets at one end and reds at the other. This shows us the range of human vision; sunlight is simply a mix of all of these. A tungsten lamp is pretty good at replicating this light, which is why the lighting world is so keen on it. We then put filters in front to create coloured light,


which have pigments added to block certain colours, while allowing others to pass through. This is called subtractive colour mixing – and unfortunately, because it ab- sorbs so much light, it comes out very dim. For example, a deep blue gel might only allow 3% of visible light through; it stops everything else. That’s why you need such a powerful lamp to get much useful light out. But subtractive colour mixing is old technol- ogy. We now have something quite differ- ent: additive colour mixing, created by mixing lamps which are genuinely coloured at the source. LEDs. LEDs come in very narrow bands of colour – rather than the much wider bands from tungsten or natural light. This means that a blue LED only outputs blue light, rather than a wide range of colours which need to be blocked. LEDs just so happen to be very efficient in the areas where incandescent


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52  |  Page 53  |  Page 54  |  Page 55  |  Page 56  |  Page 57  |  Page 58  |  Page 59  |  Page 60  |  Page 61  |  Page 62  |  Page 63  |  Page 64  |  Page 65  |  Page 66  |  Page 67  |  Page 68  |  Page 69  |  Page 70  |  Page 71  |  Page 72  |  Page 73  |  Page 74  |  Page 75  |  Page 76  |  Page 77  |  Page 78  |  Page 79  |  Page 80  |  Page 81  |  Page 82  |  Page 83  |  Page 84  |  Page 85  |  Page 86  |  Page 87  |  Page 88  |  Page 89  |  Page 90  |  Page 91  |  Page 92  |  Page 93  |  Page 94  |  Page 95  |  Page 96  |  Page 97  |  Page 98  |  Page 99  |  Page 100  |  Page 101  |  Page 102  |  Page 103  |  Page 104  |  Page 105  |  Page 106  |  Page 107  |  Page 108  |  Page 109  |  Page 110  |  Page 111  |  Page 112  |  Page 113  |  Page 114  |  Page 115  |  Page 116  |  Page 117  |  Page 118  |  Page 119  |  Page 120  |  Page 121  |  Page 122  |  Page 123  |  Page 124  |  Page 125  |  Page 126  |  Page 127  |  Page 128  |  Page 129  |  Page 130  |  Page 131  |  Page 132  |  Page 133  |  Page 134  |  Page 135  |  Page 136  |  Page 137  |  Page 138  |  Page 139  |  Page 140  |  Page 141  |  Page 142  |  Page 143  |  Page 144  |  Page 145  |  Page 146  |  Page 147  |  Page 148  |  Page 149  |  Page 150  |  Page 151  |  Page 152  |  Page 153  |  Page 154  |  Page 155  |  Page 156  |  Page 157  |  Page 158  |  Page 159  |  Page 160  |  Page 161  |  Page 162  |  Page 163  |  Page 164  |  Page 165  |  Page 166  |  Page 167  |  Page 168  |  Page 169  |  Page 170  |  Page 171  |  Page 172  |  Page 173  |  Page 174  |  Page 175  |  Page 176  |  Page 177  |  Page 178  |  Page 179  |  Page 180  |  Page 181  |  Page 182  |  Page 183  |  Page 184  |  Page 185  |  Page 186  |  Page 187  |  Page 188  |  Page 189  |  Page 190  |  Page 191  |  Page 192  |  Page 193  |  Page 194  |  Page 195  |  Page 196  |  Page 197  |  Page 198  |  Page 199  |  Page 200  |  Page 201  |  Page 202  |  Page 203  |  Page 204  |  Page 205  |  Page 206  |  Page 207  |  Page 208  |  Page 209  |  Page 210  |  Page 211  |  Page 212  |  Page 213  |  Page 214  |  Page 215  |  Page 216  |  Page 217  |  Page 218  |  Page 219  |  Page 220  |  Page 221  |  Page 222  |  Page 223  |  Page 224  |  Page 225  |  Page 226  |  Page 227  |  Page 228