首楞嚴義疏注經 5.409

5.409

定光佛，即然燈佛也。由觀四大虛妄有生，無物可得，同於虛空，故得身相猶如虛空，周遍無礙也。

The Buddha of Fixed Light is precisely Dīpaṃkara Buddha ('Burning Lamp'). Through contemplating that the four great elements have delusive arising, that no thing is to be found, and that they are identical to empty space, he therefore attained a bodily characteristic like empty space, all-pervading and unobstructed.