… You could try this technique ( but hopefully you won’t need to anytime soon):
If the light on the laryngoscope fails, clean the contact between the blade and the handle, and check that the bulb is screwed in place securely. If this fails, use your spare laryngoscope, which you should have instantly available. Or, transilluminate his pharynx by shining an electric light through his neck as in Fig 13-12. If you don’t have a laryngoscope you can use a bent spoon – from King M, et al (1986). Primary Anaesthesia. Oxford Medical Publications.