The stock DTR headlight takes a P45T bulb (similar fitting to H4) and has AC lighting (i.e the power for the lights comes straight from the magneto without involving the battery) so you can run a 100/80W halogen bulb without flattening the battery unlike a lot of bigger bikes which run DC. The DTR’s actual light lens/reflector is the same as all Yamaha superbikes of the 80s like the RD500LC and XJ900, but Yamaha cheaped out and fitted a 45/40W candle to the DTR which is why lots of people don’t find it bright enough. 100/80W bulb lights up the roads/trails like a rally car and retains an MOT-friendly beam pattern. Once a year or two ago I met up with a bunch of guys greenlaning on modern KTMs and decided to tag along with them as it was getting dark; they couldn’t believe how much brighter my headlight was. Get this one:

https://www.ebay.co.uk/itm/161339938963?hash=item25909c1893:g:1~UAAOSwewJTn~QT&amdata=enc%3AAQAIAAAAwF8Gw72CnU%2FbU0Zeu1tjSRJFvfcr8SwbZT4fRnA6WLf6yF0iSX4F43bpTTUSgtfBlW1qXJSqMRtuS3Z1Luu%2FAD2VbsWrYvQrEc7oksN8VfDpaJHi6ZYW7zMtJnc%2F1be5np%2B6CZfap%2Frggb9cb01JyCQriOkPtIXXi8yWcKEn3mLr0%2Bhj6%2FoeZKr0o8Jl3vVA6Hka4%2F2xaD1awxGTbT2XEJFqjhxzyuYbuNe8sKHYOq%2Fho75%2FaGbmg%2FihQpqKGR%2B4kA%3D%3D|tkp%3ABk9SR6iwz8zLYg