Eu acredito que você está procurando a coleção Contos de Dez Mundos (1962).
A primeira história é "Haja luz" (1957).
Um personagem criticou o modo como os raios da morte na ficção científica eram visíveis ao olho humano, dizendo que, se a luz visível fosse mortal, os humanos não poderiam viver.
Alguém viu os faróis de um carro atravessando uma sinuosa estrada montanhosa à noite e focalizou um holofote no telescópio do carro, cegando temporariamente o motorista que partiu de um penhasco até a morte.The conversation had come around to death rays again, and some carping critic was poking fun at the old science fiction magazines whose covers so often displayed multicoloured beams creating havoc in all directions. ‘Such an elementary scientific blunder,’ he snorted. ‘All the visible radiations are harmless—we wouldn’t be alive if they weren’t. So anybody should have known that the green rays and purple rays and scots-tartan rays were a lot of nonsense. You might even make a rule—if you could see a ray, it couldn’t hurt you.’
‘At last he saw the headlights of the car flickering on the horizon, and rather reluctantly broke off his observations. When the car had disappeared behind the hill, he was waiting with his hand on the switch. His timing was perfect; the instant the car came round the curve and the headlights shone on him he closed the arc.
‘Meeting another car at night can be unpleasant enough even when you are prepared for it and are driving on a straight road. But if you are rounding a hairpin bend, and know that there is no other car coming, yet suddenly find yourself staring directly into a beam fifty times as powerful as any headlight—well, the results are more than unpleasant.
‘They were exactly what Edgar had calculated. He switched off his beam almost at once, but the car’s own lights showed him all that he wanted to see. He watched them swing out over the valley and then curve down, ever more and more swiftly, until they disappeared below the crest of the hill.
E a segunda história é "Um leve caso de insolação" (1958).
Milhares de pessoas angularam objetos semelhantes a espelhos nos ângulos apropriados para concentrar a luz solar milhares de vezes em sua vítima que foi morta pelo calor intenso.
Um público de futebol descontente brindou ao árbitro, por esta revisão :
Some of the home audience became hysterical with anger and threatened to storm the field, but not the disciplined military personal among them. After the teams retreated to the sidelines, leaving the head r eferee isolated in the center of the field, there was a shrill bugle sound, and in unison the military personal each lifted his shinny program and angled it in the bright sunlight. All those programs formed a giant, curved mirror, with the focal point dire ctly on the referee. With a brilliant flash, the referee was transformed into a "smoldering heap" from which rose a column of smoke. In some countries, soccer is taken quite seriously.
Encontrado com a consulta do Google "arthur c clarke" "visible light" que retornou a página da Wikipédia de "Let there be light" . Em seguida, passei as histórias listadas nas principais coleções em que aparecia até encontrar "Um pequeno caso de insolação".